drinking water while eating research

Fact check: Drinking water while eating does not lead to digestive issues

The claim: Drinking water while eating can prevent your body from properly absorbing nutrients

There are many well-known health benefits to drinking water such as aiding digestion and metabolism. But a recent Instagram meme urges users to refrain from drinking water while eating, claiming that it can lead to serious health issues. 

"DID YOU KNOW?" starts an Aug. 5 Instagram post , which has over 2,500 likes.

The post goes on to claim that drinking water while eating prevents the body from absorbing nutrients properly, causes bloating and leaking of undigested food into your system.

The text meme further claims it could cause acid reflux and heartburn, a surge in insulin levels, and increase the chances of storing fat in your body.

USA TODAY reached out to the user for comment. 

Fact check : Fruit does not hydrate the body twice as much as a glass of water

Studies, experts: No evidence of negative impact from drinking water with a meal

According to studies and experts, there is no concern that drinking water while eating will disturb digestion and cause health problems.

Michael Picco, an assistant professor of medicine at College of Medicine, Mayo Clinic, wrote in response to a frequently asked question that there is "no concern that water will dilute the digestive juices or interfere with digestion."

"Water is essential for good health," Picco, who is also a consultant in gastroenterology at Mayo Clinic in Florida, wrote . "Water and other liquids help break down food so that your body can absorb the nutrients. Water also softens stool, which helps prevent constipation."

The study " Gastric emptying of a physiologic mixed solid-liquid meal ," published in 1982 in Clinical Nuclear Medicine, found that ingesting liquids simultaneously did not affect the rate at which solids cleared from the stomach.

Other experts have also emphasized there is no evidence that water consumption during a meal has negative impacts.

Debbie Fetter , an assistant professor of teaching nutrition at the University of California, Davis, told USA TODAY that there is no research showing that drinking water while eating is harmful. She said it can actually prevent bloating and aid in digestion. 

"It helps slow the eating process and create a smoother digestion process," Fetter said. "Having sips of fluid while eating can also help people with overeating."

Maria Moore, an Atlanta-based dietician, told Southern Living , "We're not aware of any findings that a reasonable amount of water would negatively impact digestion. The stomach maintains a very acidic environment and is quite adaptable. In healthy people, the stomach secretes enough fluid and acid to accommodate the meal and get the digestion process started."

Tamara Duker Freuman, a registered dietitian and author of "The Bloated Belly Whisperer," told the Washington Post that the theory that you shouldn't drink water before or while eating is "totally false."

Nestlé also took to its site to debunk the myth that drinking water with a meal can lead to bloating. 

"A glass of water, when sipped slowly during a meal can actually aid digestion rather than cause any bloating!" the company's site states in a "Myth Busters" section , adding that juices and carbonated beverages can delay the digestion process.

Fact check: Instant noodles don't contain wax coating or cause cancer

Drinking water while eating can provide benefits 

While the post claims that drinking water while eating increases the chances of storing fat in your body, research shows it can actually help with weight loss and provide other benefits, contrary to the viral claims.

Ilana Muhlstein, a weight loss expert who is part of the executive leadership team for the American Heart Association,  told The Thirty that drinking water satisfies hunger hormones and leads to a "sense of calmness and fullness."

Muhlstein also noted that all foods already contain water. 

"If you're eating a big salad, you are literally chewing water," Mulhstein said, who also leads the Bruin Health Improvement Program at UCLA. "Why wouldn't you be able to have a sip of water with that?"

Yashoda Hospitals, a chain of hospitals in Hyderabad, India, writes on its site , "Water is any day the healthiest choice and will not interrupt your digestion even if taken in large quantities. Even after one has had a heavy meal, a decent amount of water cannot do any harm."

The site notes the many benefits of consuming water even after a meal include nutrient absorption, reducing calorie intake, preventing constipation, softening stool and preventing bloating.

Our ruling: False

There is no research or evidence to support the claim that drinking water while eating a meal can interfere with digestion, cause bloating, lead to acid reflux or have other negative health effects. Many studies and experts say that drinking water while eating can actually aid the digestion process. We rate this claim FALSE because it is not supported by our research. 

Our fact-check sources:

• Mayo Clinic, April 18,  Does drinking water during or after a meal disturb digestion?
• National Library of Medicine, " Gastric emptying of a physiologic mixed solid-liquid meal "
• Southern Living, How Bad is it to Drink Water While Eating? We Asked the Experts
• Washington Post, April 22, 2019, There’s a persistent myth that you shouldn’t drink water while eating. You can disregard it.
• Nestlé, Myth Busters: Drinking water with meals causes bloating
• The Thirty, Aug. 2,  This Is the Secret to Better Digestion, According to Nutritionists
• Yashoda Hospitals, Feb. 20, Does drinking water after meals disturb digestion?
• Asst. Prof. Debbie Fetter, UC Davis , USA TODAY interview
• USA TODAY, Jan. 23,  Why you should drink water first thing every day

Thank you for supporting our journalism. You can  subscribe to our print edition, ad-free app or electronic newspaper replica here .

Our fact check work is supported in part by a grant from Facebook.

Appointments at Mayo Clinic

• Nutrition and healthy eating

Does drinking water during or after a meal affect or disturb digestion?

There's no concern that water thins down or weakens down (dilute) the digestive juices or interfere with digestion. In fact, drinking water during or after a meal helps how your body breaks down and processes food (digestion).

Water is vital for good health. Water and other drinks help break down food so that your body can take in (absorb) the nutrients. Water also makes stool softer, which helps prevent constipation. Choose water when possible instead of drinks full of sugar.

Looking for other ways to promote good digestion? Live a healthy life. Eat plenty of fruits, vegetables and whole grains. Also include low-fat or fat-free milk, yogurt and other dairy products and lean meats. Keep a healthy weight. Get active most days of the week.

Michael F. Picco, M.D.

There is a problem with information submitted for this request. Review/update the information highlighted below and resubmit the form.

From Mayo Clinic to your inbox

Sign up for free and stay up to date on research advancements, health tips, current health topics, and expertise on managing health. Click here for an email preview.

Error Email field is required

Error Include a valid email address

To provide you with the most relevant and helpful information, and understand which information is beneficial, we may combine your email and website usage information with other information we have about you. If you are a Mayo Clinic patient, this could include protected health information. If we combine this information with your protected health information, we will treat all of that information as protected health information and will only use or disclose that information as set forth in our notice of privacy practices. You may opt-out of email communications at any time by clicking on the unsubscribe link in the e-mail.

Thank you for subscribing!

You'll soon start receiving the latest Mayo Clinic health information you requested in your inbox.

Sorry something went wrong with your subscription

Please, try again in a couple of minutes

• Underweight: Add pounds healthfully
• What is BPA?
• Perrier ET. Shifting focus: From hydration for performance to hydration for health. Annals of Nutrition & Metabolism. 2017; doi:10.1159/000462996.
• Make better beverage choices. U.S. Department of Agriculture. https://www.myplate.gov/tip-sheet/make-better-beverage-choices. Accessed April 6, 2022.
• Water and healthier drinks. Centers for Disease Control and Prevention. https://www.cdc.gov/healthyweight/healthy_eating/water-and-healthier-drinks.html. Accessed April 6, 2022.
• 2020-2025 Dietary Guidelines for Americans. U.S. Department of Health and Human Services and U.S. Department of Agriculture. https://www.dietaryguidelines.gov. Accessed April 6, 2022.
• Picco MF (expert opinion). Mayo Clinic. April 25, 2022
• Duyff RL. Academy of Nutrition and Dietetics Complete Food and Nutrition Guide. 5th ed. Houghton Mifflin Harcourt; 2017.
• Khanna S, ed. Recipe for healthy digestion. In: Mayo Clinic on Digestive Health. 4th ed. Mayo Clinic Press; 2020.

Products and Services

• A Book: Cook Smart, Eat Well
• The Mayo Clinic Diet Online
• A Book: The Mayo Clinic Diet Bundle
• A Book: Mayo Clinic on Digestive Health
• Butter vs. margarine
• Caffeine content
• Clear liquid diet
• DASH diet: Recommended servings
• Sample DASH menus
• Diverticulitis attack triggers
• Diverticulitis diet
• Eggs and cholesterol
• Enlarged prostate: Does diet play a role?
• Fasting diet: Can it improve my heart health?
• Gluten sensitivity and psoriasis: What's the connection?
• Gluten-free diet
• Gout diet: What's allowed, what's not
• Intermittent fasting
• Low-fiber diet
• Low-glycemic index diet
• Mediterranean diet
• Picnic Problems: High Sodium
• Nutrition and pain
• Vegetarian diet

Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission.

• Opportunities

Mayo Clinic Press

Check out these best-sellers and special offers on books and newsletters from Mayo Clinic Press .

• Mayo Clinic on Incontinence - Mayo Clinic Press Mayo Clinic on Incontinence
• The Essential Diabetes Book - Mayo Clinic Press The Essential Diabetes Book
• Mayo Clinic on Hearing and Balance - Mayo Clinic Press Mayo Clinic on Hearing and Balance
• FREE Mayo Clinic Diet Assessment - Mayo Clinic Press FREE Mayo Clinic Diet Assessment
• Mayo Clinic Health Letter - FREE book - Mayo Clinic Press Mayo Clinic Health Letter - FREE book
• Healthy Lifestyle
• Expert Answers
• Water after meals Does it disturb digestion

Your gift holds great power – donate today!

Make your tax-deductible gift and be a part of the cutting-edge research and care that's changing medicine.

• Skip to main content
• Keyboard shortcuts for audio player

• Dear Life Kit
• Life Skills

• LISTEN & FOLLOW
• Apple Podcasts
• Google Podcasts
• Amazon Music

Your support helps make our show possible and unlocks access to our sponsor-free feed.

Busting 5 common myths about water and hydration

Aaron Scott

Summer Thomad

Subscribe to Life Kit's weekly newsletter and get expert advice on lifestyle topics like money, relationships, health and more. Click here to subscribe now .

For more ideas on how to improve your life, explore Life Kit's New Year's Resolution Planner .

Drink eight glasses of water a day. Coffee will make you dehydrated. Drinking extra water can help you lose weight.

You've probably heard these claims about water and hydration before. But are they true?

To set the record straight, Life Kit talks to Tamara Hew-Butler , associate professor of exercise and sports science at Wayne State University; Mindy Millard-Stafford , director of the Exercise Physiology Laboratory at Georgia Tech; and Yuki Oka , a professor of biology at Caltech who specializes in thirst.

They explain the science of hydration and bust 5 common myths about water.

Myth #1: You need to drink at least eight glasses of water a day.

Is the advice of drinking eight, 8-ounce glasses of water a day to stay hydrated true? Researchers in 2002 tried to pin down studies that might support the claim by looking through multiple scientific databases — but were unable to find rigorous evidence behind it.

What we do know, says Hew-Butler, is that water is essential for our bodies. It makes up a majority of our cells and blood, flushes out waste through our urine and helps cool our bodies through sweat. Too little water, and our cells shrivel up from dehydration. Too much water, and our cells swell up from hyponatremia.

So how much water should we be drinking on a daily basis? It depends, says Hew-Butler, on your body size, your activity level, the temperature and how much you're sweating.

Because of these factors, there's no hard and fast rule for how much water you should consume. "The best advice is to listen to your body," she says. "If you get thirsty, drink water. If you're not thirsty, you don't need to drink water."

"This will protect you against the dangers of both drinking too much and drinking too little," she adds. "And this recommendation applies to [people of] all shapes and sizes in all temperature conditions."

Hew-Butler says hydration is also about the balance of water to salt. Sodium is necessary for our nerves and muscles to function. And it's what our body uses to regulate the amount of fluid it needs to stay hydrated.

Thirst plays a central role in fine-tuning that balance, she explains. "There are sensors located in your brain and they are constantly tasting your blood to see if [there's] just the right [amount of] salt. If it's too salty, then [those sensors are] like, 'Oh my God, I need more water.' When that happens, it makes you thirsty."

Then, if you drink too much water and the sensors in your brain detect that your blood is too watery, they signal a hormone that tells your kidneys to pee out the extra water, she says.

In short: you don't need an app to tell you how much water to drink or guzzle a gallon of water a day – just trust your body to let you know when to drink water, says Hew-Butler.

There are, however, a few exceptions. Some research suggests that older people may have a reduced sensitivity to thirst and a decreased amount of water in their bodies — and are therefore at higher risk of dehydration . So they may need to be more intentional about their water intake. And other research has demonstrated that drinking more water can help with certain medical conditions, including kidney disease , kidney stones and urinary tract infections .

Myth #2: Caffeine makes you dehydrated.

Another persistent myth about hydration states that caffeine is a diuretic that makes you pee, and therefore caffeinated drinks like coffee and tea don't hydrate your body. The idea is based on the findings of a study from 1928 that looked at three people. Not only is that sample incredibly small by today's standards, but the finding has not held up to more recent experiments. So consider this myth busted.

According to multiple studies, ranging from a 2003 review of research dating back to 1966 to a 2014 clinical trial that compared coffee to water ingestion in 50 men , caffeine can be a mild diuretic in large amounts for people who aren't accustomed to it. But caffeinated drinks consumed in moderation provide the same hydration as non-caffeinated drinks.

"Those studies have shown that drinking caffeinated and some low alcohol-content beverages [such as beer] are not much different than drinking water," says Millard-Stafford of Georgia Tech.

Essentially, with the exception of higher alcohol-content beverages like hard liquor, all liquids count towards hydration. As does food. The experts we spoke to say about 20% of your fluid intake comes from the food you eat, from fruits and vegetables to pasta.

Myth #3: We need sports drinks to replace salt and other electrolytes.

You might hear that you need sports drinks to replace salt and other minerals known as electrolytes (like potassium and chloride, which are also essential for our bodies) when you're active.

If you're exercising for more than an hour or so, it's likely you will need to replace the salt you're sweating out along with water, say the experts. But you don't have to do that by drinking sports drinks like Gatorade. While they can be one effective way to replace the body's salt, you can get that salt from other foods and drinks. And like thirst, you can trust your body to tell you how much you need.

Researchers have found that along with a thirst for water, humans have evolved a thirst for salt and other minerals too. "The brain monitors [how much you lose], then triggers a precise appetite" for something salty, says Oka, the professor of biology at Caltech. That might be sports drinks — or a salty snack like peanuts.

Hew-Butler and a team of colleagues conducted a study to find out just how well the body's thirst mechanism for salt works. They analyzed five years of research on ultra-marathon runners in northern California. Organizers at the races set out tables with salty snacks such as peanuts, pickles, salted watermelon and even salt packets in addition to water, soda and sports drinks and encouraged the runners to consume only what they craved. The researchers found that the runners were able to keep their salt-balance levels in check just by following their thirst and appetite.

Bottom line? Your body will tell you when it's got a hankering for salt — so let your cravings be your guide.

Myth #4: Drinking water can help you lose weight.

Some small studies have found that drinking water before meals can help certain groups of people lose weight. The idea is that water makes your stomach feel full, and therefore, you eat less.

However, there are many conflicting studies on this topic. For example, one paper found that drinking up to 500 mL of water 30 minutes before a meal led to weight loss in a group of young men, but another paper found that the tactic did not work for younger people in the study — only the older ones.

And when scientists looked at papers on this subject in a systematic review, they concluded that there's just not enough evidence for the general public. In a 2013 study published in the American Journal of Clinical Nutrition , researchers surveyed four electronic databases and found that only three studies suggested that increased water consumption could lead to weight loss if it's part of a diet program. But the results were inconsistent for people who were not dieting. Ultimately, the researchers concluded, "The evidence for this association is still low, mostly because of the lack of good-quality studies."

Studies have shown that drinking water can help with weight loss if it's replacing sugary beverages like soda, sweet juices and sports drinks. In a study published in the American Journal of Clinical Nutrition , researchers asked a group of more than 300 overweight and obese individuals to replace such beverages with water for 6 months and found it helped reduce the subjects' weight by an average of 2 to 2.5%.

Myth #5: Dark-colored pee means you're dehydrated.

Scientists commonly measure dehydration by looking at the concentration of sodium and other solids in urine, which is what makes pee darker in color. But that isn't the most precise way to tell whether someone needs more water, says Hew-Butler.

In 2017, she conducted a study published in the journal BMJ Open Sport & Exercise Medicine to see if measuring the salt concentration of urine was an accurate reflection of the salt concentration in blood. She asked 318 athletes to "pee in a cup, then we drew their blood," she says. More than half of the athletes showed up as dehydrated when she measured their urine — but when she looked at their blood, none of them showed up as dehydrated.

Just because your urine is dark gold, says Hew-Butler, it doesn't mean your body is dehydrated. It just means your kidneys aren't releasing as much water in order to keep your blood's water-sodium level balanced. It would be more accurate to look at the concentration of sodium in our blood, she says, because our brain's sensors use that to decide how much water our bodies need.

That said, if you're not great at paying attention to your thirst, some hydration experts recommend drinking enough water to keep your urine a light, straw-yellow color — a simple way to assess hydration.

Hydration, like so many things, comes down to balance.

"It's a happy medium, right?" says Millard-Stafford. "Not too much. Not too little. Just right – the Goldilocks sort of approach."

The audio portion of this episode was produced by Summer Thomad, with help from Sylvie Douglis. The digital story was edited by Malaka Gharib. We'd love to hear from you. Leave us a voicemail at 202-216-9823 , or email us at [email protected] .

• sports drinks

• Search Menu
• Advance articles
• Editor's Choice
• Supplement Archive
• Article Collection Archive
• Author Guidelines
• Submission Site
• Open Access
• Call for Papers
• Why Publish?
• About Nutrition Reviews
• About International Life Sciences Institute
• Editorial Board
• Early Career Editorial Board
• Advertising and Corporate Services
• Journals Career Network
• Self-Archiving Policy
• Journals on Oxford Academic
• Books on Oxford Academic

Article Contents

Introduction, physiological effects of dehydration, hydration and chronic diseases, water consumption and requirements and relationships to total energy intake, water requirements: evaluation of the adequacy of water intake, acknowledgments, water, hydration, and health.

• Article contents
• Figures & tables
• Supplementary Data

Barry M Popkin, Kristen E D'Anci, Irwin H Rosenberg, Water, hydration, and health, Nutrition Reviews , Volume 68, Issue 8, 1 August 2010, Pages 439–458, https://doi.org/10.1111/j.1753-4887.2010.00304.x

• Permissions Icon Permissions

This review examines the current knowledge of water intake as it pertains to human health, including overall patterns of intake and some factors linked with intake, the complex mechanisms behind water homeostasis, and the effects of variation in water intake on health and energy intake, weight, and human performance and functioning. Water represents a critical nutrient, the absence of which will be lethal within days. Water's importance for the prevention of nutrition-related noncommunicable diseases has received more attention recently because of the shift toward consumption of large proportions of fluids as caloric beverages. Despite this focus, there are major gaps in knowledge related to the measurement of total fluid intake and hydration status at the population level; there are also few longer-term systematic interventions and no published randomized, controlled longer-term trials. This review provides suggestions for ways to examine water requirements and encourages more dialogue on this important topic.

Water is essential for life. From the time that primeval species ventured from the oceans to live on land, a major key to survival has been the prevention of dehydration. The critical adaptations cross an array of species, including man. Without water, humans can survive only for days. Water comprises from 75% body weight in infants to 55% in the elderly and is essential for cellular homeostasis and life. 1 Nevertheless, there are many unanswered questions about this most essential component of our body and our diet. This review attempts to provide some sense of our current knowledge of water, including overall patterns of intake and some factors linked with intake, the complex mechanisms behind water homeostasis, the effects of variation in water intake on health and energy intake, weight, and human performance and functioning.

Recent statements on water requirements have been based on retrospective recall of water intake from food and beverages among healthy, noninstitutionalized individuals. Provided here are examples of water intake assessment in populations to clarify the need for experimental studies. Beyond these circumstances of dehydration, it is not fully understood how hydration affects health and well-being, even the impact of water intakes on chronic diseases. Recently, Jéquier and Constant 2 addressed this question based on human physiology, but more knowledge is required about the extent to which water intake might be important for disease prevention and health promotion.

As noted later in the text, few countries have developed water requirements and those that exist are based on weak population-level measures of water intake and urine osmolality. 3 , 4 The European Food Safety Authority (EFSA) was recently asked to revise existing recommended intakes of essential substances with a physiological effect, including water since this nutrient is essential for life and health. 5

The US Dietary Recommendations for water are based on median water intakes with no use of measurements of the dehydration status of the population to assist. One-time collection of blood samples for the analysis of serum osmolality has been used by the National Health and Nutrition Examination Survey program. At the population level, there is no accepted method of assessing hydration status, and one measure some scholars use, hypertonicity, is not even linked with hydration in the same direction for all age groups. 6 Urine indices are used often but these reflect the recent volume of fluid consumed rather than a state of hydration. 7 Many scholars use urine osmolality to measure recent hydration status. 8 , – 12 Deuterium dilution techniques (isotopic dilution with D 2 O, or deuterium oxide) allow measurement of total body water but not water balance status. 13 Currently, there are no completely adequate biomarkers to measure hydration status at the population level.

In discussing water, the focus is first and foremost on all types of water, whether it be soft or hard, spring or well, carbonated or distilled. Furthermore, water is not only consumed directly as a beverage; it is also obtained from food and to a very small extent from oxidation of macronutrients (metabolic water). The proportion of water that comes from beverages and food varies according to the proportion of fruits and vegetables in the diet. The ranges of water content in various foods are presented in Table 1 . In the United States it is estimated that about 22% of water intake comes from food while the percentages are much higher in European countries, particularly a country like Greece with its higher intake of fruits and vegetables, or in South Korea. 3 , – 15 The only in-depth study performed in the United States of water use and water intrinsic to food found a 20.7% contribution from food water; 16 , 17 however, as shown below, this research was dependent on poor overall assessment of water intake.

Ranges of water content for selected foods.

Data from the USDA national nutrient database for standard reference, release 21, as provided in Altman. 126

This review considers water requirements in the context of recent efforts to assess water intake in US populations. The relationship between water and calorie intake is explored both for insights into the possible displacement of calories from sweetened beverages by water and to examine the possibility that water requirements would be better expressed in relation to calorie/energy requirements with the dependence of the latter on age, size, gender, and physical activity level. Current understanding of the exquisitely complex and sensitive system that protects land animals against dehydration is covered and commentary is provided on the complications of acute and chronic dehydration in man, against which a better expression of water requirements might complement the physiological control of thirst. Indeed, the fine intrinsic regulation of hydration and water intake in individuals mitigates prevalent underhydration in populations and its effects on function and disease.

Regulation of fluid intake

To prevent dehydration, reptiles, birds, vertebrates, and all land animals have evolved an exquisitely sensitive network of physiological controls to maintain body water and fluid intake by thirst. Humans may drink for various reasons, particularly for hedonic ones, but drinking is most often due to water deficiency that triggers the so-called regulatory or physiological thirst. The mechanism of thirst is quite well understood today and the reason nonregulatory drinking is often encountered is related to the large capacity of the kidneys to rapidly eliminate excesses of water or to reduce urine secretion to temporarily economize on water. 1 But this excretory process can only postpone the necessity of drinking or of ceasing to drink an excess of water. Nonregulatory drinking is often confusing, particularly in wealthy societies that have highly palatable drinks or fluids that contain other substances the drinker seeks. The most common of these are sweeteners or alcohol for which water is used as a vehicle. Drinking these beverages is not due to excessive thirst or hyperdipsia, as can be shown by offering pure water to individuals instead and finding out that the same drinker is in fact hypodipsic (characterized by abnormally diminished thirst). 1

Fluid balance of the two compartments

Maintaining a constant water and mineral balance requires the coordination of sensitive detectors at different sites in the body linked by neural pathways with integrative centers in the brain that process this information. These centers are also sensitive to humoral factors (neurohormones) produced for the adjustment of diuresis, natriuresis, and blood pressure (angiotensin mineralocorticoids, vasopressin, atrial natriuretic factor). Instructions from the integrative centers to the “executive organs” (kidney, sweat glands, and salivary glands) and to the part of the brain responsible for corrective actions such as drinking are conveyed by certain nerves in addition to the above-mentioned substances. 1

Most of the components of fluid balance are controlled by homeostatic mechanisms responding to the state of body water. These mechanisms are sensitive and precise, and are activated with deficits or excesses of water amounting to only a few hundred milliliters. A water deficit produces an increase in the ionic concentration of the extracellular compartment, which takes water from the intracellular compartment causing cells to shrink. This shrinkage is detected by two types of brain sensors, one controlling drinking and the other controlling the excretion of urine by sending a message to the kidneys, mainly via the antidiuretic hormone vasopressin to produce a smaller volume of more concentrated urine. 18 When the body contains an excess of water, the reverse processes occur: the lower ionic concentration of body fluids allows more water to reach the intracellular compartment. The cells imbibe, drinking is inhibited, and the kidneys excrete more water.

The kidneys thus play a key role in regulating fluid balance. As discussed later, the kidneys function more efficiently in the presence of an abundant water supply. If the kidneys economize on water and produce more concentrated urine, they expend a greater amount of energy and incur more wear on their tissues. This is especially likely to occur when the kidneys are under stress, e.g., when the diet contains excessive amounts of salt or toxic substances that need to be eliminated. Consequently, drinking a sufficient amount of water helps protect this vital organ.

Regulatory drinking

Most drinking occurs in response to signals of water deficit. Apart from urinary excretion, the other main fluid regulatory process is drinking, which is mediated through the sensation of thirst. There are two distinct mechanisms of physiological thirst: the intracellular and the extracellular mechanisms. When water alone is lost, ionic concentration increases. As a result, the intracellular space yields some of its water to the extracellular compartment. Once again, the resulting shrinkage of cells is detected by brain receptors that send hormonal messages to induce drinking. This association with receptors that govern extracellular volume is accompanied by an enhancement of appetite for salt. Thus, people who have been sweating copiously prefer drinks that are relatively rich in Na+ salts rather than pure water. When excessive sweating is experienced, it is also important to supplement drinks with additional salt.

The brain's decision to start or stop drinking and to choose the appropriate drink is made before the ingested fluid can reach the intra- and extracellular compartments. The taste buds in the mouth send messages to the brain about the nature, and especially the salt content, of the ingested fluid, and neuronal responses are triggered as if the incoming water had already reached the bloodstream. These are the so-called anticipatory reflexes: they cannot be entirely “cephalic reflexes” because they arise from the gut as well as the mouth. 1

The anterior hypothalamus and pre-optic area are equipped with osmoreceptors related to drinking. Neurons in these regions show enhanced firing when the inner milieu gets hyperosmotic. Their firing decreases when water is loaded in the carotid artery that irrigates the neurons. It is remarkable that the same decrease in firing in the same neurons takes place when the water load is applied on the tongue instead of being injected into the carotid artery. This anticipatory drop in firing is due to communication from neural pathways that depart from the mouth and converge onto neurons that simultaneously sense the blood's inner milieu.

Nonregulatory drinking

Although everyone experiences thirst from time to time, it plays little role in the day-to-day control of water intake in healthy people living in temperate climates. In these regions, people generally consume fluids not to quench thirst, but as components of everyday foods (e.g., soup, milk), as beverages used as mild stimulants (tea, coffee), and for pure pleasure. A common example is alcohol consumption, which can increase individual pleasure and stimulate social interaction. Drinks are also consumed for their energy content, as in soft drinks and milk, and are used in warm weather for cooling and in cold weather for warming. Such drinking seems to also be mediated through the taste buds, which communicate with the brain in a kind of “reward system”, the mechanisms of which are just beginning to be understood. This bias in the way human beings rehydrate themselves may be advantageous because it allows water losses to be replaced before thirst-producing dehydration takes place. Unfortunately, this bias also carries some disadvantages. Drinking fluids other than water can contribute to an intake of caloric nutrients in excess of requirements, or in alcohol consumption that, in some people, may insidiously bring about dependence. For example, total fluid intake increased from 79 fluid ounces in 1989 to 100 fluid ounces in 2002 among US adults, with the difference representing intake of caloric beverages. 19

Effects of aging on fluid intake regulation

The thirst and fluid ingestion responses of older persons to a number of stimuli have been compared to those of younger persons. 20 Following water deprivation, older individuals are less thirsty and drink less fluid compared to younger persons. 21 , 22 The decrease in fluid consumption is predominantly due to a decrease in thirst, as the relationship between thirst and fluid intake is the same in young and old persons. Older persons drink insufficient amounts of water following fluid deprivation to replenish their body water deficit. 23 When dehydrated older persons are offered a highly palatable selection of drinks, this also fails to result in increased fluid intake. 23 The effects of increased thirst in response to an osmotic load have yielded variable responses, with one group reporting reduced osmotic thirst in older individuals 24 and one failing to find a difference. In a third study, young individuals ingested almost twice as much fluid as old persons, even though the older subjects had a much higher serum osmolality. 25

Overall, these studies support small changes in the regulation of thirst and fluid intake with aging. Defects in both osmoreceptors and baroreceptors appear to exist as do changes in the central regulatory mechanisms mediated by opioid receptors. 26 Because the elderly have low water reserves, it may be prudent for them to learn to drink regularly when not thirsty and to moderately increase their salt intake when they sweat. Better education on these principles may help prevent sudden hypotension and stroke or abnormal fatigue, which can lead to a vicious circle and eventually hospitalization.

Thermoregulation

Hydration status is critical to the body's process of temperature control. Body water loss through sweat is an important cooling mechanism in hot climates and in periods of physical activity. Sweat production is dependent upon environmental temperature and humidity, activity levels, and type of clothing worn. Water losses via skin (both insensible perspiration and sweating) can range from 0.3 L/h in sedentary conditions to 2.0 L/h in high activity in the heat, and intake requirements range from 2.5 to just over 3 L/day in adults under normal conditions, and can reach 6 L/day with high extremes of heat and activity. 27 , 28 Evaporation of sweat from the body results in cooling of the skin. However, if sweat loss is not compensated for with fluid intake, especially during vigorous physical activity, a hypohydrated state can occur with concomitant increases in core body temperature. Hypohydration from sweating results in a loss of electrolytes, as well as a reduction in plasma volume, and this can lead to increased plasma osmolality. During this state of reduced plasma volume and increased plasma osmolality, sweat output becomes insufficient to offset increases in core temperature. When fluids are given to maintain euhydration, sweating remains an effective compensation for increased core temperatures. With repeated exposure to hot environments, the body adapts to heat stress and cardiac output and stroke volume return to normal, sodium loss is conserved, and the risk for heat-stress-related illness is reduced. 29 Increasing water intake during this process of heat acclimatization will not shorten the time needed to adapt to the heat, but mild dehydration during this time may be of concern and is associated with elevations in cortisol, increased sweating, and electrolyte imbalances. 29

Children and the elderly have differing responses to ambient temperature and different thermoregulatory concerns than healthy adults. Children in warm climates may be more susceptible to heat illness than adults due to their greater surface area to body mass ratio, lower rate of sweating, and slower rate of acclimatization to heat. 30 , 31 Children may respond to hypohydration during activity with a higher relative increase in core temperature than adults, 32 and with a lower propensity to sweat, thus losing some of the benefits of evaporative cooling. However, it has been argued that children can dissipate a greater proportion of body heat via dry heat loss, and the concomitant lack of sweating provides a beneficial means of conserving water under heat stress. 30 Elders, in response to cold stress, show impairments in thermoregulatory vasoconstriction, and body water is shunted from plasma into the interstitial and intracellular compartments. 33 , 34 With respect to heat stress, water lost through sweating decreases the water content of plasma, and the elderly are less able to compensate for increased blood viscosity. 33 Not only do they have a physiological hypodipsia, but this can be exaggerated by central nervous system disease 35 and by dementia. 36 In addition, illness and limitations in daily living activities can further limit fluid intake. When reduced fluid intake is coupled with advancing age, there is a decrease in total body water. Older individuals have impaired renal fluid conservation mechanisms and, as noted above, have impaired responses to heat and cold stress. 33 , 34 All of these factors contribute to an increased risk of hypohydration and dehydration in the elderly.

With regard to physiology, the role of water in health is generally characterized in terms of deviations from an ideal hydrated state, generally in comparison to dehydration. The concept of dehydration encompasses both the process of losing body water and the state of dehydration. Much of the research on water and physical or mental functioning compares a euhydrated state, usually achieved by provision of water sufficient to overcome water loss, to a dehydrated state, which is achieved via withholding of fluids over time and during periods of heat stress or high activity. In general, provision of water is beneficial in individuals with a water deficit, but little research supports the notion that additional water in adequately hydrated individuals confers any benefit.

Physical performance

The role of water and hydration in physical activity, particularly in athletes and in the military, has been of considerable interest and is well-described in the scientific literature. 37 , – 39 During challenging athletic events, it is not uncommon for athletes to lose 6–10% of body weight through sweat, thus leading to dehydration if fluids have not been replenished. However, decrements in the physical performance of athletes have been observed under much lower levels of dehydration, i.e., as little as 2%. 38 Under relatively mild levels of dehydration, individuals engaging in rigorous physical activity will experience decrements in performance related to reduced endurance, increased fatigue, altered thermoregulatory capability, reduced motivation, and increased perceived effort. 40 , 41 Rehydration can reverse these deficits and reduce the oxidative stress induced by exercise and dehydration. 42 Hypohydration appears to have a more significant impact on high-intensity and endurance activity, such as tennis 43 and long-distance running, 44 than on anaerobic activities, 45 such as weight lifting, or on shorter-duration activities, such as rowing. 46

During exercise, individuals may not hydrate adequately when allowed to drink according to thirst. 32 After periods of physical exertion, voluntary fluid intake may be inadequate to offset fluid deficits. 1 Thus, mild-to-moderate dehydration can persist for some hours after the conclusion of physical activity. Research performed on athletes suggests that, principally at the beginning of the training season, they are at particular risk for dehydration due to lack of acclimatization to weather conditions or suddenly increased activity levels. 47 , 48 A number of studies show that performance in temperate and hot climates is affected to a greater degree than performance in cold temperatures. 41 , – 50 Exercise in hot conditions with inadequate fluid replacement is associated with hyperthermia, reduced stroke volume and cardiac output, decreases in blood pressure, and reduced blood flow to muscle. 51

During exercise, children may be at greater risk for voluntary dehydration. Children may not recognize the need to replace lost fluids, and both children as well as coaches need specific guidelines for fluid intake. 52 Additionally, children may require more time to acclimate to increases in environmental temperature than adults. 30 , 31 Recommendations are for child athletes or children in hot climates to begin athletic activities in a well-hydrated state and to drink fluids over and above the thirst threshold.

Cognitive performance

Water, or its lack (dehydration), can influence cognition. Mild levels of dehydration can produce disruptions in mood and cognitive functioning. This may be of special concern in the very young, very old, those in hot climates, and those engaging in vigorous exercise. Mild dehydration produces alterations in a number of important aspects of cognitive function such as concentration, alertness, and short-term memory in children (10–12 y), 32 young adults (18–25 y), 53 , – 56 and the oldest adults (50–82 y). 57 As with physical functioning, mild-to-moderate levels of dehydration can impair performance on tasks such as short-term memory, perceptual discrimination, arithmetic ability, visuomotor tracking, and psychomotor skills. 53 , – 56 However, mild dehydration does not appear to alter cognitive functioning in a consistent manner. 53 , – 58 In some cases, cognitive performance was not significantly affected in ranges from 2% to 2.6% dehydration. 56 , 58 Comparing across studies, performance on similar cognitive tests was divergent under dehydration conditions. 54 , 56 In studies conducted by Cian et al., 53 , 54 participants were dehydrated to approximately 2.8% either through heat exposure or treadmill exercise. In both studies, performance was impaired on tasks examining visual perception, short-term memory, and psychomotor ability. In a series of studies using exercise in conjunction with water restriction as a means of producing dehydration, D'Anci et al. 56 observed only mild decrements in cognitive performance in healthy young men and women athletes. In these experiments, the only consistent effect of mild dehydration was significant elevations of subjective mood score, including fatigue, confusion, anger, and vigor. Finally, in a study using water deprivation alone over a 24-h period, no significant decreases in cognitive performance were seen with 2.6% dehydration. 58 It is therefore possible that heat stress may play a critical role in the effects of dehydration on cognitive performance.

Reintroduction of fluids under conditions of mild dehydration can reasonably be expected to reverse dehydration-induced cognitive deficits. Few studies have examined how fluid reintroduction may alleviate the negative effects of dehydration on cognitive performance and mood. One study 59 examined how water ingestion affected arousal and cognitive performance in young people following a period of 12-h water restriction. While cognitive performance was not affected by either water restriction or water consumption, water ingestion affected self-reported arousal. Participants reported increased alertness as a function of water intake. Rogers et al. 60 observed a similar increase in alertness following water ingestion in both high- and low-thirst participants. Water ingestion, however, had opposite effects on cognitive performance as a function of thirst. High-thirst participants' performance on a cognitively demanding task improved following water ingestion, but low-thirst participants' performance declined. In summary, hydration status consistently affected self-reported alertness, but effects on cognition were less consistent.

Several recent studies have examined the utility of providing water to school children on attentiveness and cognitive functioning in children. 61 , – 63 In these experiments, children were not fluid restricted prior to cognitive testing, but were allowed to drink as usual. Children were then provided with a drink or no drink 20–45 min before the cognitive test sessions. In the absence of fluid restriction and without physiological measures of hydration status, the children in these studies should not be classified as dehydrated. Subjective measures of thirst were reduced in children given water, 62 and voluntary water intake in children varied from 57 mL to 250 mL. In these studies, as in the studies in adults, the findings were divergent and relatively modest. In the research led by Edmonds et al., 61 , 62 children in the groups given water showed improvements in visual attention. However, effects on visual memory were less consistent, with one study showing no effects of drinking water on a spot-the-difference task in 6–7-year-old children 61 and the other showing a significant improvement in a similar task in 7–9-year-old children. 62 In the research described by Benton and Burgess, 63 memory performance was improved by provision of water but sustained attention was not altered with provision of water in the same children.

Taken together, these studies indicate that low-to-moderate dehydration may alter cognitive performance. Rather than indicating that the effects of hydration or water ingestion on cognition are contradictory, many of the studies differ significantly in methodology and in measurement of cognitive behaviors. These variances in methodology underscore the importance of consistency when examining relatively subtle chances in overall cognitive performance. However, in those studies in which dehydration was induced, most combined heat and exercise; this makes it difficult to disentangle the effects of dehydration on cognitive performance in temperate conditions from the effects of heat and exercise. Additionally, relatively little is known about the mechanism of mild dehydration's effects on mental performance. It has been proposed that mild dehydration acts as a physiological stressor that competes with and draws attention from cognitive processes. 64 However, research on this hypothesis is limited and merits further exploration.

Dehydration and delirium

Dehydration is a risk factor for delirium and for delirium presenting as dementia in the elderly and in the very ill. 65 , – 67 Recent work shows that dehydration is one of several predisposing factors for confusion observed in long-term-care residents 67 ; however, in this study, daily water intake was used as a proxy measure for dehydration rather than other, more direct clinical assessments such as urine or plasma osmolality. Older people have been reported as having reduced thirst and hypodipsia relative to younger people. In addition, fluid intake and maintenance of water balance can be complicated by factors such as disease, dementia, incontinence, renal insufficiency, restricted mobility, and drug side effects. In response to primary dehydration, older people have less thirst sensation and reduced fluid intakes in comparison to younger people. However, in response to heat stress, while older people still display a reduced thirst threshold, they do ingest comparable amounts of fluid to younger people. 20

Gastrointestinal function

Fluids in the diet are generally absorbed in the proximal small intestine, and the absorption rate is determined by the rate of gastric emptying to the small intestine. Therefore, the total volume of fluid consumed will eventually be reflected in water balance, but the rate at which rehydration occurs is dependent upon factors affecting the rate of delivery of fluids to the intestinal mucosa. The gastric emptying rate is generally accelerated by the total volume consumed and slowed by higher energy density and osmolality. 68 In addition to water consumed in food (1 L/day) and beverages (circa 2–3 L/day), digestive secretions account for a far greater portion of water that passes through and is absorbed by the gastrointestinal tract (circa 8 L/day). 69 The majority of this water is absorbed by the small intestine, with a capacity of up to 15 L/day with the colon absorbing some 5 L/day. 69

Constipation, characterized by slow gastrointestinal transit, small, hard stools, and difficulty in passing stool, has a number of causes, including medication use, inadequate fiber intake, poor diet, and illness. 70 Inadequate fluid consumption is touted as a common culprit in constipation, and increasing fluid intake is a frequently recommended treatment. Evidence suggests, however, that increasing fluids is only useful to individuals in a hypohydrated state, and is of little utility in euhydrated individuals. 70 In young children with chronic constipation, increasing daily water intake by 50% did not affect constipation scores. 71 For Japanese women with low fiber intake, concomitant low water intake in the diet is associated with increased prevalence of constipation. 72 In older individuals, low fluid intake is a predictor for increased levels of acute constipation, 73 , 74 with those consuming the least amount of fluid having over twice the frequency of constipation episodes than those consuming the most fluid. In one trial, researchers compared the utility of carbonated mineral water in reducing functional dyspepsia and constipation scores to tap water in individuals with functional dyspepsia. 75 When comparing carbonated mineral water to tap water, participants reported improvements in subjective gastric symptoms, but there were no significant improvements in gastric or intestinal function. The authors indicate it is not possible to determine to what degree the mineral content of the two waters contributed to perceived symptom relief, as the mineral water contained greater levels of magnesium and calcium than the tap water. The available evidence suggests that increased fluid intake should only be indicated in individuals in a hypohydrated state. 69 , 71

Significant water loss can occur through the gastrointestinal tract, and this can be of great concern in the very young. In developing countries, diarrheal diseases are a leading cause of death in children, resulting in approximately 1.5–2.5 million deaths per year. 76 Diarrheal illness results not only in a reduction in body water, but also in potentially lethal electrolyte imbalances. Mortality in such cases can many times be prevented with appropriate oral rehydration therapy, by which simple dilute solutions of salt and sugar in water can replace fluid lost by diarrhea. Many consider application of oral rehydration therapy to be one of the significant public health developments of the last century. 77

Kidney function

As noted above, the kidney is crucial in regulating water balance and blood pressure as well as removing waste from the body. Water metabolism by the kidney can be classified into regulated and obligate. Water regulation is hormonally mediated, with the goal of maintaining a tight range of plasma osmolality (between 275 and 290 mOsm/kg). Increases in plasma osmolality and activation of osmoreceptors (intracellular) and baroreceptors (extracellular) stimulate hypothalamic release of arginine vasopressin (AVP). AVP acts at the kidney to decrease urine volume and promote retention of water, and the urine becomes hypertonic. With decreased plasma osmolality, vasopressin release is inhibited, and the kidney increases hypotonic urinary output.

In addition to regulating fluid balance, the kidneys require water for the filtration of waste from the bloodstream and excretion via urine. Water excretion via the kidney removes solutes from the blood, and a minimum obligate urine volume is required to remove the solute load with a maximum output volume of 1 L/h. 78 This obligate volume is not fixed, but is dependent upon the amount of metabolic solutes to be excreted and levels of AVP. Depending on the need for water conservation, basal urine osmolality ranges from 40 mOsm/kg to a maximum of 1,400 mOsm/kg. 78 The ability to both concentrate and dilute urine decreases with age, with a lower value of 92 mOsm/kg and an upper range falling between 500 and 700 mOsm/kg for individuals over the age of 70 years. 79 , – 81 Under typical conditions, in an average adult, urine volume of 1.5 to 2.0 L/day would be sufficient to clear a solute load of 900 to 1,200 mOsm/day. During water conservation and the presence of AVP, this obligate volume can decrease to 0.75–1.0 L/day and during maximal diuresis up to 20 L/day can be required to remove the same solute load. 78 , – 81 In cases of water loading, if the volume of water ingested cannot be compensated for with urine output, having overloaded the kidney's maximal output rate, an individual can enter a hyponatremic state.

Heart function and hemodynamic response

Blood volume, blood pressure, and heart rate are closely linked. Blood volume is normally tightly regulated by matching water intake and water output, as described in the section on kidney function. In healthy individuals, slight changes in heart rate and vasoconstriction act to balance the effect of normal fluctuations in blood volume on blood pressure. 82 Decreases in blood volume can occur, through blood loss (or blood donation), or loss of body water through sweat, as seen with exercise. Blood volume is distributed differently relative to the position of the heart, whether supine or upright, and moving from one position to the other can lead to increased heart rate, a fall in blood pressure, and, in some cases, syncope. This postural hypotension (or orthostatic hypotension) can be mediated by drinking 300–500 mL of water. 83 , 84 Water intake acutely reduces heart rate and increases blood pressure in both normotensive and hypertensive individuals. 85 These effects of water intake on the pressor effect and heart rate occur within 15–20 min of drinking water and can last for up to 60 min. Water ingestion is also beneficial in preventing vasovagal reaction with syncope in blood donors at high risk for post-donation syncope. 86 The effect of water intake in these situations is thought to be due to effects on the sympathetic nervous system rather than to changes in blood volume. 83 , 84 Interestingly, in rare cases, individuals may experience bradycardia and syncope after swallowing cold liquids. 87 , – 89 While swallow syncope can be seen with substances other than water, swallow syncope further supports the notion that the result of water ingestion in the pressor effect has both a neural component as well as a cardiac component.

Water deprivation and dehydration can lead to the development of headache. 90 Although this observation is largely unexplored in the medical literature, some observational studies indicate that water deprivation, in addition to impairing concentration and increasing irritability, can serve as a trigger for migraine and can also prolong migraine. 91 , 92 In those with water deprivation-induced headache, ingestion of water provided relief from headache in most individuals within 30 min to 3 h. 92 It is proposed that water deprivation-induced headache is the result of intracranial dehydration and total plasma volume. Although provision of water may be useful in relieving dehydration-related headache, the utility of increasing water intake for the prevention of headache is less well documented.

The folk wisdom that drinking water can stave off headaches has been relatively unchallenged, and has more traction in the popular press than in the medical literature. Recently, one study examined increased water intake and headache symptoms in headache patients. 93 In this randomized trial, patients with a history of different types of headache, including migraine and tension headache, were either assigned to a placebo condition (a nondrug tablet) or the increased water condition. In the water condition, participants were instructed to consume an additional volume of 1.5 L water/day on top of what they already consumed in foods and fluids. Water intake did not affect the number of headache episodes, but it was modestly associated with reduction in headache intensity and reduced duration of headache. The data from this study suggest that the utility of water as prophylaxis is limited in headache sufferers, and the ability of water to reduce or prevent headache in the broader population remains unknown.

One of the more pervasive myths regarding water intake is its relation to improvements of the skin or complexion. By improvement, it is generally understood that individuals are seeking to have a more “moisturized” look to the surface skin, or to minimize acne or other skin conditions. Numerous lay sources such as beauty and health magazines as well as postings on the Internet suggest that drinking 8–10 glasses of water a day will “flush toxins from the skin” and “give a glowing complexion” despite a general lack of evidence 94 , 95 to support these proposals. The skin, however, is important for maintaining body water levels and preventing water loss into the environment.

The skin contains approximately 30% water, which contributes to plumpness, elasticity, and resiliency. The overlapping cellular structure of the stratum corneum and lipid content of the skin serves as “waterproofing” for the body. 96 Loss of water through sweat is not indiscriminate across the total surface of the skin, but is carried out by eccrine sweat glands, which are evenly distributed over most of the body surface. 97 Skin dryness is usually associated with exposure to dry air, prolonged contact with hot water and scrubbing with soap (both strip oils from the skin), medical conditions, and medications. While more serious levels of dehydration can be reflected in reduced skin turgor, 98 , 99 with tenting of the skin acting as a flag for dehydration, overt skin turgor in individuals with adequate hydration is not altered. Water intake, particularly in individuals with low initial water intake, can improve skin thickness and density as measured by sonogram, 100 offsets transepidermal water loss, and can improve skin hydration. 101 Adequate skin hydration, however, is not sufficient to prevent wrinkles or other signs of aging, which are related to genetics and to sun and environmental damage. Of more utility to individuals already consuming adequate fluids is the use of topical emollients; these will improve skin barrier function and improve the look and feel of dry skin. 102 , 103

Many chronic diseases have multifactorial origins. In particular, differences in lifestyle and the impact of environment are known to be involved and constitute risk factors that are still being evaluated. Water is quantitatively the most important nutrient. In the past, scientific interest with regard to water metabolism was mainly directed toward the extremes of severe dehydration and water intoxication. There is evidence, however, that mild dehydration may also account for some morbidities. 4 , 104 There is currently no consensus on a “gold standard” for hydration markers, particularly for mild dehydration. As a consequence, the effects of mild dehydration on the development of several disorders and diseases have not been well documented.

There is strong evidence showing that good hydration reduces the risk of urolithiasis (see Table 2 for evidence categories). Less strong evidence links good hydration with reduced incidence of constipation, exercise asthma, hypertonic dehydration in the infant, and hyperglycemia in diabetic ketoacidosis. Good hydration is associated with a reduction in urinary tract infections, hypertension, fatal coronary heart disease, venous thromboembolism, and cerebral infarct, but all these effects need to be confirmed by clinical trials. For other conditions such as bladder or colon cancer, evidence of a preventive effect of maintaining good hydration is not consistent (see Table 3 ).

Categories of evidence used in evaluating the quality of reports.

Data adapted from Manz. 104

Summary of evidence for association of hydration status with chronic diseases.

Categories of evidence: described in Table 2 .

Water consumption, water requirements, and energy intake are linked in fairly complex ways. This is partially because physical activity and energy expenditures affect the need for water but also because a large shift in beverage consumption over the past century or more has led to consumption of a significant proportion of our energy intake from caloric beverages. Nonregulatory beverage intake, as noted earlier, has assumed a much greater role for individuals. 19 This section reviews current patterns of water intake and then refers to a full meta-analysis of the effects of added water on energy intake. This includes adding water to the diet and water replacement for a range of caloric and diet beverages, including sugar-sweetened beverages, juice, milk, and diet beverages. The third component is a discussion of water requirements and suggestions for considering the use of mL water/kcal energy intake as a metric.

Patterns and trends of water consumption

Measurement of total fluid water consumption in free-living individuals is fairly new in focus. As a result, the state of the science is poorly developed, data are most likely fairly incomplete, and adequate validation of the measurement techniques used is not available. Presented here are varying patterns and trends of water intake for the United States over the past three decades followed by a brief review of the work on water intake in Europe.

There is really no existing information to support an assumption that consumption of water alone or beverages containing water affects hydration differentially. 3 , 105 Some epidemiological data suggest water might have different metabolic effects when consumed alone rather than as a component of caffeinated or flavored or sweetened beverages; however, these data are at best suggestive of an issue deserving further exploration. 106 , 107 As shown below, the research of Ershow et al. indicates that beverages not consisting solely of water do contain less than 100% water.

One study in the United States has attempted to examine all the dietary sources of water. 16 , 17 These data are cited in Table 4 as the Ershow study and were based on National Food Consumption Survey food and fluid intake data from 1977–1978. These data are presented in Table 4 for children aged 2–18 years (Panel A) and for adults aged 19 years and older (Panel B). Ershow et al. 16 , 17 spent a great deal of time working out ways to convert USDA dietary data into water intake, including water absorbed during the cooking process, water in food, and all sources of drinking water.

Beverage pattern trends in the United States for children aged 2–18 years and adults aged 19 years and older, (nationally representative).

Note: The data are age and sex adjusted to 1965.

Values stem from the Ershow calculations. 16

These researchers created a number of categories and used a range of factors measured in other studies to estimate the water categories. The water that is found in food, based on food composition table data, was 393 mL for children. The water that was added as a result of cooking (e.g., rice) was 95 mL. Water consumed as a beverage directly as water was 624 mL. The water found in other fluids, as noted, comprised the remainder of the milliliters, with the highest levels in whole-fat milk and juices (506 mL). There is a small discrepancy between the Ershow data regarding total fluid intake measures for these children and the normal USDA figures. That is because the USDA does not remove milk fats and solids, fiber, and other food constituents found in beverages, particularly juice and milk.

A key point illustrated by these nationally representative US data is the enormous variability between survey waves in the amount of water consumed (see Figure 1 , which highlights the large variation in water intake as measured in these surveys). Although water intake by adults and children increased and decreased at the same time, for reasons that cannot be explained, the variation was greater among children than adults. This is partly because the questions the surveys posed varied over time and there was no detailed probing for water intake, because the focus was on obtaining measures of macro- and micronutrients. Dietary survey methods used in the past have focused on obtaining data on foods and beverages containing nutrient and non-nutritive sweeteners but not on water. Related to this are the huge differences between the the USDA surveys and the National Health and Nutrition Examination Survey (NHANES) performed in 1988–1994 and in 1999 and later. In addition, even the NHANES 1999–2002 and 2003–2006 surveys differ greatly. These differences reflect a shift in the mode of questioning with questions on water intake being included as part of a standard 24-h recall rather than as stand-alone questions. Water intake was not even measured in 1965, and a review of the questionnaires and the data reveals clear differences in the way the questions have been asked and the limitations on probes regarding water intake. Essentially, in the past people were asked how much water they consumed in a day and now they are asked for this information as part of a 24-h recall survey. However, unlike for other caloric and diet beverages, there are limited probes for water alone. The results must thus be viewed as crude approximations of total water intake without any strong research to show if they are over- or underestimated. From several studies of water and two ongoing randomized controlled trials performed by us, it is clear that probes that include consideration of all beverages and include water as a separate item result in the provision of more complete data.

Water consumption trends from USDA and NHANES surveys (mL/day/capita), nationally representative. Note: this includes water from fluids only, excluding water in foods. Sources for 1965, 1977–1978, 1989–1991, and 1994–1998, are USDA. Others are NHANES and 2005–2006 is joint USDA and NHANES.

Water consumption data for Europe are collected far more selectively than even the crude water intake questions from NHANES. A recent report from the European Food Safety Agency provides measures of water consumption from a range of studies in Europe. 4 , – 109 Essentially, what these studies show is that total water intake is lower across Europe than in the United States. As with the US data, none are based on long-term, carefully measured or even repeated 24-h recall measures of water intake from food and beverages. In an unpublished examination of water intake in UK adults in 1986–1987 and in 2001–2002, Popkin and Jebb have found that although intake increased by 226 mL/day over this time period, it was still only 1,787 mL/day in the latter period (unpublished data available from BP); this level is far below the 2,793 mL/day recorded in the United States for 2005–2006 or the earlier US figures for comparably aged adults.

A few studies have been performed in the United States and Europe utilizing 24-h urine and serum osmolality measures to determine total water turnover and hydration status. Results of these studies suggest that US adults consume over 2,100 mL of water per day while adults in Europe consume less than half a liter. 4 , 110 Data on total urine collection would appear to be another useful measure for examining total water intake. Of course, few studies aside from the Donald Study of an adolescent cohort in Germany have collected such data on population levels for large samples. 109

Effects of water consumption on overall energy intake

There is an extensive body of literature that focuses on the impact of sugar-sweetened beverages on weight and the risk of obesity, diabetes, and heart disease; however, the perspective of providing more water and its impact on health has not been examined. The literature on water does not address portion sizes; instead, it focuses mainly on water ad libitum or in selected portions compared with other caloric beverages. A detailed meta-analysis of the effects of water intake alone (i.e., adding additional water) and as a replacement for sugar-sweetened beverages, juice, milk, and diet beverages appears elsewhere. 111

In general, the results of this review suggest that water, when consumed in place of sugar-sweetened beverages, juice, and milk, is linked with reduced energy intake. This finding is mainly derived from clinical feeding studies but also from one very good randomized, controlled school intervention and several other epidemiological and intervention studies. Aside from the issue of portion size, factors such as the timing of beverage and meal intake (i.e., the delay between consumption of the beverage and consumption of the meal) and types of caloric sweeteners remain to be considered. However, when beverages are consumed in normal free-living conditions in which five to eight daily eating occasions are the norm, the delay between beverage and meal consumption may matter less. 112 , – 114

The literature on the water intake of children is extremely limited. However, the excellent German school intervention with water suggests the effects of water on the overall energy intake of children might be comparable to that of adults. 115 In this German study, children were educated on the value of water and provided with special filtered drinking fountains and water bottles in school. The intervention schoolchildren increased their water intake by 1.1 glasses/day ( P  < 0.001) and reduced their risk of overweight by 31% (OR = 0.69, P  = 0.40).

Classically, water data are examined in terms of milliliters (or some other measure of water volume consumed per capita per day by age group). This measure does not link fluid intake and caloric intake. Disassociation of fluid and calorie intake is difficult for clinicians dealing with older persons with reduced caloric intake. This milliliter water measure assumes some mean body size (or surface area) and a mean level of physical activity – both of which are determinants of not only energy expenditure but also water balance. Children are dependent on adults for access to water, and studies suggest that their larger surface area to volume ratio makes them susceptible to changes in skin temperatures linked with ambient temperature shifts. 116 One option utilized by some scholars is to explore food and beverage intake in milliliters per kilocalorie (mL/kcal), as was done in the 1989 US recommended dietary allowances. 4 , 117 This is an option that is interpretable for clinicians and which incorporates, in some sense, body size or surface area and activity. Its disadvantage is that water consumed with caloric beverages affects both the numerator and the denominator; however, an alternative measure that could be independent of this direct effect on body weight and/or total caloric intake is not presently known.

Despite its critical importance in health and nutrition, the array of available research that serves as a basis for determining requirements for water or fluid intake, or even rational recommendations for populations, is limited in comparison with most other nutrients. While this deficit may be partly explained by the highly sensitive set of neurophysiological adaptations and adjustments that occur over a large range of fluid intakes to protect body hydration and osmolarity, this deficit remains a challenge for the nutrition and public health community. The latest official effort at recommending water intake for different subpopulations occurred as part of the efforts to establish Dietary Reference Intakes in 2005, as reported by the Institute of Medicine of the National Academies of Science. 3 As a graphic acknowledgment of the limited database upon which to express estimated average requirements for water for different population groups, the Committee and the Institute of Medicine stated: “While it might appear useful to estimate an average requirement (an EAR) for water, an EAR based on data is not possible.” Given the extreme variability in water needs that are not solely based on differences in metabolism, but also on environmental conditions and activities, there is not a single level of water intake that would assure adequate hydration and optimum health for half of all apparently healthy persons in all environmental conditions. Thus, an adequate intake (AI) level was established in place of an EAR for water.

The AIs for different population groups were set as the median water intakes for populations, as reported in the National Health and Nutrition Examination Surveys; however, the intake levels reported in these surveys varied greatly based on the survey years (e.g., NHANES 1988–1994 versus NHANES 1999–2002) and were also much higher than those found in the USDA surveys (e.g., 1989–1991, 1994–1998, or 2005–2006). If the AI for adults, as expressed in Table 5 , is taken as a recommended intake, the wisdom of converting an AI into a recommended water or fluid intake seems questionable. The first problem is the almost certain inaccuracy of the fluid intake information from the national surveys, even though that problem may also exist for other nutrients. More importantly, from the standpoint of translating an AI into a recommended fluid intake for individuals or populations, is the decision that was made when setting the AI to add an additional roughly 20% of water intake, which is derived from some foods in addition to water and beverages. While this may have been a legitimate effort to use total water intake as a basis for setting the AI, the recommendations that derive from the IOM report would be better directed at recommendations for water and other fluid intake on the assumption that the water content of foods would be a “passive” addition to total water intake. In this case, the observations of the dietary reference intake committee that it is necessary for water intake to meet needs imposed by metabolism and environmental conditions must be extended to consider three added factors, namely body size, gender, and physical activity. Those are the well-studied factors that allow a rather precise measurement and determination of energy intake requirements. It is, therefore, logical that those same factors might underlie recommendations to meet water intake needs in the same populations and individuals. Consideration should also be given to the possibility that water intake needs would best be expressed relative to the calorie requirements, as is done regularly in the clinical setting, and data should be gathered to this end through experimental and population research.

Water requirements expressed in relation to energy recommendations.

AI for total fluids derived from dietary reference intakes for water, potassium, sodium, chloride, and sulphate.

Ratios for water intake based on the AI for water in liters/day calculated using EER for each range of physical activity. EER adapted from the Institute of Medicine Dietary Reference Intakes Macronutrients Report, 2002.

It is important to note that only a few countries include water on their list of nutrients. 118 The European Food Safety Authority is developing a standard for all of Europe. 105 At present, only the United States and Germany provide AI values for water. 3 , 119

Another approach to the estimation of water requirements, beyond the limited usefulness of the AI or estimated mean intake, is to express water intake requirements in relation to energy requirements in mL/kcal. An argument for this approach includes the observation that energy requirements for each age and gender group are strongly evidence-based and supported by extensive research taking into account both body size and activity level, which are crucial determinants of energy expenditure that must be met by dietary energy intake. Such measures of expenditure have used highly accurate methods, such as doubly labeled water; thus, estimated energy requirements have been set based on solid data rather than the compromise inherent in the AIs for water. Those same determinants of energy expenditure and recommended intake are also applicable to water utilization and balance, and this provides an argument for pegging water/fluid intake recommendations to the better-studied energy recommendations. The extent to which water intake and requirements are determined by energy intake and expenditure is understudied, but in the clinical setting it has long been practice to supply 1 mL/kcal administered by tube to patients who are unable to take in food or fluids. Factors such as fever or other drivers of increased metabolism affect both energy expenditure and fluid loss and are thus linked in clinical practice. This concept may well deserve consideration in the setting of population intake goals.

Finally, for decades there has been discussion about expressing nutrient requirements per 1,000 kcal so that a single number would apply reasonably across the spectrum of age groups. This idea, which has never been adopted by the Institute of Medicine and the National Academies of Science, may lend itself to an improved expression of water/fluid intake requirements, which must eventually replace the AIs. Table 5 presents the IOM water requirements and then develops a ratio of mL/kcal based on them. The European Food Safety Agency refers positively to the possibility of expressing water intake recommendations in mL/kcal as a function of energy requirements. 105 Outliers in the adult male categories, which reach ratios as high as 1.5, may well be based on the AI data from the United States, which are above those in the more moderate and likely more accurate European recommendations.

The topic of utilizing mL/kcal to examine water intake and water gaps is explored in Table 6 , which takes the full set of water intake AIs for each age-gender grouping and examines total intake. The data suggest a high level of fluid deficiency. Since a large proportion of fluids in the United States is based on caloric beverages and this proportion has changed markedly over the past 30 years, fluid intake increases both the numerator and the denominator of this mL/kcal relationship. Nevertheless, even using 1 mL/kcal as the AI would leave a gap for all children and adolescents. The NHANES physical activity data were also translated into METS/day to categorize all individuals by physical activity level and thus varying caloric requirements. Use of these measures reveals a fairly large fluid gap, particularly for adult males as well as children ( Table 6 ).

Water intake and water intake gaps based on US Water Adequate Intake Recommendations (based on utilization of water and physical activity data from NHANES 2005–2006).

Note: Recommended water intake for actual activity level is the upper end of the range for moderate and active.

A weighted average for the proportion of individuals in each METS-based activity level.

This review has pointed out a number of issues related to water, hydration, and health. Since water is undoubtedly the most important nutrient and the only one for which an absence will prove lethal within days, understanding of water measurement and water requirements is very important. The effects of water on daily performance and short- and long-term health are quite clear. The existing literature indicates there are few negative effects of water intake while the evidence for positive effects is quite clear.

Little work has been done to measure total fluid intake systematically, and there is no understanding of measurement error and best methods of understanding fluid intake. The most definitive US and European documents on total water requirements are based on these extant intake data. 3 , 105 The absence of validation methods for water consumption intake levels and patterns represents a major gap in knowledge. Even varying the methods of probing in order to collect better water recall data has been little explored.

On the other side of the issue is the need to understand total hydration status. There are presently no acceptable biomarkers of hydration status at the population level, and controversy exists about the current knowledge of hydration status among older Americans. 6 , 120 Thus, while scholars are certainly focused on attempting to create biomarkers for measuring hydration status at the population level, the topic is currently understudied.

As noted, the importance of understanding the role of fluid intake on health has emerged as a topic of increasing interest, partially because of the trend toward rising proportions of fluids being consumed in the form of caloric beverages. The clinical, epidemiological, and intervention literature on the effects of added water on health are covered in a related systematic review. 111 The use of water as a replacement for sugar-sweetened beverages, juice, or whole milk has clear effects in that energy intake is reduced by about 10–13% of total energy intake. However, only a few longer-term systematic interventions have investigated this topic and no randomized, controlled, longer-term trials have been published to date. There is thus very minimal evidence on the effects of just adding water to the diet and of replacing water with diet beverages.

There are many limitations to this review. One certainly is the lack of discussion of potential differences in the metabolic functioning of different types of beverages. 121 Since the literature in this area is sparse, however, there is little basis for delving into it at this point. A discussion of the potential effects of fructose (from all caloric sweeteners when consumed in caloric beverages) on abdominal fat and all of the metabolic conditions directly linked with it (e.g., diabetes) is likewise lacking. 122 , – 125 A further limitation is the lack of detailed review of the array of biomarkers being considered to measure hydration status. Since there is no measurement in the field today that covers more than a very short time period, except for 24-hour total urine collection, such a discussion seems premature.

Some ways to examine water requirements have been suggested in this review as a means to encourage more dialogue on this important topic. Given the significance of water to our health and of caloric beverages to our total energy intake, as well as the potential risks of nutrition-related noncommunicable diseases, understanding both the requirements for water in relation to energy requirements, and the differential effects of water versus other caloric beverages, remain important outstanding issues.

This review has attempted to provide some sense of the importance of water to our health, its role in relationship to the rapidly increasing rates of obesity and other related diseases, and the gaps in present understanding of hydration measurement and requirements. Water is essential to our survival. By highlighting its critical role, it is hoped that the focus on water in human health will sharpen.

The authors wish to thank Ms. Frances L. Dancy for administrative assistance, Mr. Tom Swasey for graphics support, Dr. Melissa Daniels for assistance, and Florence Constant (Nestle's Water Research) for advice and references.

This work was supported by the Nestlé Waters, Issy-les-Moulineaux, France, 5ROI AGI0436 from the National Institute on Aging Physical Frailty Program, and NIH R01-CA109831 and R01-CA121152.

Declaration of interest

The authors have no relevant interests to declare.

Nicolaidis S . Physiology of thirst . In: Arnaud MJ , ed. Hydration Throughout Life . Montrouge: John Libbey Eurotext ; 1998 : 247 .

Google Scholar

Jequier E Constant F . Water as an essential nutrient: the physiological basis of hydration . Eur J Clin Nutr. 2010 ; 64 : 115 – 123 .

Institute of Medicine . Panel on Dietary Reference Intakes for Electrolytes and Water. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate . Washington, DC: The National Academies Press ; 2005 .

Manz F Wentz A . Hydration status in the United States and Germany . Nutr Rev. 2005 ; 63 :(Suppl): S55 – S62 .

European Food Safety Authority . Scientific opinion of the Panel on Dietetic Products Nutrition and Allergies. Draft dietary reference values for water . EFSA J. 2008 : 2 – 49 .

Stookey JD . High prevalence of plasma hypertonicity among community-dwelling older adults: results from NHANES III . J Am Diet Assoc. 2005 ; 105 : 1231 – 1239 .

Armstrong LE . Hydration assessment techniques . Nutr Rev. 2005 ; 63 (Suppl): S40 – S54 .

Bar-David Y Urkin J Kozminsky E . The effect of voluntary dehydration on cognitive functions of elementary school children . Acta Paediatr. 2005 ; 94 : 1667 – 1673 .

Shirreffs S . Markers of hydration status . J Sports Med Phys Fitness. 2000 ; 40 : 80 – 84 .

Popowski L Oppliger R Lambert G Johnson R Johnson A Gisolfi C . Blood and urinary measures of hydration status during progressive acute dehydration . Med Sci Sports Exerc. 2001 ; 33 : 747 – 753 .

Bar-David Y Landau D Bar-David Z Pilpel D Philip M . Urine osmolality among elementary schoolchildren living in a hot climate: implications for dehydration . Ambulatory Child Health. 1998 ; 4 : 393 – 397 .

Fadda R Rapinett G Grathwohl D Parisi M Fanari R Schmitt J . The Benefits of Drinking Supplementary Water at School on Cognitive Performance in Children . Washington, DC: International Society for Developmental Psychobiology ; 2008 : Abstract from poster session at the 41st Annual Conference of International Society for Psychobiology. Abstracts published in: Developmental Psychobiology 2008: v. 50(7): 726 . http://www3.interscience.wiley.com/cgi-bin/fulltext/121421361/PDFSTART

Eckhardt CL Adair LS Caballero B , et al . Estimating body fat from anthropometry and isotopic dilution: a four-country comparison . Obes Res. 2003 ; 11 : 1553 – 1562 .

Moreno LA Sarria A Popkin BM . The nutrition transition in Spain: a European Mediterranean country . Eur J Clin Nutr. 2002 ; 56 : 992 – 1003 .

Lee MJ Popkin BM Kim S . The unique aspects of the nutrition transition in South Korea: the retention of healthful elements in their traditional diet . Public Health Nutr. 2002 ; 5 : 197 – 203 .

Ershow AG Brown LM Cantor KP . Intake of tapwater and total water by pregnant and lactating women . Am J Public Health. 1991 ; 81 : 328 – 334 .

Ershow AG Cantor KP . Total Water and Tapwater Intake in the United States: Population-Based Estimates of Quantities and Sources . Bethesda, MD: FASEB/LSRO ; 1989 .

Ramsay DJ . Homeostatic control of water balance . In: Arnaud MJ , ed. Hydration Throughout Life . Montrouge: John Libbey Eurotext ; 1998 : 9 – 18 .

Duffey K Popkin BM . Shifts in patterns and consumption of beverages between 1965 and 2002 . Obesity. 2007 ; 15 : 2739 – 2747 .

Morley JE Miller DK Zdodowski C Guitierrez B Perry IIIHM . Fluid intake, hydration and aging . In: Arnaud MJ , ed. Hydration Throughout Life: International Conference Vittel (France) . Montrouge: John Libbey Eurotext ; 1998 : 247 .

Phillips PA Rolls BJ Ledingham JG , et al . Reduced thirst after water deprivation in healthy elderly men . N Engl J Med. 1984 ; 311 : 753 – 759 .

Mack GW Weseman CA Langhans GW Scherzer H Gillen CM Nadel ER . Body fluid balance in dehydrated healthy older men: thirst and renal osmoregulation . J Appl Physiol. 1994 ; 76 : 1615 – 1623 .

Phillips PA Johnston CI Gray L . Disturbed fluid and electrolyte homoeostasis following dehydration in elderly people . Age Ageing. 1993 ; 22 : S26 – S33 .

Phillips PA Bretherton M Johnston CI Gray L . Reduced osmotic thirst in healthy elderly men . Am J Physiol. 1991 ; 261 : R166 – R171 .

Davies I O'Neill PA McLean KA Catania J Bennett D . Age-associated alterations in thirst and arginine vasopressin in response to a water or sodium load . Age Ageing. 1995 ; 24 : 151 – 159 .

Silver AJ Morley JE . Role of the opioid system in the hypodipsia associated with aging . J Am Geriatr Soc. 1992 ; 40 : 556 – 560 .

Sawka MN Latzka WA Matott RP Montain SJ . Hydration effects on temperature regulation . Int J Sports Med. 1998 ; 19 (Suppl 2 ): S108 – S110 .

Sawka MN Cheuvront SN Carter R 3rd . Human water needs . Nutr Rev. 2005 ; 63 (Suppl): S30 – S39 .

Armstrong LE. Heat acclimatization . In: TD Fahey, ed. Encyclopedia of Sports Medicine and Science . Internet Society for Sport Science: http://sportsci.org . 10 March 1998 .

Falk B Dotan R . Children's thermoregulation during exercise in the heat: a revisit . Appl Physiol Nutr Metab. 2008 ; 33 : 420 – 427 .

Bytomski JR Squire DL . Heat illness in children . Curr Sports Med Rep. 2003 ; 2 : 320 – 324 .

Bar-Or O Dotan R Inbar O Rotshtein A Zonder H . Voluntary hypohydration in 10- to 12-year-old boys . J Appl Physiol. 1980 ; 48 : 104 – 108 .

Vogelaere P Pereira C . Thermoregulation and aging . Rev Port Cardiol. 2005 ; 24 : 747 – 761 .

Thompson-Torgerson CS Holowatz LA Kenney WL . Altered mechanisms of thermoregulatory vasoconstriction in aged human skin . Exerc Sport Sci Rev. 2008 ; 36 : 122 – 127 .

Miller PD Krebs RA Neal BJ McIntyre DO . Hypodipsia in geriatric patients . Am J Med. 1982 ; 73 : 354 – 356 .

Albert SG Nakra BR Grossberg GT Caminal ER . Drinking behavior and vasopressin responses to hyperosmolality in Alzheimer's disease . Int Psychogeriatr. 1994 ; 6 : 79 – 86 .

Maughan RJ Shirreffs SM Watson P . Exercise, heat, hydration and the brain . J Am Coll Nutr. 2007 ; 26 (Suppl): S604 – S612 .

Murray B . Hydration and physical performance . J Am Coll Nutr. 2007 ; 26 (Suppl): S542 – S548 .

Sawka MN Noakes TD . Does dehydration impair exercise performance? Med Sci Sports Exerc. 2007 ; 39 : 1209 – 1217 .

Montain SJ Coyle EF . Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise . J Appl Physiol. 1992 ; 73 : 1340 – 1350 .

Cheuvront SN . Carter R, 3rd, Sawka MN. Fluid balance and endurance exercise performance . Curr Sports Med Rep. 2003 ; 2 : 202 – 208 .

Paik IY Jeong MH Jin HE , et al . Fluid replacement following dehydration reduces oxidative stress during recovery . Biochem Biophys Res Commun. 2009 ; 383 : 103 – 107 .

Kovacs MS . A review of fluid and hydration in competitive tennis . Int J Sports Physiol Perform. 2008 ; 3 : 413 – 423 .

Cheuvront SN Montain SJ Sawka MN . Fluid replacement and performance during the marathon . Sports Med. 2007 ; 37 : 353 – 357 .

Cheuvront SN . Carter R, 3rd, Haymes EM, Sawka MN. No effect of moderate hypohydration or hyperthermia on anaerobic exercise performance . Med Sci Sports Exerc. 2006 ; 38 : 1093 – 1097 .

Penkman MA Field CJ Sellar CM Harber VJ Bell GJ . Effect of hydration status on high-intensity rowing performance and immune function . Int J Sports Physiol Perform. 2008 ; 3 : 531 – 546 .

Bergeron MF McKeag DB Casa DJ , et al . Youth football: heat stress and injury risk . Med Sci Sports Exerc. 2005 ; 37 : 1421 – 1430 .

Godek SF Godek JJ Bartolozzi AR . Hydration status in college football players during consecutive days of twice-a-day preseason practices . Am J Sports Med. 2005 ; 33 : 843 – 851 .

Cheuvront SN Carter R 3rd Castellani JW Sawka MN . Hypohydration impairs endurance exercise performance in temperate but not cold air . J Appl Physiol. 2005 ; 99 : 1972 – 1976 .

Kenefick RW Mahood NV Hazzard MP Quinn TJ Castellani JW . Hypohydration effects on thermoregulation during moderate exercise in the cold . Eur J Appl Physiol. 2004 ; 92 : 565 – 570 .

Maughan RJ Watson P Shirreffs SM . Heat and cold: what does the environment do to the marathon runner? Sports Med. 2007 ; 37 : 396 – 399 .

American Academy of Pediatrics . Climatic heat stress and the exercising child and adolescent. American Academy of Pediatrics. Committee on Sports Medicine and Fitness . Pediatrics. 2000 ; 106 : 158 – 159 .

Cian C Barraud PA Melin B Raphel C . Effects of fluid ingestion on cognitive function after heat stress or exercise-induced dehydration . Int J Psychophysiol. 2001 ; 42 : 243 – 251 .

Cian C Koulmann PA Barraud PA Raphel C Jimenez C Melin B . Influence of variations of body hydration on cognitive performance . J Psychophysiol. 2000 ; 14 : 29 – 36 .

Gopinathan PM Pichan G Sharma VM . Role of dehydration in heat stress-induced variations in mental performance . Arch Environ Health. 1988 ; 43 : 15 – 17 .

D'Anci KE Vibhakar A Kanter JH Mahoney CR Taylor HA . Voluntary dehydration and cognitive performance in trained college athletes . Percept Mot Skills. 2009 ; 109 : 251 – 269 .

Suhr JA Hall J Patterson SM Niinisto RT . The relation of hydration status to cognitive performance in healthy older adults . Int J Psychophysiol. 2004 ; 53 : 121 – 125 .

Szinnai G Schachinger H Arnaud MJ Linder L Keller U . Effect of water deprivation on cognitive-motor performance in healthy men and women . Am J Physiol Regul Integr Comp Physiol. 2005 ; 289 : R275 – R280 .

Neave N Scholey AB Emmett JR Moss M Kennedy DO Wesnes KA . Water ingestion improves subjective alertness, but has no effect on cognitive performance in dehydrated healthy young volunteers . Appetite. 2001 ; 37 : 255 – 256 .

Rogers PJ Kainth A Smit HJ . A drink of water can improve or impair mental performance depending on small differences in thirst . Appetite. 2001 ; 36 : 57 – 58 .

Edmonds CJ Jeffes B . Does having a drink help you think? 6–7-year-old children show improvements in cognitive performance from baseline to test after having a drink of water . Appetite. 2009 ; 53 : 469 – 472 .

Edmonds CJ Burford D . Should children drink more water?: the effects of drinking water on cognition in children . Appetite. 2009 ; 52 : 776 – 779 .

Benton D Burgess N . The effect of the consumption of water on the memory and attention of children . Appetite. 2009 ; 53 : 143 – 146 .

Cohen S . After effects of stress on human performance during a heat acclimatization regimen . Aviat Space Environ. Med. 1983 ; 54 : 709 – 713 .

Culp KR Wakefield B Dyck MJ Cacchione PZ DeCrane S Decker S . Bioelectrical impedance analysis and other hydration parameters as risk factors for delirium in rural nursing home residents . J Gerontol A Biol Sci Med Sci. 2004 ; 59 : 813 – 817 .

Lawlor PG . Delirium and dehydration: some fluid for thought? Support Care Cancer. 2002 ; 10 : 445 – 454 .

Voyer P Richard S Doucet L Carmichael PH . Predisposing factors associated with delirium among demented long-term care residents . Clin Nurs Res. 2009 ; 18 : 153 – 171 .

Leiper JB . Intestinal water absorption – implications for the formulation of rehydration solutions . Int J Sports Med. 1998 ; 19 (Suppl 2 ): S129 – S132 .

Ritz P Berrut G . The importance of good hydration for day-to-day health . Nutr Rev. 2005 ; 63 : S6 – S13 .

Arnaud MJ . Mild dehydration: a risk factor of constipation? Eur J Clin Nutr. 2003 ; 57 (Suppl): S88 – S95 .

Young RJ Beerman LE Vanderhoof JA . Increasing oral fluids in chronic constipation in children . Gastroenterol Nurs. 1998 ; 21 : 156 – 161 .

Murakami K Sasaki S Okubo H , et al . Association between dietary fiber, water and magnesium intake and functional constipation among young Japanese women . Eur J Clin Nutr. 2007 ; 61 : 616 – 622 .

Lindeman RD Romero LJ Liang HC Baumgartner RN Koehler KM Garry PJ . Do elderly persons need to be encouraged to drink more fluids? J Gerontol A Biol Sci Med Sci. 2000 ; 55 : M361 – M365 .

Robson KM Kiely DK Lembo T . Development of constipation in nursing home residents . Dis Colon Rectum. 2000 ; 43 : 940 – 943 .

Cuomo R Grasso R Sarnelli G , et al . Effects of carbonated water on functional dyspepsia and constipation . Eur J Gastroenterol Hepatol. 2002 ; 14 : 991 – 999 .

Kosek M Bern C Guerrant RL . The global burden of diarrhoeal disease, as estimated from studies published between 1992 and 2000 . Bull World Health Organ. 2003 ; 81 : 197 – 204 .

Atia AN Buchman AL . Oral rehydration solutions in non-cholera diarrhea: a review . Am J Gastroenterol. 2009 ; 104 : 2596 – 2604 , quiz 2605.

Schoen EJ . Minimum urine total solute concentration in response to water loading in normal men . J Appl Physiol. 1957 ; 10 : 267 – 270 .

Sporn IN Lancestremere RG Papper S . Differential diagnosis of oliguria in aged patients . N Engl J Med. 1962 ; 267 : 130 – 132 .

Brenner BM , ed. Brenner and Rector's The Kidney , 8th edn. Philadelphia, PA: Saunders Elsevier ; 2007 .

Lindeman RD Van Buren HC Raisz LG . Osmolar renal concentrating ability in healthy young men and hospitalized patients without renal disease . N Engl J Med. 1960 ; 262 : 1306 – 1309 .

Shirreffs SM Maughan RJ . Control of blood volume: long term and short term regulation . In: Arnaud MJ , ed. Hydration Throughout Life . Montrouge: John Libbey Eurotext ; 1998 : 31 – 39 .

Schroeder C Bush VE Norcliffe LJ , et al . Water drinking acutely improves orthostatic tolerance in healthy subjects . Circulation. 2002 ; 106 : 2806 – 2811 .

Lu CC Diedrich A Tung CS , et al . Water ingestion as prophylaxis against syncope . Circulation. 2003 ; 108 : 2660 – 2665 .

Callegaro CC Moraes RS Negrao CE , et al . Acute water ingestion increases arterial blood pressure in hypertensive and normotensive subjects . J Hum Hypertens. 2007 ; 21 : 564 – 570 .

Ando SI Kawamura N Matsumoto M , et al . Simple standing test predicts and water ingestion prevents vasovagal reaction in the high-risk blood donors . Transfusion. 2009 ; 49 : 1630 – 1636 .

Brick JE Lowther CM Deglin SM . Cold water syncope . South Med J. 1978 ; 71 : 1579 – 1580 .

Farb A Valenti SA . Swallow syncope . Md Med J. 1999 ; 48 : 151 – 154 .

Casella F Diana A Bulgheroni M , et al . When water hurts . Pacing Clin Electrophysiol. 2009 ; 32 : e25 – e27 .

Shirreffs SM Merson SJ Fraser SM Archer DT . The effects of fluid restriction on hydration status and subjective feelings in man . Br J Nutr. 2004 ; 91 : 951 – 958 .

Blau J . Water deprivation: a new migraine precipitant . Headache. 2005 ; 45 : 757 – 759 .

Blau JN Kell CA Sperling JM . Water-deprivation headache: a new headache with two variants . Headache. 2004 ; 44 : 79 – 83 .

Spigt MG Kuijper EC Schayck CP , et al . Increasing the daily water intake for the prophylactic treatment of headache: a pilot trial . Eur J Neurol. 2005 ; 12 : 715 – 718 .

Valtin H . “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 x 8”? Am J Physiol Regul Integr Comp Physiol. 2002 ; 283 : R993 – 1004 .

Negoianu D Goldfarb S . Just add water . J Am Soc Nephrol. 2008 ; 19 : 1041 – 1043 .

Madison KC . Barrier function of the skin: “la raison d'etre” of the epidermis . J Invest Dermatol. 2003 ; 121 : 231 – 241 .

Champion RH Burton JL Ebling FJG , eds. Textbook of Dermatology (Rook) . Oxford: Blackwell ; 1992 .

Vivanti A Harvey K Ash S Battistutta D . Clinical assessment of dehydration in older people admitted to hospital: what are the strongest indicators? Arch Gerontol Geriatr. 2008 ; 47 : 340 – 355 .

Colletti JE Brown KM Sharieff GQ Barata IA Ishimine P Committee APEM . The management of children with gastroenteritis and dehydration in the emergency department . J Emerg Med. 2009 .

Williams S Krueger N Davids M Kraus D Kerscher M . Effect of fluid intake on skin physiology: distinct differences between drinking mineral water and tap water . Int J Cosmet Sci. 2007 ; 29 : 131 – 138 .

Mac-Mary S Creidi P Marsaut D , et al . Assessment of effects of an additional dietary natural mineral water uptake on skin hydration in healthy subjects by dynamic barrier function measurements and clinic scoring . Skin Res Technol. 2006 ; 12 : 199 – 205 .

Warner RR Stone KJ Boissy YL . Hydration disrupts human stratum corneum ultrastructure . J Invest Dermatol. 2003 ; 120 : 275 – 284 .

Loden M . Role of topical emollients and moisturizers in the treatment of dry skin barrier disorders . Am J Clin Dermatol. 2003 ; 4 : 771 – 788 .

Manz F Wentz A . The importance of good hydration for the prevention of chronic diseases . Nutr Rev. 2005 ; 63 (Suppl): S2 – S5 .

Panel on Dietetic Products Nutrition and Allergies . Dietary reference values for water Scientific Opinion of the Panel on Dietetic Products, Nutrition and Allergies (Question No EFSA-Q-2005-015a) . EFSA J. 2009 ; 8 ( 3 ): 1459 .

Stookey JD Constant F Gardner C Popkin B . Replacing sweetened caloric beverages with drinking water is associated with lower energy intake . Obesity. 2007 ; 15 : 3013 – 3022 .

Stookey JD Constant F Gardner C Popkin BM . Drinking water is associated with weight loss . Obesity. 2008 ; 16 : 2481 – 2488 .

Turrini A Saba A Perrone D Cialfa E D'Amicis D . Food consumption patterns in Italy: the INN-CA Study 1994–1996 . Eur J Clin Nutr. 2001 ; 55 : 571 – 588 .

Sichert-Hellert W Kersting M Manz F . Fifteen year trends in water intake in German children and adolescents: results of the DONALD Study. Dortmund Nutritional and Anthropometric Longitudinally Designed Study . Acta Paediatr. 2001 ; 90 : 732 – 737 .

Raman A Schoeller DA Subar AF , et al . Water turnover in 458 American adults 40–79 yr of age . Am J Physiol Renal Physiol. 2004 ; 286 : F394 – F401 .

Daniels MC Popkin BM . The impact of water intake on energy intake and weight status: a review . Nutr Rev. 2010 ; 9 :in press.

Piernas C Popkin B . Snacking trends in U.S. adults between 1977 and 2006 . J Nutr . 2010 ; 140 : 325 – 332 .

Piernas C Popkin BM . Trends in snacking among U.S. children . Health Affairs. 2010 ; 29 : 398 – 404 .

Popkin BM Duffey KJ. Does hunger and satiety drive eating anymore? Increasing eating occasions and decreasing time between eating occasions in the United States . Am J Clin Nutr . 2010 ; 91 : 1342 – 1347 .

Muckelbauer R Libuda L Clausen K Toschke AM Reinehr T Kersting M . Promotion and provision of drinking water in schools for overweight prevention: randomized, controlled cluster trial . Pediatrics. 2009 ; 123 : e661 – e667 .

Bar-or O . Temperature regulation during exercise in children and aolescents . In: Gisolfi C Lamb DR , eds. Youth, Exercise, and Sport: Symposium: Papers and Discussions . Indianapolis: Benchmark ; 1989 : 335 – 367 .

National Research Council . Recommended Dietary Allowances . Washington, DC: National Academy Press ; 1989 .

Prentice A Branca F Decsi T , et al . Energy and nutrient dietary reference values for children in Europe: methodological approaches and current nutritional recommendations . Br J Nutr. 2004 ; 92 (Suppl 2 ): S83 – 146 .

German Nutrition Society, Austrian Nutrition Society, Swiss Society for Nutrition Research Swiss Nutrition Association . Reference Values for Nutrient Intake (in English) , 1st edn. Frankfurt: Umschau Brau ; 2002 .

Stookey JD Pieper CF Cohen HJ . Is the prevalence of dehydration among community-dwelling older adults really low? Informing current debate over the fluid recommendation for adults aged 70+years . Public Health Nutr. 2005 ; 8 : 1275 – 1285 .

Malik VS Popkin BM Bray G Després J-P Hu FB. Sugar sweetened beverages, obesity, type 2 diabetes and cardiovascular disease risk . Circulation 2010 ; 121 : 1356 – 1364 .

Teff KL Grudziak J Townsend RR , et al . Endocrine and metabolic effects of consuming fructose- and glucose-sweetened beverages with meals in obese men and women: influence of insulin resistance on plasma triglyceride responses . J Clin Endocrinol Metab. 2009 ; 94 : 1562 – 1569 .

Stanhope KL . Consuming fructose-sweetened, not glucose-sweetened, beverages increases visceral adiposity and lipids and decreases insulin sensitivity in overweight/obese humans . J Clin Investigat. 2009 ; 119 : 1322 – 1334 .

Stanhope KL Havel PJ . Endocrine and metabolic effects of consuming beverages sweetened with fructose, glucose, sucrose, or high-fructose corn syrup . Am J Clin Nutr. 2008 ; 88 (Suppl): S1733 – S1737 .

Stanhope KL Griffen SC Bair BR Swarbrick MM Keim NL Havel PJ . Twenty-four-hour endocrine and metabolic profiles following consumption of high-fructose corn syrup-, sucrose-, fructose-, and glucose-sweetened beverages with meals . Am J Clin Nutr. 2008 ; 87 : 1194 – 1203 .

Altman P . Blood and Other Body Fluids . Washington, DC: Federation of American Societies for Experimental Biology ; 1961 .

Kalhoff H . Mild dehydration: a risk factor of broncho-pulmonary disorders? Eur J Clin Nutr. 2003 ; 57 (Suppl 2 ): S81 – S87 .

Taitz LS Byers HD . High calorie-osmolar feeding and hypertonic dehydration . Arch Dis Child. 1972 ; 47 : 257 – 260 .

Burge MR Garcia N Qualls CR Schade DS . Differential effects of fasting and dehydration in the pathogenesis of diabetic ketoacidosis . Metabolism. 2001 ; 50 : 171 – 177 .

Jayashree M Singhi S . Diabetic ketoacidosis: predictors of outcome in a pediatric intensive care unit of a developing country . Pediatr Crit Care Med. 2004 ; 5 : 427 – 433 .

Hebert LA Greene T Levey A Falkenhain ME Klahr S . High urine volume and low urine osmolality are risk factors for faster progression of renal disease . Am J Kidney Dis. 2003 ; 41 : 962 – 971 .

Bankir L Bardoux P Mayaudon H Dupuy O Bauduceau B . [Impaired urinary flow rate during the day: a new factor possibly involved in hypertension and in the lack of nocturnal dipping] . Arch Mal Coeur Vaiss. 2002 ; 95 : 751 – 754 .

Blanker MH Bernsen RM Ruud Bosch JL , et al . Normal values and determinants of circadian urine production in older men: a population based study . J Urol. 2002 ; 168 : 1453 – 1457 .

Chan J Knutsen SF Blix GG Lee JW Fraser GE . Water, other fluids, and fatal coronary heart disease: the Adventist Health Study . Am J Epidemiol. 2002 ; 155 : 827 – 833 .

Kelly J Hunt BJ Lewis RR , et al . Dehydration and venous thromboembolism after acute stroke . QJM. 2004 ; 97 : 293 – 296 .

Bhalla A Sankaralingam S Dundas R Swaminathan R Wolfe CD Rudd AG . Influence of raised plasma osmolality on clinical outcome after acute stroke . Stroke. 2000 ; 31 : 2043 – 2048 .

Longo-Mbenza B Phanzu-Mbete LB M'Buyamba-Kabangu JR , et al . Hematocrit and stroke in black Africans under tropical climate and meteorological influence . Ann Med Interne (Paris). 1999 ; 150 : 171 – 177 .

Diamond PT Gale SD Evans BA . Relationship of initial hematocrit level to discharge destination and resource utilization after ischemic stroke: a pilot study . Arch Phys Med Rehabil. 2003 ; 84 : 964 – 967 .

Mazzola BL von Vigier RO Marchand S Tonz M Bianchetti MG . Behavioral and functional abnormalities linked with recurrent urinary tract infections in girls . J Nephrol. 2003 ; 16 : 133 – 138 .

Wilde MH Carrigan MJ . A chart audit of factors related to urine flow and urinary tract infection . J Adv Nurs. 2003 ; 43 : 254 – 262 .

Altieri A La Vecchia C Negri E . Fluid intake and risk of bladder and other cancers . Eur J Clin Nutr. 2003 ; 57 (Suppl 2 ): S59 – S68 .

Donat SM Bayuga S Herr HW Berwick M . Fluid intake and the risk of tumor recurrence in patients with superficial bladder cancer . J Urol. 2003 ; 170 : 1777 – 1780 .

Radosavljevic V Jankovic S Marinkovic J Djokic M . Fluid intake and bladder cancer. A case control study . Neoplasma. 2003 ; 50 : 234 – 238 .

Math MV Rampal PM Faure XR Delmont JP . Gallbladder emptying after drinking water and its possible role in prevention of gallstone formation . Singapore Med J. 1986 ; 27 : 531 – 532 .

Aufderheide S Lax D Goldberg SJ . Gender differences in dehydration-induced mitral valve prolapse . Am Heart J. 1995 ; 129 : 83 – 86 .

Martin B Harris A Hammel T Malinovsky V . Mechanism of exercise-induced ocular hypotension . Invest Ophthalmol Vis Sci. 1999 ; 40 : 1011 – 1015 .

Brucculeri M Hammel T Harris A Malinovsky V Martin B . Regulation of intraocular pressure after water drinking . J Glaucoma. 1999 ; 8 : 111 – 116 .

• dehydration
• energy intake
• water drinking
• fluid intake
• water requirements

Email alerts

Citing articles via.

• Recommend to your Library

Affiliations

• Online ISSN 1753-4887
• Print ISSN 0029-6643
• Copyright © 2024 International Life Sciences Institute
• About Oxford Academic
• Publish journals with us
• University press partners
• What we publish
• New features  
• Open access
• Institutional account management
• Rights and permissions
• Get help with access
• Accessibility
• Advertising
• Media enquiries
• Oxford University Press
• Oxford Languages
• University of Oxford

Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide

• Copyright © 2024 Oxford University Press
• Cookie settings
• Cookie policy
• Privacy policy
• Legal notice

This Feature Is Available To Subscribers Only

Sign In or Create an Account

This PDF is available to Subscribers Only

For full access to this pdf, sign in to an existing account, or purchase an annual subscription.

Drinking Water Source and Intake Are Associated with Distinct Gut Microbiota Signatures in US and UK Populations

Affiliations.

• 1 Danone Research, Palaiseau, France.
• 2 IT&M Innovation.
• PMID: 34642755
• PMCID: PMC8754568
• DOI: 10.1093/jn/nxab312

Background: The microbiome of the digestive tract exerts fundamental roles in host physiology. Extrinsic factors including lifestyle and diet are widely recognized as key drivers of gut and oral microbiome compositions. Although drinking water is among the food items consumed in the largest amount, little is known about its potential impact on the microbiome.

Objectives: We explored the associations of plain drinking water source and intake with gut and oral microbiota compositions in a population-based cohort.

Methods: Microbiota, health, lifestyle, and food intake data were extracted from the American Gut Project public database. Associations of drinking water source (bottled, tap, filtered, or well water) and intake with global microbiota composition were evaluated using linear and logistic models adjusted for anthropometric, diet, and lifestyle factors in 3413 and 3794 individuals, respectively (fecal samples; 56% female, median [IQR] age: 48 [36-59] y; median [IQR] BMI: 23.3 [20.9-26.3] kg/m2), and in 283 and 309 individuals, respectively (oral samples).

Results: Drinking water source ranked among the key contributing factors explaining the gut microbiota variation, accounting for 13% [Faith's phylogenetic diversity (Faith's PD)] and 47% (Bray-Curtis dissimilarity) of the age effect size. Drinking water source was associated with differences in gut microbiota signatures, as revealed by β diversity analyses (P < 0.05; Bray-Curtis dissimilarity, weighted UniFrac distance). Subjects drinking mostly well water had higher fecal α diversity (P < 0.05; Faith's PD, observed amplicon sequence variants), higher Dorea, and lower Bacteroides, Odoribacter, and Streptococcus than the other groups. Low water drinkers also exhibited gut microbiota differences compared with high water drinkers (P < 0.05; Bray-Curtis dissimilarity, unweighted UniFrac distance) and a higher abundance of Campylobacter. No associations were found between oral microbiota composition and drinking water consumption.

Conclusions: Our results indicate that drinking water may be an important factor in shaping the human gut microbiome and that integrating drinking water source and intake as covariates in future microbiome analyses is warranted.

Keywords: American Gut Project; drinking water; gut microbiota diversity; human microbiome; oral microbiota; water intake; water source.

© The Author(s) 2021. Published by Oxford University Press on behalf of the American Society for Nutrition.

• Drinking Water*
• Gastrointestinal Microbiome*
• Middle Aged
• RNA, Ribosomal, 16S
• United Kingdom
• Drinking Water

• Table of Contents

Volume 10 — April 11, 2013

Article Tools

• PDF - 258 KB
• Download citation
• Este resumen en español
• Send feedback to PCD
• Display this article on your Web site

ORIGINAL RESEARCH

Behaviors and attitudes associated with low drinking water intake among us adults, food attitudes and behaviors survey, 2007, navigate this article, introduction, author information, alyson b. goodman, md, mph; heidi m. blanck, phd; bettylou sherry, phd, rd; sohyun park, phd; linda nebeling, phd, mph, rd; amy l. yaroch, phd.

Suggested citation for this article: Goodman AB, Blanck HM, Sherry B, Park S, Nebeling L, Yaroch AL. Behaviors and Attitudes Associated With Low Drinking Water Intake Among US Adults, Food Attitudes and Behaviors Survey, 2007. Prev Chronic Dis 2013;10:120248. DOI: http://dx.doi.org/10.5888/pcd10.120248 .

PEER REVIEWED

Introduction Water is vital for life, and plain water is a calorie-free option for hydration. Increasing consumption of drinking water is a strategy to reduce energy intake and lose or maintain weight; however, information on the characteristics of consumers who drink water is limited. Our objective was to describe the characteristics of people who have a low intake of drinking water and to determine associations between their behaviors and attitudes and their intake of water.

Methods We analyzed data from a nationally representative sample of 3,397 US adults who participated in the National Cancer Institute’s 2007 Food Attitudes and Behaviors Survey. Multivariable logistic regression was used to identify sociodemographic characteristics and health-related behaviors and attitudes associated with self-reported drinking water intake of less than 4 cups per day.

Results Overall, 7% of adults reported no daily consumption of drinking water, 36% reported drinking 1 to 3 cups, 35% reported drinking 4 to 7 cups, and 22% reported drinking 8 cups or more. The likelihood of drinking less than 4 cups of water daily was significantly higher among participants aged 55 years or older than among those aged 18 to 34 (adjusted odds ratio [AOR], 1.3), among residents of the Northeast than among residents of the South (AOR, 1.4), among participants who consumed 1 cup or less of fruits or vegetables per day than among those who consumed 4.5 cups or more (AOR, 3.0), among participants who did not exercise than among those who exercised 150 minutes or more per week (AOR, 1.7), and among participants who were neither trying to gain nor lose weight than among those trying to lose weight (AOR, 1.3).

Conclusion Low drinking water intake was associated with age, region of residence, and several unhealthful behaviors and attitudes. Understanding characteristics associated with low drinking water intake may help to identify populations that could benefit from interventions to help adults drink more water.

Top of Page

Adequate water intake has health benefits and is essential for preventing dehydration; dehydration is associated with adverse health effects such as headache, urolithiasis, and impaired cognition (1). Health risks (eg, dental caries, obesity) associated with intake of high levels of calorically sweetened beverages (eg, regular soda, fruit drinks, sports drinks) decrease when plain drinking water is substituted for these beverages (1,2). Water consumption before meals and the replacement of calorically sweetened beverages with water are associated with lower energy intake, and increased plain water intake among adults is associated with significant weight maintenance or loss (3–9). The Dietary Guidelines for Americans 2010 encourages adults to drink water as a healthful means of hydration, and public health organizations and others are bringing this message to communities (10–13).

According to 2005–2008 National Health and Nutrition Examination Survey (NHANES) data, mean plain water intake among US adults (aged ≥20 years) was 4.4 cups for men and 4.3 cups for women (14). Little research has been conducted on the association of individual water consumption practices with diet and meal patterns (15). Although water intake has been associated with individual factors (eg, physical activity, age), little is known about how water intake is related to other food- and health-related behaviors and attitudes (14–17). A comprehensive understanding of how these factors are related to water intake may help identify populations and associated attitudes and behaviors amenable to intervention. For example, clinical or public health messages about water intake could be bundled with messages about associated health behaviors. The purposes of our study were to use a data set with varied information on behaviors and attitudes to quantify daily drinking water intake, to identify sociodemographic and health characteristics associated with low water intake, and to describe the association of food- and health-related behaviors and attitudes with low drinking water intake.

We used data for this cross-sectional study from the National Cancer Institute’s Food Attitudes and Behaviors (FAB) Survey, a mail-panel survey of US adults conducted from October through December 2007. The FAB Survey was approved by the National Cancer Institute’s institutional review board (18).

Participants/recruitment

FAB participants were US residents aged 18 years or older recruited via quota sampling of households in Synovate’s Consumer Opinion Panel (N = 450,000) in the fall of 2006. The FAB survey was first mailed to a stratified random sample of 5,803 adults; 200 additional surveys were mailed later (sample balanced to reflect the US population by region of residence, annual household income, population density, age, and household size); African Americans were oversampled (unweighted response rate, 28%). In total, 3,418 of 6,003 questionnaires were returned (response rate, 57%). For our study, we excluded 167 questionnaires (21 overall incomplete, 23 missing the outcome variable, and 123 missing sociodemographic data), leaving a final study sample of 3,251 respondents. Drinking water intake did not significantly differ between included and excluded respondents. The percentage of respondents with unknown values or missing data for individual exposure variables ranged from less than 0.1% to 7.0%; we excluded respondents with data missing for a given variable from analyses involving that variable.

Daily water intake was determined on the basis of participants’ responses to the question, “On average, how many cups of bottled or tap water do you drink each day?” Response options were “none,” “1-3 cups,” “4-7 cups,” and “8 or more cups.” For multivariable logistic regression models, we dichotomized water intake as “less than 4” or “4 or more cups” per day based on the mean water intake (approximately 4.3 cups) among US adults according to 2005–2008 NHANES data (14,15).

Sociodemographic variables were age (18–34 years, 35–54 years, or ≥55 years), sex, race/ethnicity (non-Hispanic white, non-Hispanic black, or other [including Hispanic, non-Hispanic Asian, American Indian, Native Hawaiian, and mixed race]), region of residence (Northeast, Midwest, South, or West), education level (less than a high school diploma, high school degree, some college, or college degree), and annual household income (<$20,000; $20,000-$44,999; $45,000-$74,999; or ≥$75,000).

Variables describing health- and eating-related characteristics for our primary multivariable model were chosen on the basis of likely or known associations with health status and thought to be associated with water intake: weight status based on body mass index (BMI), calculated from self-reported height and weight (underweight/normal weight [BMI <25.0 kg/m 2 ], overweight [BMI 25.0 to <30 kg/m 2 ], obese [BMI ≥30 kg/m 2 ]) (19); daily fruit and vegetable intake (from a validated 16-item screener [18]), categorized as ≤1, >1 to <4.5, or ≥4.5 cups based on recommendations for a 2,000 kilocalorie diet (11); minutes of moderate physical activity per week (0, 1 to <150, ≥150) based on the US Physical Activity Guidelines for adults to get at least 150 minutes of moderate-intensity exercise per week (20); cigarette smoking status (never, former, current); intentions for weight management (neither trying to lose nor gain weight, trying to gain weight, trying to lose weight); hours of television watched on an average day (≤2, >2 to <4, ≥4); and number of hours of sleep on an average night (<6, 6 to <8, ≥8).

We conducted secondary analyses to determine whether the following variables with hypothesized associations with health were related to drinking water intake (while maintaining the parsimony of our multivariate model): how often fruits and vegetables were eaten while growing up (rarely, more than once per week, once daily, more than once daily), whether the primary grocery shopper shops at farmers markets or cooperatives (yes, no), meals eaten per week while watching television (none, 1–4, ≥5 meals), fast food intake (none, once/week, more than once/week), meals per week eaten at the table with family or friends (none, 1–4, ≥5), cups of daily 100% juice intake (none, 1, ≥2 cups), and respondents’ attitudes about “how often worrying about your health has led you to change the way you ate in the past year” (not at all/a little, somewhat, quite a bit/a lot). Variables based on respondents’ agreement with the following: “What I eat doesn’t really affect my health,” “I don’t eat fruits and vegetables as much as I like to because they cost too much,” “It’s hard for me to purchase fruits and vegetables in my neighborhood,” and “I think meals should include some meat” (disagree, neither disagree nor agree, agree).

Statistical analyses

Data on sex, race/ethnicity, age, education, and annual household income were weighted using 2000 US Census data to create a sample distribution similar to the national distribution. Chi-square tests were used to evaluate the frequency of drinking water intake by exposure variables; significance was set at P  < .05. Odds ratios (OR) and 95% confidence intervals (CIs) for variables associated with low water intake (<4 cups daily) were calculated from multivariable logistic regression models. The model we used in our primary analysis consisted of sociodemographic variables and selected health- and eating-related variables. In our secondary analyses, we created separate logistic regression models for each exposure variable that were adjusted for age, sex, race/ethnicity, region of residence, income, and education. All analyses were conducted using SAS version 9.2 (SAS Institute, Inc, Cary, North Carolina).

Of the 3,251 respondents, 43.7% drank less than 4 cups of water per day ( Table 1 ). Approximately 7% reported consuming no drinking water daily, 36% drank 1 to 3 cups, 35% drank 4 to 7 cups, and 22% drank 8 cups or more. On the basis of χ 2 tests, daily drinking water intake (<4 vs ≥4 cups) varied significantly by age, race/ethnicity, education level, annual household income, weight status, moderate physical activity, fruit and vegetable intake, smoking status, intentions for weight management, and hours of television watched daily.

Multivariable logistic regression indicated that the likelihood of low drinking water intake (<4 cups/d) was significantly higher among people aged 55 or older (vs aged 18–34), living in the Northeast (vs South), trying to gain weight (vs trying to lose weight), participating in no moderate physical activity and 1 to fewer than 150 minutes per week (vs ≥150 minutes/week), and eating less than 4.5 cups of fruits and vegetables daily (vs ≥4.5 cups/d) (Table 1). Lower odds of drinking less than 4 cups of water per day were observed among respondents of “other” race/ethnicity than among whites and among former smokers than among never smokers.

Results of secondary analyses indicated that drinking water intake differed significantly across many eating-related behaviors (χ 2 test, P < .05) ( Table 2 ). Adjusted ORs indicate that variables significantly related to greater odds for low drinking water intake were recalling eating fruits once daily or less often while growing up (vs more than once daily), recalling eating vegetables once daily or less often while growing up (vs more than once daily), eating fast food more than once per week (vs none), and eating fewer than 5 dinners per week around a table with family or friends (vs ≥5 dinners/week). Shopping at farmers markets or cooperatives (vs not) and intake of 1 or more cups per day of 100% juice (vs none) were significantly related to lower odds for low drinking water intake (Table 2).

Greater odds of low drinking water intake were significantly related to various attitudes/beliefs about food and health ( Table 3 ). Factors associated with higher odds for low drinking water intake included replying to survey questions as follows: “agree” or “neither disagree nor agree” that “what I eat doesn’t really affect my health” (vs “disagree”); “not at all/a little” or “somewhat” to “How often has worrying about your health led you to change what you ate in the past year?” (vs “quite a bit/a lot”); “agree” or “neither disagree nor agree” that “I don’t eat fruits and vegetables as much as I like to because they cost too much” (vs “disagree”); “agree” that “It’s hard for me to purchase fruits and vegetables in my neighborhood” (vs “disagree”); and “agree” that “I think meals should include some meat” (vs “disagree”).

Our findings indicated that nearly half of respondents drank less than 4 cups per day of water (ie, bottled or tap water) and that 56% of respondents reported drinking 4 or more cups of water daily. These results are consistent with those based on 2005–2008 NHANES data, which indicated that US adults consumed an average of 4.3 cups of water per day (14,15). The biologic requirement for water may be met with plain water or via foods and other beverages. Results from previous epidemiologic studies indicate that water intake may be inversely related to volume of calorically sweetened beverages and other fluid intake (4).

Our results indicated that low drinking water intake was associated with many demographic characteristics, including older age. Despite being susceptible to dehydration due to increased prevalence of chronic diseases and the use of multiple medications, older adults have lower fluid consumption primarily due to a decrease in thirst (1,21). Previous studies indicate that water consumption decreases with age; a study of 4,112 US adults by Kant et al found lower plain water intake among older US adults (15,21,22). Kant et al reported no significant differences in water intake by race/ethnicity (15), whereas we found significantly higher intake among respondents in the “other” race/ethnicity category than among whites. The reasons for this association are unclear (FAB was not powered to detect differences among subgroups in this diverse category). In a study of 4,292 Florida students in grades 6 through 8, Park et al found significantly lower odds of low drinking water intake among Hispanic/Latino or “other”/non-Hispanic adolescents than among white adolescents (adjusted OR = 0.79 and OR = 0.76, respectively), results that are similar to those we obtained among adults (23). Although our study found no association between drinking water intake and education or household income in multivariable models, previous studies reported that plain water intake is positively associated with years of education but not associated with poverty-income ratio (15). An analysis of the US Department of Agriculture Nationwide Food Consumption Survey of 1977 found lower tap water intake in the Northeast (1.2 L/d) than in other regions (1.4 L/d), possibly due to greater need for water among residents in regions with warm or humid climates (24).

Our findings of associations between water intake and certain behaviors were similar to those found in previous research. Meeting the national recommendation for 150 minutes per week of moderate physical activity was associated with significantly higher drinking water intake in this and a previous study (15), which is not surprising given that physical activity leads to increased hydration needs due to sweating (1). The results of our multivariable regression analysis showed no association between water intake and time spent watching television, which is consistent with results of a study among 3,867 US children and adolescents (25). Our finding that former smokers were likely to drink more water than those who never smoked might be explained by the common practice of encouraging participants in tobacco cessation programs to increase their water intake (26).

Low fruit and vegetable intake, which epidemiologic studies link to higher risk of chronic disease (11), was associated with drinking significantly less water in multivariable regression models. In addition, in models controlled for sociodemographic variables, respondents with unhealthful eating behaviors and attitudes (eg, high fast-food intake) drank significantly less water, whereas healthful eating behaviors and attitudes (eg, shopping at farmers markets) were related to drinking more water. These results, which are consistent with findings from previous epidemiologic studies (14–17), add to a growing body of evidence that drinking water intake is associated with healthful dietary practices and attitudes. Whether drinking water supports these healthful dietary patterns or simply coexists with them is unclear. Nonetheless, this evidence suggests that health educators or health care practitioners aiming to promote increased water intake should keep in mind that low water consumption may be closely tied to other unhealthful behaviors.

In our study, respondents trying to lose weight consumed significantly more water than those trying to gain weight; however, results of a previous study (15) showed no significant difference in water intake among respondents trying to lose weight in the previous year than among those not trying to lose weight. Although there is a known significant negative association between energy intake and water consumption, evidence is less clear about the relationship between BMI and water intake. In our study, BMI and water intake levels were unrelated after models controlled for sociodemographics and health-related variables. There are at least 3 plausible explanations for this lack of association: 1) the self-reported BMI values of survey participants may be lower than the true values because survey respondents underestimated weight and overestimated height (27,28), thus decreasing our ability to detect an association; 2) the cross-sectional data did not allow us to assess whether prior behaviors of survey participants may have contributed to weight gain; and 3) our adjustments for factors closely associated with obesity, such as physical activity level or fruit and vegetable intake, may have masked the bivariate association we found between water intake and BMI.

Study limitations

FAB data are cross-sectional and the survey results can show only an association between factors, not a causal relationship. The FAB sample was selected from a consumer opinions panel rather than the US population (due to declining response to random–digit-dial telephone surveys); this method is commonly used in other nutrition and health studies such as Styles (18). The response rate of 57% is similar to other random–digit-dial and consumer opinion mailed surveys; information on nonresponders was not available. To minimize bias, households from the larger consumer opinions panel pool selected for FAB were similar to the US population (by age, household income, geographic region, population density, and household size), and data were weighted using US Census estimates; however, these efforts do not guarantee lack of residual bias due to sample selection or nonresponse (18). FAB oversampled African Americans as part of the study design, but the sample size for “other” racial/ethnic groups was not sufficient for subgroup analyses. Dietary intake estimates were self-reported and may have been over- or underestimated and less accurate than data from surveys such as NHANES. Although the validity of the water intake question in FAB has not been determined, a recent study among adults found no significant difference between water intake that was self-reported on a questionnaire (on which the question was worded similarly to the question on the FAB) and water intake determined through 4-day food intake records ( r = 0.7) (29). BMI data in FAB are determined on the basis of self-reported weight and height and subject to reporting bias; however, measured and self-reported BMI are highly correlated among adults ( r > 0.9) (30). Finally, because the FAB data set did not include data about intake of calorically or artificially sweetened beverages, milk, or alcohol, we were unable to assess the relationship between intake of water and these beverages.

Approximately 7% of respondents reported drinking no water daily, and nearly half reported drinking less than 4 cups per day. Low drinking water intake was associated with various unhealthful behaviors, including low levels of physical activity and low levels of fruit and vegetable intake. Models controlling for sociodemographics indicated that attitudes about eating and health, as well as food-related behaviors such as eating meals while watching television, were also related to low drinking water intake. Further studies of population samples with greater ability to assess differences in water intake by race/ethnicity subgroups (eg, Hispanics, Asians) are needed, as is research to learn where people consume drinking water, such as homes, worksites, or community venues. Our results suggest that low drinking water intake is common and is associated with known unhealthful behaviors. Clinical and public health practitioners aiming to help people drink more water should consider low water intake as part of a group of unhealthful behaviors and attitudes.

Corresponding Author: Alyson B. Goodman, MD, MPH, Division of Nutrition, Physical Activity, and Obesity, Centers for Disease Control and Prevention, 4770 Buford Highway, NE, Atlanta, GA 30341, USA, Mailstop K-26. E-mail: [email protected] .

Author Affiliations: Heidi M. Blanck, Bettylou Sherry, Sohyun Park, Centers for Disease Control and Prevention, Atlanta, Georgia; Linda Nebeling, National Cancer Institute, Washington, DC; Amy L. Yaroch, Swanson Center for Nutrition, Omaha, Nebraska.

• Popkin B, D’Anci K, Rosenberg I. Water, Hydration and Health. Nutr Rev 2010;68(8):439–58. CrossRef PubMed
• Tate DF, Turner-McGrievy G, Lyons E, Stevens J, Erickson K, Polzien K, et al. . Replacing caloric beverages with water or diet beverages for weight loss in adults: main results of the Choose Healthy Options Consciously Everyday (CHOICE) randomized clinical trial. Am J Clin Nutr 2012;95(3):555-63. CrossRef PubMed
• Stookey J, Constant F, Popkin B, Gardner C. Drinking water is associated with weight loss in overweight dieting women independent of diet and activity. Obesity (Silver Spring) 2008;16(11):2481–8. CrossRef PubMed
• Stookey J, Constant F, Gardner C, Popkin B. Replacing sweetened caloric beverages with drinking water is associated with lower energy intake. Obesity (Silver Spring) 2007;15(12):3013–22. CrossRef PubMed
• Van Walleghen E, Orr J, Gentile C, Davy B. Pre-meal water consumption reduces meal energy intake in older but not younger subjects. Obesity (Silver Spring) 2007;15(1):93–9. CrossRef PubMed
• Daniels MC, Popkin BM. Impact of water intake on energy intake and weight status: a systematic review. Nutr Rev 2010;68(9):505–21. CrossRef PubMed
• Dennis EA, Dengo AL, Comber DL, Flack KD, Savla J, Davy KP, Davy BM. Water consumption increases weight loss during a hypocaloric diet intervention in middle-aged and older adults. Obesity (Silver Spring) 2010;18(2):300–7. CrossRef PubMed
• Akers JD, Cornett RA, Savla JS, Davy KP, Davy BM. Daily self-monitoring of body weight, step count, fruit/vegetable intake, and water consumption: a feasible and effective long-term weight loss maintenance approach. J Acad Nutr Diet 2012;112:685-92 e2.
• Duffey KJ, Popkin BM. Shifts in patterns and consumption of beverages between 1965 and 2002. Obesity (Silver Spring) 2007;15(11):2739–47. CrossRef PubMed
• Popkin BM, Armstrong LE, Bray GM, Caballero B, Frei B, Willett WC. A new proposed guidance system for beverage consumption in the United States. Am J Clin Nutr 2006;83(3):529–42. PubMed
• US Department of Agriculture, US Department of Health and Human Services. Dietary Guidelines for Americans 2010. 7th edition. Washington (DC): US Government Printing Office; 2010.
• Healthy beverages community action kit. Washington (DC): Indian Health Service; 2006.
• Promoting healthy youth: a parent toolkit for enhancing nutrition and physical activity in schools and at home. Ohio Action for Healthy Kids Association. http://www.ohioactionforhealthykids.org.
• Sebastian RS, Wilkinson Enns C, Goldman JD. Drinking water intake in the US: what we eat in America, NHANES 2005-2008. Food Surveys Research Group Dietary data brief no. 7; 2011. http://ars.usda.gov/Services/docs.htm?docid=19476.
• Kant AK, Graubard BI, Atchison EA. Intakes of plain water, moisture in foods and beverages, and total water in the adult US population — nutritional, meal pattern, and body weight correlates: National Health and Nutrition Examination Surveys 1999-2006. Am J Clin Nutr 2009;90(3):655–63. CrossRef PubMed
• Institute of Medicine. Dietary reference intakes for water, potassium, sodium, chloride, and sulfate. Institute of Medicine Panel on Dietary Reference Intakes for Electrolytes and Water, Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. Washington (DC): National Academies Press; 2005.
• Popkin BM, Barclay DV, Nielsen SJ. Water and food consumption patterns of US adults from 1999 to 2001. Obes Res 2005;13(12):2146–52. CrossRef PubMed
• Erinosho TO, Moser RP, Oh AY, Nebeling LC, Yaroch AL. Awareness of the fruits and veggies — More Matters campaign, knowledge of the fruit and vegetable recommendation, and fruit and vegetable intake of adults in the 2007 Food Attitudes and Behaviors (FAB) Survey. Appetite 2012;59(1):155–60. CrossRef PubMed
• National Obesity Education Initiative. Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults. Washington (DC): National Heart, Lung, and Blood Institute; 1998.
• Physical Activity Guidelines Advisory Committee. Physical Activity Guidelines Advisory Committee report, 2008. Washington (DC): US Department of Health and Human Services; 2008.
• Zizza CA, Ellison KJ, Wernette CM. Total water intakes of community-living middle-old and oldest-old adults. J Gerontol A Biol Sci Med Sci 2009;64(4):481–6. CrossRef PubMed
• Jones AQ, Dewey CE, Dore K, Majowicz SE, McEwen SA, Waltner-Toews D. Drinking water consumption patterns of residents in a Canadian community. J Water Health 2006;4(1):125–8. PubMed
• Park S, Sherry B, O’Toole T, Huang Y. Factors associated with low drinking water intake among adolescents: the Florida Youth Physical Activity and Nutrition Survey, 2007. J Am Diet Assoc 2011;111(8):1211–7. CrossRef PubMed
• Drinking water intake. In: Exposures factors handbook. Washington (DC): Environmental Protection Agency; 1997.
• Kant AK, Graubard BI. Contributors of water intake in US children and adolescents: associations with dietary and meal characteristics — National Health and Nutrition Examination Survey 2005-2006. Am J Clin Nutr 2010;92(4):887–96. CrossRef PubMed
• Smoking cessation. Blue Cross Blue Shield of Massachusetts; 2008. http://wwwbluecrossmacom/blue-iq/pdfs/83233-smoking-cessation-eipdf.
• Himes JH. Challenges of accurately measuring and using BMI and other indicators of obesity in children. Pediatrics 2009;124(Suppl 1):S3–22. CrossRef PubMed
• Stommel M, Schoenborn CA. Accuracy and usefulness of BMI measures based on self-reported weight and height: findings from the NHANES & NHIS 2001-2006. BMC Public Health 2009;9:421. CrossRef PubMed
• Hedrick VE, Comber DL, Estabrooks PA, Savla J, Davy BM. The beverage intake questionnaire: determining initial validity and reliability. J Am Diet Assoc 2010;110(8):1227–32. CrossRef PubMed
• McAdams MA, Van Dam RM, Hu FB. Comparison of self-reported and measured BMI as correlates of disease markers in US adults. Obesity (Silver Spring) 2007;15(1):188–96. CrossRef PubMed

Table 1. Respondents’ Characteristics, Reported Daily Drinking Water Intake, and Adjusted Odds of Drinking Less Than 4 Cups Daily, Food Attitudes and Behaviors Survey, United States, 2007

Abbreviations: AOR, adjusted odds ratio; CI, confidence interval; NA, not applicable; BMI, body mass index. a Chi-square tests were used for each variable to examine differences across categories. b The final logistic regression model included variables in 1 model to adjust for possible confounders and included a sample of 2,635 adults with complete data for all variables. c Of the total study sample (3,251), 5% were Hispanic, 2% Asian, 3% American Indian/Native Hawaiian, and 1% mixed race.

Table 2. Eating-Related Behaviors, Reported Daily Drinking Water Intake, and Adjusted Odds of Drinking Less Than 4 Cups Daily, by Respondents’ Preferences, Food Attitudes and Behaviors Survey, United States, 2007

Abbreviations: OR, odds ratio; CI, confidence interval. a Chi-square tests were used for each variable to examine differences across categories. b Multivariable logistic regression model included exposure variable and age, sex, race/ethnicity, education, income and region.

Table 3. Attitudes and Beliefs Related to Eating and Health, Reported Daily Drinking Water Intake, and Adjusted Odds Ratios of Drinking Less Than 4 Cups Daily, by Respondents’ Attitudes, Food Attitudes and Behaviors Survey, United States, 2007

Abbreviations: OR, odds ratio; CI, confidence interval. a Chi-square tests were used for each variable to examine differences across categories. b The multivariable logistic regression model included 1 exposure variable and age, sex, race/ethnicity, education, annual household income, and region.

File Formats Help:

• PCD podcasts
• PCD on Facebook
• Page last reviewed: April 25, 2013
• Page last updated: April 25, 2013
• Content source: National Center for Chronic Disease Prevention and Health Promotion
• Using this Site
• Contact CDC

Try our favorite, clean protein powder: See our top pick →

• Editorial Policy

Last updated on December 25, 2023

Is Drinking Water While Eating Bad?

Evidence Based Research To fulfill our commitment to bringing our audience accurate and insightful content, our expert writers and medical reviewers rely on carefully curated research. Read Our Editorial Policy

Claims Against Drinking While Eating

Claims in support, researchers weigh in, our verdict.

The verdict is definitely muddled on this one, but we at least know that the amount of water consumed and the timing of the meal can influence the health effects of drinking while eating.

To question something so well-ingrained into centuries-old mealtime norms may seem foolish at first, but modern science grants free passes to no one.

As such, several of the claims made by a quiet, but steadily growing community about the pitfalls of drinking water while eating have been responded to in a series of research findings.

First, let’s lay out the battleground on which this scuffle is taking place, starting with what the objectors are claiming about drinking while eating.

Opponents of solid-liquid meals believe that the practice can dilute stomach acids, increase bloat, and more.

Since water usually has a neutral pH of around 7, pouring it into an acidic solution will indeed decrease acidity , raising the pH closer to neutral.

Objectors to solid-liquid meals believe that this effect holds true in the case of our stomach acids, which are instrumental in breaking down nutrients.

This brings us to objection #1: Drinking while eating dilutes stomach acids, impairing digestion. 

The Dreaded Post-Meal Bloat

It may seem like a simple issue, but bloating after a meal or any other time can result from several underlying conditions and nutritional choices (i.e., too much sodium or too many refined carbs).

Still, many people believe that drinking water before, during, or soon after a meal can worsen this annoying and occasionally worrisome symptom. 

Exacerbates GERD

Gastroesophageal reflux disease (GERD), also known as acid reflux , has a complex relationship with mealtime water consumption.

On the one hand, too much water may cause stomach contents to rise into the esophagus, and on the other, smaller amounts can neutralize and wash away acids in this same scenario.

This is arguably the most salient point offered by the objectors—that water at mealtime worsens GERD symptoms —but it’s not as simple as that. 

What the naysayers call bloating, the pro-water-with-meals crowd refers to as a feeling of fullness .

They claim that this feeling of fullness promotes weight loss by preventing overeating.

Overeating Prevention

This claim goes hand-in-hand with the previous one; when you drink water with a meal, you naturally eat slower.

Supporters of solid-liquid meals believe that slowing down gives your satiety hormones (ghrelin and leptin) more time to make you feel full.

In other words, speed is a critical component to overeating, since it takes a few minutes for these hormones to kick in and make you feel full. 

Constipation and Stool Softening

Pair water with a fiber-rich meal, say liquid-solid meal supporters, and trips to the bathroom will be much easier.

Water is an essential stool softener, and if the body can’t draw enough of it into the colon at the right time, you’ll miss your window and deal with the consequences soon after.

Now that we know what each side is claiming, it’s time to turn to the science for an objective perspective. 

As it turns out, the jury is stacked in support of solid-liquid meals, but not without a few lingering possibilities of doubt.

Let’s start with the big one: digestion.

Drinking Water With Meals Doesn’t Impair Digestion

The claim that drinking water dilutes stomach acids is heavily oversimplified, explains this finding from the Gastroenterology Unit of the Mayo Clinic in Rochester, MN. 

Per the study, “S (solid-liquid) meals elicited a stronger early gastric secretory response (acid, pepsin, and volume) which compensated for faster initial emptying and resulted in higher gastric acidity and volume than after H (homogenized) meals.”

In other words, while water will always neutralize acids, the body is equipped with a compensatory mechanism that allows for normal digestion of solid-liquid meals. 

“Gastric Emptying Rate” of Food Is Unaffected by Water 

The term “gastric emptying” refers to the amount of time food spends in the stomach before it empties into the small intestine; it’s accepted as a measure of digestion efficiency .

According to a finding from the Temple University School of Medicine in Philadelphia, water consumed concurrently with food does not affect the food’s gastric emptying rate.

Conversely, food was found to significantly impact the gastric emptying rate of water, but this is understandably less troublesome than the opposite scenario. 

Drinking Before Meals Prevents Overeating

In another finding featuring 24 obese participants, 500mL of water consumed half an hour before a meal resulted in a 13% reduction in “meal energy intake.”

It’s also important to note that this effect was observed equally across age groups, genders, and BMI levels.

Not to mention, consuming water before a meal will create a favorable environment for water-soluble vitamins like vitamin C, thiamin, and many others.

Speed Matters

Finally, the link between speed and overeating was objectively confirmed by a study from Texas Christian University that compared total energy intake, satiety, and energy density (calories absorbed per gram of food/water) across two eating speeds.

The researchers found that normal-weight participants who slowly consumed food ingested fewer calories and felt fuller one hour after the meal began, but this didn’t hold true with obese participants. 

It’s just conjecture, but this discrepancy hints at hormonal elements in play, since obese participants who ate slower apparently did not respond as well to the satiety hormones.

For or against, almost every piece of evidence related to this topic points to quantity of water consumed and timing as key factors that can sway results. 

The evidence is also clouded by subjectivity in many cases, like feelings of satiety reported in weight-loss-focused studies.

Not accounting for these complications, we’re inclined to side with the majority of the research, which claims that drinking water before, during, and after meals is just fine.

As with all things, consume moderately, slow down, and enjoy yourself. 

You Might Also Like

Stress-Eat the Proper Way with Ashwagandha

Ashwagandha is a small, bushy plant native to India, the Middle East, and some regions of Africa.

The Most Common Nutritional Deficiencies

Sugar, salt, and fat have presided over the American food industry as a tyrannical threesome for some time now, and thanks to their massive success, they’re well cemented into the infrastructure.

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Save my name, email, and website in this browser for the next time I comment.

Popular in Miscellaneous

TNI Editorial Team

Nutrition Psychiatry: How Food Impacts Mental Health

Food is for physical wellness, and pharmaceutical products are for mental health conditions—that’s where most of us land when it comes to nutrition psychiatry.

Nutrition is understandably not priority one in the chaotic moments immediately following a traumatic brain injury (TBI), but as soon as the patient is stable, nutrition therapy shares center stage with other key tenets of TBI rehabilitation.

Nutrition’s Role in Traumatic Brain Injury Recovery

Yes, These Foods Contain Added Sugars

Normally, we’re content to bounce around new and/or controversial theories on nutritional concepts all day, but every so often, we have the luxury of seeing in black and white.

This may seem like a fun-killing exercise at first, but we’re not interested in coddling or pandering to our readers, so let’s get the harsh reality out of the way: most of us haven’t earned the right to binge on vacation.

The Vacationer’s Guide to Healthy Eating

Introducing the Ultimate Hair-Growth Diet

Nutrition is for losing belly fat, and overpriced, medicated goop is for hair loss—that’s how most of us are conditioned to think.

Want more juicy nutrition tips?

Subscribe now and never miss anything about the topics important to you and your health.

There are many options for what to drink , but water is the best choice for most people who have access to safe drinking water. It is calorie-free and as easy to find as the nearest tap.

Water helps to restore fluids lost through metabolism, breathing, sweating, and the removal of waste. It helps to keep you from overheating, lubricates the joints and tissues, maintains healthy skin, and is necessary for proper digestion. It’s the perfect zero-calorie beverage for quenching thirst and rehydrating your body.

How Much Water Do I Need?

Water is an essential nutrient at every age, so optimal hydration is a key component for good health. Water accounts for about 60% of an adult’s body weight. We drink fluids when we feel thirst, the major signal alerting us when our body runs low on water. We also customarily drink beverages with meals to help with digestion. But sometimes we drink not based on these factors but on how much we think we should be drinking. One of the most familiar sayings is to aim for “8 glasses a day,” but this may not be appropriate for every person.

General recommendations

• The National Academy of Medicine suggests an adequate intake of daily fluids of about 13 cups and 9 cups for healthy men and women, respectively, with 1 cup equaling 8 ounces. [1] Higher amounts may be needed for those who are physically active or exposed to very warm climates. Lower amounts may be needed for those with smaller body sizes. It’s important to note that this amount is not a daily target, but a general guide. In the average person, drinking less will not necessarily compromise one’s health as each person’s exact fluid needs vary, even day-to-day.
• Fever, exercise, exposure to extreme temperature climates (very hot or cold), and excessive loss of body fluids (such as with vomiting or diarrhea) will increase fluid needs.
• The amount and color of urine can provide a rough estimate of adequate hydration. Generally the color of urine darkens the more concentrated it is (meaning that it contains less water). However, foods, medications, and vitamin supplements can also change urine color. [1] Smaller volumes of urine may indicate dehydration, especially if also darker in color.
• Alcohol can suppress anti-diuretic hormone, a fluid-regulating hormone that signals the kidneys to reduce urination and reabsorb water back into the body. Without it, the body flushes out water more easily. Enjoying more than a couple of drinks within a short time can increase the risk of dehydration, especially if taken on an empty stomach. To prevent this, take alcohol with food and sips of water.
• Although caffeine has long been thought to have a diuretic effect, potentially leading to dehydration, research does not fully support this. The data suggest that more than 180 mg of caffeine daily (about two cups of brewed coffee) may increase urination in the short-term in some people, but will not necessarily lead to dehydration. Therefore, caffeinated beverages including coffee and tea can contribute to total daily water intake. [1]

Keep in mind that about 20% of our total water intake comes not from beverages but from water-rich foods like lettuce, leafy greens, cucumbers, bell peppers, summer squash, celery, berries, and melons.

Aside from including water-rich foods, the following chart is a guide for daily water intake based on age group from the National Academy of Medicine:

Preventing Dehydration: Is Thirst Enough?

As we age, however, the body’s regulation of fluid intake and thirst decline. Research has shown that both of these factors are impaired in the elderly. A Cochrane review found that commonly used indicators of dehydration in older adults (e.g., urine color and volume, feeling thirsty) are not effective and should not be solely used. [3] Certain conditions that impair mental ability and cognition, such as a stroke or dementia, can also impair thirst. People may also voluntarily limit drinking due to incontinence or difficulty getting to a bathroom. In addition to these situations, research has found that athletes, people who are ill, and infants may not have an adequate sense of thirst to replete their fluid needs. [2] Even mild dehydration may produce negative symptoms, so people who cannot rely on thirst or other usual measures may wish to use other strategies. For example, aim to fill a 20-ounce water bottle four times daily and sip throughout the day, or drink a large glass of water with each meal and snack.

Symptoms of dehydration that may occur with as little as a 2% water deficit:

• Confusion or short-term memory loss
• Mood changes like increased irritability or depression

Dehydration can increase the risk of certain medical conditions:

• Urinary tract infections
• Kidney stones
• Constipation  

Like most trends of the moment, alkaline water has become popular through celebrity backing with claims ranging from weight loss to curing cancer. The theory behind alkaline water is the same as that touting the benefits of eating alkaline foods, which purportedly counterbalances the health detriments caused by eating acid-producing foods like meat, sugar, and some grains.

From a scale of 0-14, a higher pH number is alkaline; a lower pH is acidic. The body tightly regulates blood pH levels to about 7.4 because veering away from this number to either extreme can cause negative side effects and even be life-threatening. However, diet alone cannot cause these extremes; they most commonly occur with conditions like uncontrolled diabetes, kidney disease, chronic lung disease, or alcohol abuse.

Alkaline water has a higher pH of about 8-9 than tap water of about 7, due to a higher mineral or salt content. Some water sources can be naturally alkaline if the water picks up minerals as it passes over rocks. However, most commercial brands of alkaline water have been manufactured using an ionizer that reportedly separates out the alkaline components and filters out the acid components, raising the pH. Some people add an alkaline substance like baking soda to regular water.

Scientific evidence is not conclusive on the acid-alkaline theory, also called the acid-ash theory, stating that eating a high amount of certain foods can slightly lower the pH of blood especially in the absence of eating foods supporting a higher alkaline blood pH like fruits, vegetables, and legumes. Controlled clinical trials have not shown that diet alone can significantly change the blood pH of healthy people. Moreover, a direct connection of blood pH in the low-normal range and chronic disease in humans has not been established.

BOTTOM LINE: If the idea of alkaline water encourages you to drink more, then go for it! But it’s likely that drinking plain regular water will provide similar health benefits from simply being well-hydrated—improved energy, mood, and digestive health

Is It Possible To Drink Too Much Water?

There is no Tolerable Upper Intake Level for water because the body can usually excrete extra water through urine or sweat. However, a condition called water toxicity is possible in rare cases, in which a large amount of fluids is taken in a short amount of time, which is faster than the kidney’s ability to excrete it. This leads to a dangerous condition called hyponatremia in which blood levels of sodium fall too low as too much water is taken. The excess total body water dilutes blood sodium levels, which can cause symptoms like confusion, nausea, seizures, and muscle spasms. Hyponatremia is usually only seen in ill people whose kidneys are not functioning properly or under conditions of extreme heat stress or prolonged strenuous exercise where the body cannot excrete the extra water. Very physically active people such as triathletes and marathon runners are at risk for this condition as they tend to drink large amounts of water, while simultaneously losing sodium through their sweat. Women and children are also more susceptible to hyponatremia because of their smaller body size.

Fun Flavors For Water  

Infused water

Instead of purchasing expensive flavored waters in the grocery store, you can easily make your own at home. Try adding any of the following to a cold glass or pitcher of water:

• Sliced citrus fruits or zest (lemon, lime, orange, grapefruit)
• Crushed fresh mint
• Peeled, sliced fresh ginger or sliced cucumber
• Crushed berries

Sparkling water with a splash of juice

Sparkling juices may have as many calories as sugary soda. Instead, make your own sparkling juice at home with 12 ounces of sparkling water and just an ounce or two of juice. For additional flavor, add sliced citrus or fresh herbs like mint.

TIP: To reduce waste, reconsider relying on single-use plastic water bottles and purchase a colorful 20-32 ounce refillable water thermos that is easy to wash and tote with you during the day. 

Are seltzers and other fizzy waters safe and healthy to drink?

BOTTOM LINE: Carbonated waters, if unsweetened, are safe to drink and a good beverage choice. They are not associated with health problems that are linked with sweetened, carbonated beverages like soda.

• Harvard T.H. Chan School of Public Health is a member of the Nutrition and Obesity Policy Research and Evaluation Network’s (NOPREN) Drinking Water Working Group. A collaborative network of the Centers for Disease Control and Prevention, the NOPREN Drinking Water Working Group focuses on policies and economic issues regarding free and safe drinking water access in various settings by conducting research and evaluation to help identify, develop and implement drinking-water-related policies, programs, and practices. Visit the network’s website to access recent water research and evidence-based resources.
• The Harvard Prevention Research Center on Nutrition and Physical Activity provides tools and resources for making clean, cold, free water more accessible in environments like schools and afterschool programs, as well as tips for making water more tasty and fun for kids.
• The National Academy of Sciences. Dietary References Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. https://www.nap.edu/read/10925/chapter/6#102 Accessed 8/5/2019.
• Millard-Stafford M, Wendland DM, O’Dea NK, Norman TL. Thirst and hydration status in everyday life. Nutr Rev . 2012 Nov;70 Suppl 2:S147-51.
• Hooper L, Abdelhamid A, Attreed NJ, Campbell WW, Channell AM, et al. Clinical symptoms, signs and tests for identification of impending and current water-loss dehydration in older people. Cochrane Database Syst Rev . 2015 Apr 30;(4):CD009647.

Terms of Use

The contents of this website are for educational purposes and are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. The Nutrition Source does not recommend or endorse any products.

The Gut Health Clinic

Special clinic discount: 20% off initial online consultations booked in April with SPRING20

Eat More, Live Well

In her latest book, Dr Megan Rossi (PhD, RD) shares everything you need to know about boosting gut health and plant-based eating

Eat Yourself Healthy

Dr Megan Rossi explains how to feed your gut for a happier, healthier you using delicious, gut-boosting recipes

Bloating Masterclass now open!

Back due to popular demand. Don’t miss out on Dr Megan Rossi’s Bloating Masterclass: comprehensive training + toolkit

Book resources

In Dr Megan Rossi's two books, you will find references to materials and assessments that can be downloaded here

Dr Megan Rossi realised that there was a gap in the market for breakfast foods that truly deliver on gut health promises

My Gut Diary and Gut Health Assessments Booklet can help kickstart your gut health transformation

Home / Learn / Drinking water with meals: yay or nay?

Drinking water with meals: yay or nay?

By The Gut Health Doctor Team

Related articles

5 February 2024

7 science-backed things to know about bloating

2 February 2024

By Gabrielle Morse

The key principles of intuitive eating

22 December 2023

By Lucy Kerrison

Five top tips to prevent Christmas constipation

Sign up for our free newsletter & gut health guide

Not sure where to start on your gut health transformation? Sign up for free and we’ll empower you every month with the latest educational blogs, gut-loving recipes, research updates and helpful resources delivered straight to your inbox. You’ll also receive a  downloadable guide with an intro to gut science, practical advice and exclusive recipes. Lots of support and no spam.

Free gut health guide

Join our community for gut-loving recipes, research, resources and a free gut health guide. Lots of support and no spam.

© Copyright 2024 The Gut Health Doctor | Website by Union 10 Design

• Search the site Please fill out this field.
• Saved Items & Collections
• Add a Recipe
• Manage Your Subscription
• Give a Gift Subscription
• Newsletters
• Sweepstakes
• Kitchen Tips

Is It Bad to Drink Water While Eating?

Plus, get the scoop on whether it affects your poop.

Mary Claire Lagroue works as an associate commerce editor at Food & Wine. A former associate editor at Allrecipes, she joined Dotdash Meredith in 2019. She has written about food since 2017, and her work can be found in Cooking Light, Southern Living, and more.

For many, no meal is complete without a cool, refreshing glass of H2O. After all, who wants to dig into a plate of salty or spicy food without a glass of water to wash it down? But should you drink water while eating? Is it healthy? Does it cause digestive issues? And what about drinking water before or after eating?

Is It OK to Drink Water While You Eat?

First, let's dispel the main myth here, that drinking water with your food leads to digestive issues, from the body not absorbing nutrients to bloating. In short, drinking water doesn't mess with digestion, says Michael F. Picco, M.D. , of the Mayo Clinic.

The misconception boils down to the belief that water dilutes stomach acid. The stomach adapts to whatever's in it, however, so it will produce more acid if needed. In other words, drinking water before, during, or after a meal won't keep the stomach from doing its job.

On the contrary, drinking water actually improves digestion, helping food move more easily through the digestive system, according to the Cleveland Clinic . Too little water in the body can actually cause constipation.

After food and liquid leave the stomach, water and digested nutrients enter the bloodstream through the small intestine, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Next, the large intestine absorbs the water that remains and uses it to form stools. Because water softens stools, drinking plenty of water eases constipation.

Other myths you may come across say that drinking water with meals can cause acid reflux or raise insulin levels. To be sure, if you have acid reflux or astroesophageal reflux disease (GERD), you may want to limit the amount of water you consume in one sitting to prevent excess pressure on your stomach, Johns Hopkins suggests. Sticking to flat water over sparkling helps, too. Drinking water doesn't cause these conditions, though.

Finally, if you're concerned about maintaining insulin levels, don't put that glass of water down. Your blood sugar can rise due to several surprising factors — including artificial sweeteners and coffee — but water isn't one of them. Dehydration, however, does lead to higher blood sugar levels, the CDC says.

All in all, drinking water keeps the body hydrated and healthy. So, please, keep filling your glass to your heart's (or stomach's) content.

You’ll Also Love

You’re Probably Drinking Too Much Water — Here’s Why

Humans get about 20 percent of their water from food.

Staying hydrated is a Sisyphean task. The water bottle craze only exemplifies the never-ending demand for drinking enough water. While the axiom that everyone needs to drink 8 ounces of water 8 times a day has been debunked many times over , nobody will dispute that getting enough water is vital for everything from good bowel movements to proper body temperature and healthy joints.

But there’s a way to hydrate without lugging around a trendy Stanley tumbler. Tweaking the way you eat and adding certain foods accounts for more water than you might realize.

The benefits of eating your water

Most foods contain some amount of water, so our diet provides significant hydration. A 2010 paper , a 2007 study in the Journal of the American College of Nutrition , and a 2016 European Hydration Research Study all approximate that 20 to 25 percent of our water comes from our food. These other sources do double duty of hydrating and providing nutrients as critical as water.

Which foods are the most hydrating?

Fruits and veggies are, perhaps unsurprisingly, the best water bombs to enjoy, but the breakdown among them may be surprising.

Cantaloupe, strawberries, watermelon (it’s literally in the name), lettuce, cabbage, celery, spinach, pickles, and cooked squash all comprise 90 to 99 percent water. Following up are yogurt, apples, grapes, oranges, carrots, pears, pineapple, and cooked broccoli at 80 to 89 percent. Harvard T.H. Chan School of Public Health recommends piling half your plate with fruits and vegetables. This would help ensure that one-quarter to one-fifth of your water comes from your diet, plus all the dietary fiber that’s as important as hydration.

Cucumbers are 96 percent water, and iceberg lettuce beats out other leafy greens when it comes to H2O content. Tomatoes, bell peppers, cauliflower, and mushrooms make the water-intensive grade, too.

Showcasing that truly everything has water, the list from the 2010 paper includes some more surprising fare. These foods aren’t hydrating per se but may contain more water than you thought. The list includes pizza, which is between 40 and 49 percent water. Ice cream is between 60 and 69 percent water, beating out other dairy like cheddar cheese and butter (30 to 39 percent and 10 to 19 percent, respectively). Basic oils and sugar don’t contain any water, so dressing your iceberg lettuce won’t add any hydration.

While a massive reusable water bottle might seem intimidating, eating your water helps break down the process into bite-sized chunks.

What Exactly Can You Drink While Intermittent Fasting Without Breaking Your Fast?

Y ou’ve likely heard celebs and influencers tout the benefits of various trendy diets , but one buzzy eating plan continues to stay in the spotlight: intermittent fasting . People swear by the benefits of structuring *when* they eat and snack, but the fasting schedule begs a lot of questions. Are there side effects ? Will I lose weight ? Do I have to give up my morning coffee? What can I drink without breaking my fast?

The latter are the questions that bring us here today. Keep reading for everything you need to know about what you can—and can't—drink while fasting.

Why What You Drink During Intermittent Fasting Is So Important

“Many beverages have calories that can break your fast, trigger an insulin response, and prevent your body from going into autophagy , which is one of the benefits of fasting,” says Ana Reisdorf, RD , founder of The Food Trends .

That being said, it’s especially easy to become dehydrated while fasting (no matter what type of fast you’re on), says Reisdorf. “You may not realize, but a lot of your daily fluid needs come from food, and when you avoid eating for a period of time, this means you will need to drink more water or other calorie-free liquids to compensate," she explains.

Be intentional about your sipping and aim to drink at least 2.7 liters of water per day . The only time as much plain water as you want is not allowed is if you’re on a dry fast , which Reisdorf does not recommend and says can lead to severe dehydration.

What *Not* To Drink While Fasting

A good rule of thumb is to avoid any drinks that have any calories while you're fasting, says Erin Palinski-Wade, RD , author of 2 Day Diabetes Diet who is based in New Jersey .

This includes sweetened beverages, such as juice or soda, milk or other dairy-based beverages, and alcohol, says Reisdorf. Some schools of thought also recommend avoiding diet sodas, even though they are calorie-free, since artificial sweeteners can trigger an insulin response, she adds.

What You *Can* Drink While Fasting

Okay, but what you can actually drink when fasting may be a little hazy. And there are some surprising hacks that allow you to have some flavor without breaking your fast. (Think: adding spices to your coffee or a splash of fruit juice to your H20.)

Below, what you should know about some of the most popular drinks you might want to consume while doing intermittent fasting, and whether or not they'll sabotage your fasted state.

Meet the Experts: Ana Reisdorf, RD , is the founder of The Food Trends . Erin Palinski-Wade, RD , is the author of 2 Day Diabetes Diet. Regan Jones, RDN, ACSM-CPT , is the host of This Unmillennial Life.

Drink: Coffee

Black coffee is calorie-free, so it's fine to enjoy during the fasting phase. But adding in sugar, cream, or milk is best avoided, as it can add calories to the drink that can take you out of a fasted state.

“If you do want to flavor your coffee during a fast, experiment with calorie-free flavoring from a spice like cinnamon,” says Palinski-Wade. “Save the coffee add-ons for your non-fast windows of time."

Wondering about a keto-approved creamer or MCT oil? “This tends to be a little bit more controversial or at least open for interpretation depending on who you talk to,” says Regan Jones, RDN, ACSM-CPT , host of This Unmillennial Life.

"From a strict fasting standpoint, adding fats to your coffee does break the fast," Jones says. "But I actually do recommend high-quality MCT for people who are consistently doing day-to-day IF programs, especially if their goals are less about cutting calories and more about keeping blood glucose low and giving the body time to rest and digest.”

Fats do not have the same sort of blood glucose raising ability of carbohydrates or protein, so they do not really impact your fast if what you're trying to achieve is improving your overall insulin sensitivity, according to Jones. Plus, “Many people report better focus in the morning sipping coffee with MCT oil since the medium-chain fats in MCT oil get immediately converted to ketones, which are an alternative fuel source for the brain versus glucose.”

Additionally, avoid having more than one cup, or switch to decaf, when you're fasting. Excessive caffeine, especially on an empty stomach, may increase those jittery feelings which can often increase appetite and the desire to snack. Jones adds that caffeine raises cortisol which can “cause a cascade of hormonal responses that ultimately leads to an increase in blood glucose, [which is] something we are trying to avoid when fasting,” states Jones.

Just like coffee, tea is naturally calorie-free and fine to have during a fast, so long as it’s simply brewed tea that comes from tea bags, leaves, or flakes. Bottled ice tea is often heavily sweetened, so if you go that route, make sure you’re opting for one that is unsweetened and not loaded with added sugar and calories, says Palinski-Wade. Caloric add-ons such as honey, milk or cream should be reserved for non-fasting times, just like with coffee.

“Since tea is naturally lower in caffeine than coffee, you can have a bit more during fasts, however I would still recommend opting for decaf when possible,” she says.

Drink: Water and seltzer

Water is naturally calorie-free so there's no need to restrict it, says Palinski-Wade. Water in general is a good idea to sip on during fasting times to ensure hydration but also as a way to fill your stomach and prevent hunger.

If you enjoy flavored water, you can add in fruit wedges or a splash of lemon or lime juice (or a splash of another juice) as long as it is a true "splash" (around one tablespoon per 12 ounces) and doesn’t add more than a trivial amount of calories, says Palinski-Wade. Carbonated water/seltzer can be treated in the same way as water, as long as it is naturally flavored and calorie-free.

Skip: Apple cider vinegar

When it comes to fasting, many people think apple cider vinegar (ACV) or an apple cider vinegar tonic is okay to consume. According toJones, both ACV and bone broth have calories. "While minimal, the calories would ultimately lead to a metabolic breaking of the fast," says Jones.

However, if you really enjoy sipping ACV or an ACV tonic at other (non fasted) times, you're in luck. “If the goal is to simply reduce caloric intake overall throughout the day and give the body an extended period of digestive rest and lower insulin levels, I would say the ACV is less likely to raise insulin levels than bone broth,” Jones says.

Skip: Bone broth

Unfortunately, if you enjoy sipping on a warm mug of bone broth, you may want to wait until after you have finished your fast. “Bone broth, while very popular in paleo and some fasting circles, can be a nutritious and satisfying beverage, but it can also be a source of protein. Protein raises blood glucose, which raises insulin levels," says Jones. While protein won't impact blood sugar and insulin levels as much as carbohydrate, it will still break your fast.

If you're wondering if you can drink soda (or diet soda) while you're doing intermittent fasting, Palinski-Wade recommends staying away from soda in general, even if you’re not following a diet like intermittent fasting.

Regular sodas are usually loaded with sugar and calories and offer no nutritional value, she says. There also isn’t enough data and research to say whether diet soda is okay to drink during IF, but research suggests that consuming too many artificial sweeteners (as diet sodas tend to have) can increase cravings and appetite, as well as promote weight gain and the storage of fat.

“Your best bet is to limit all sodas as much as possible and satisfy carbonation cravings with seltzer or carbonated water,” she says.

Skip: Alcohol

Alcohol should never be consumed when in a fasting period, as its effects can be intensified when consumed on an empty stomach, says Palinski-Wade. Alcohol is also a source of calories, so drinking it would break your fast while also likely stimulating your appetite and leading to increased hunger and cravings.

Frequently Asked Questions

Who should try intermittent fasting?

Intermittent fasting is typically safe for most healthy people, but you should always consult with your doctor or a registered dietitian to see if it’s right for you, says Reisdorf. It is more important that certain groups avoid intermittent fasting, she adds.

People who should not do intermittent fasting include:

• Those with medical conditions, particularly metabolic disorders like diabetes
• Pregnant or breastfeeding women
• Children and teens
• Those who are underweight
• Those with a history of disordered eating
• Older adults who may have different nutritional needs

What are the pros of intermittent fasting?

Everyone is different and has unique needs, but intermittent fasting may lead to faster weight loss, improved body composition, and improved insulin sensitivity, says Reisdorf. On top of that, it’s a relatively easy plan to follow which involves less meal prep, she adds.

What are the cons of intermittent fasting?

Intermittent fasting may be too restrictive and difficult to sustain for some, says Reisdorf. In the same vein, it can trigger disordered eating and unhealthy eating patterns, she adds. It’s also not recommended for those with underlying health conditions or nutritional deficiencies.

What is the best thing to drink when intermittent fasting?

Plain water, black coffee , and unsweetened tea are the best beverages to sip while fasting, says Reisdorf. At the end of the day, you want to consume close to zero calories during fasting periods. By avoiding sweetened drinks like soda and bottled iced tea, as well as caloric add-ons in your hot beverages, you can ensure you follow your IF plan correctly and successfully.

What should you eat while intermittent fasting?

It’s clear that what you drink while fasting contributes to your success, but what you eat (when you're not actually fasting!) is also key. A main perk of intermittent fasting is that you technically don’t have to alter what you eat, you just have to eat within a certain window of time.

That said, you want to be sure your meals are well-balanced, says Reisdorf. Prioritize fruits, vegetables, and protein during your feeding window, and focus on foods that are high in fiber and healthy fats, she adds. Think quinoa, spinach, apples, avocado, salmon, almonds, sweet potato, and chicken.

You also want to avoid or minimize processed foods, simple carbs, refined sugars, and sugary drinks.

What about taking supplements during a fasting period?

This depends on the fasting schedule you're following, and you should discuss any supplements with your doctor before beginning to take them, says Palinski-Wade. If you fast for a set amount of hours each day, take your supplements during the eating hours (unless otherwise instructed by your doctor or dietitian), since most supplements like a multivitamin are better absorbed when taken with food.

If you practice intermittent fasting that involves fasting on specific days, like the 5:2 diet, taking supplements is still recommended to ensure you are meeting your nutrient needs each day. Palinski-Wade recommends taking a high-quality multivitamin daily when following any IF plan.

“Generally, the small amount of calories found in a chewable/gummy/liquid vitamin would not offset a fast day,” she says. "But do discuss this with your doctor or dietitian first to make sure you can take your supplement on an empty stomach.”

Types Of Intermittent Fasting

Consider these different types of fasting that focus on *when* you can eat. Remember: Always talk to your doctor before overhauling your eating regimen and know that we’re not necessarily endorsing these strategies, just shedding some light on what they involve.

16/8 Method: This is the most popular method that involves fasting for 16 hours each day and limiting your eating window to eight hours, says Reisdorf. This is relatively easy to follow since it usually involves skipping breakfast and having your first meal around noon, she adds.

5:2 Diet: With this plan, you eat “normally” for five days a week and restrict calorie intake to 500 to 600 calories for two non-consecutive days, says Reisdorf.

Eat-Stop-Eat: This method involves fasting for 24 hours once or twice a week, says Reisdorf. So, you would eat dinner one day and fast all the way until dinner the next day.

Alternate-Day Fasting: This method involves fasting every other day, Reisdorf explains. On fasting days, calorie intake is either restricted to 500 to 600 calories or completely avoided, she adds.

OMAD (One Meal a Day): OMAD involves fasting for approximately 23 hours and consuming all your daily calories within a one-hour eating window, explains Reisdorf. This is the most extreme form of fasting.

Try 200+ at home workout videos from Men’s Health, Women’s Health, Prevention, and more on All Out Studio free for 14 days!

• Português Br
• Journalist Pass

Mayo Clinic Minute: Tips to make colonoscopy bowel prep easier

Share this:.

For many people, one of the most uncomfortable parts of a  colonoscopy  is the preparation for the procedure. The purpose of a colonoscopy is to examine the colon and rectum for abnormalities such as polyps, tumors or inflammation, aiding in the detection and prevention of  colorectal cancer . And to do that, it's important your medical team has a clear view.  Dr. Derek Ebner, a Mayo Clinic  gastroenterologist , offers tips on how to make colonoscopy bowel prep, essentially a strong laxative, easier.

Watch: The Mayo Clinic Minute

Journalists: Broadcast-quality video pkg (1:09) is in the downloads at the end of the post. Please "Courtesy: Mayo Clinic News Network." Read the  script.

"The entire spirit of doing the colonoscopy prep is to make sure that there is nothing in the colon," says Dr. Ebner.

That's so your medical team can detect and remove  polyps  or lesions.

"We frequently hear that the colon preparation can be a challenge," he says.

When to start bowel prep

Review your prep guidelines one to two weeks before your procedure for any special instructions. You may be encouraged to make small changes in your diet starting a week before the procedure.

Often, the day before the colonoscopy is when you'll start the bowel prep solution. Dr. Ebner says this is where people may struggle.

Tips for taking bowel prep solution

"There's a couple of tricks. Often, cooling the solution and drinking it through a straw can be helpful. Others like to have a small lime or lemon wedge that they just bite into after doing some of the solution," says Dr. Ebner.

Chewing gum between sips of the solution also may help. And he says taking the solution is often spread out over two days, and that can help too.

"Half of the volume is done the day before the procedure, the other half is done the day of the procedure. That helps make it a lot more tolerable. And, in fact, we get a better cleanout by doing that splitting," he says.

Dr. Ebner says some adnominal cramping, bloating, discomfort or nausea during the bowel preparation is normal. "For those that do have nausea, slowing down how fast you're consuming the fluid can oftentimes be really helpful," he says. 

Related posts:

• Mayo Clinic Minute: Warning signs of colorectal cancer in younger adults
• Mayo Clinic Minute: What’s the right colorectal cancer screening option for you?
• Melatonin use in children: Is a sleep aid supplement safe? Untangling the threads of early onset dementia

Related Articles

Couples Who Drink Together Will Live Longer, According To Study

Drink up, honey!

There are plenty of factors that contribute to a long lifespan: healthy diet, family history, exercise, and...drinking with your significant other, apparently.

University of Michigan research professor Dr. Kira S. Birditt was inspired by a theory called "the drinking partnership," which claims that couples who have these similar drinking habits also have healthier marriages. Her new study is a deeper dive into her existing research from 2016.

"We're not sure why this is happening," Dr. Birditt previously said, "but it could be that couples that do more leisure time activities together have better marital quality."

In the original survey, she sourced 3,000 couples who had been married for around 33 years. She found that the couples who drank together were happier and stay together longer than the couples in marriages where only one partner drank.

"The purpose of this study was to look at alcohol use in couples in the Health and Retirement Study and the implications for mortality," Birditt says, according to Science Daily . The study included adults 50 years and older across the U.S. with 4,656 married, different-sex couples. They were reportedly interviewed every two years before Birditt made the conclusions.

While the study didn't analyze the specific amount or type of alcohol couples were enjoying, the polled participants were asked whether they had consumed an alcoholic beverage with their partner in the last three months. Those who indicated drinking together during that time period ultimately lived longer than those that did not.

"We don’t know why both partners drinking is associated with better survival," Birditt says. "Behaviors that are good for marriage are not necessarily good for health. There is also little information about the daily interpersonal processes that account for these links. Future research should assess the implications of couple drinking patterns for daily marital quality, and daily physical health outcomes."

Cheers to that!

David Chang Wants To Own The Term 'Chili Crunch'

Walmart Could Owe You Up To $500

Starbucks And Dunkin' Sued Over Non-Dairy Milk Fee

Chick-fil-A Is Testing Out A New Sandwich

This Easy Hack Makes White Bread Healthier

Burger King Releases New Cotton Candy Frozen Drink

Fast Food Prices Have Skyrocketed, New Study Shows

Supermarket Adds GPS Trackers To Meat Products

How Healthy Is It To Eat Meat Every Day?

Costco Is Offering Weight Loss Services & Ozempic

Anya Taylor-Joy's Wedding Cake Was Insane

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

• Publications
• Account settings

Preview improvements coming to the PMC website in October 2024. Learn More or Try it out now .

• Advanced Search
• Journal List

The impact of water consumption on hydration and cognition among schoolchildren: Methods and results from a crossover trial in rural Mali

Anna n. chard.

1 Department of Environmental Health, Emory University Rollins School of Public Health, Atlanta, Georgia, United States of America

Victoria Trinies

Caroline j. edmonds.

2 School of Psychology, University of East London, London, United Kingdom

Assitan Sogore

3 Monitoring, Evaluation, and Learning Section, Save the Children Mali, Bamako, Mali

Matthew C. Freeman

Associated data.

All relevant data are within the paper and its Supporting Information files.

Adequate provision of safe water, basic sanitation, and hygiene (WASH) facilities and behavior change can reduce pupil absence and infectious disease. Increased drinking water quantity may also improve educational outcomes through the effect of hydration on attention, concentration, and short-term memory. A pilot study was conducted to adapt field measures of short-term cognitive performance and hydration, to evaluate levels of hydration, and to investigate the impact of providing supplementary drinking water on the cognitive performance of pupils attending water-scarce schools in rural Mali. Using a cross-over trial design, data were collected under normal school conditions (control condition) on one visit day; on the other, participants were given a bottle of water that was refilled throughout the day (water condition). Morning and afternoon hydration was assessed using specific gravity and urine color. Cognitive performance was evaluated using six paper-based tests. Three percent of pupils were dehydrated on the morning of each visit. The prevalence of dehydration increased in the afternoon, but was lower under the water condition. Although there was a trend indicating drinking water may improve cognitive test performance, as has been shown in studies in other settings, results were not statistically significant and were masked by a “practice effect.”

Introduction

Health and educational benefits associated with improved water, sanitation, and hygiene (WASH) in schools include reduced diarrhea, absence, acute respiratory infection, and soil-transmitted helminth infection [ 1 – 5 ]. The availability of water during the school day is essential for supporting personal hygiene, sanitation, and maintaining a clean school environment. Increased access to water for drinking at school may also directly affect pupils’ academic performance through the cognitive benefits associated with decreased dehydration [ 6 – 8 ].

A recent UNICEF report found that only 53% of schools in least developed and other low-income countries had access to adequate water facilities, highlighting a gap in access to year-round, reliable, and safe water supply in sufficient quantities to support students’ needs [ 9 ]. Two studies assessing dehydration prevalence among school-age children living in hot, arid regions found that approximately two-thirds of children were in a state of moderate to severe dehydration [ 10 , 11 ].

The impact of dehydration on cognitive performance is well studied among adults in experimental settings. Dehydration induced through exercise or heat stress has been associated with decreased short-term memory [ 6 , 8 ], long-term memory [ 8 , 12 ], arithmetic efficiency [ 6 ], visuospatial function [ 6 ], and attention [ 7 ]. Few studies have investigated the relationship between dehydration and cognition in children. Evidence from three intervention studies in the United Kingdom corroborate findings among adults, suggesting that drinking water was associated with better scores of attention [ 13 , 14 ], short-term memory [ 14 – 16 ], and visual search [ 13 ]. However, these studies did not collect biometric measures of hydration status. Two additional studies conducted among children in Israel and Italy that assessed hydration status through urine osmolality found that dehydration was associated with decreased short-term memory [ 10 , 16 ].

Linking drinking water availability directly to cognitive skills among children in water-scarce areas would have important public health and policy implications. A deeper understanding of the relationship between hydration and cognition could provide significant and novel evidence for the importance of improving water access in schools. Here, we aim to address the gaps in existing literature by assessing the relationship between water consumption, hydration, and cognition in a setting where children do not commonly have water access during the school day.

We assessed the prevalence of dehydration among children attending schools in Mali, West Africa, and examined the effect of drinking supplementary water during the school day on hydration status and on cognitive test scores. Our hypothesis was that the majority of students would be dehydrated and that the provision of supplementary water would be associated with improved hydration and improved cognition. Methods included the piloting and refining of cognition measurements that had not been previously used in sub-Saharan African field settings. In addition, to our knowledge we collected one of the first sets of data indicating biometric levels of dehydration and reporting on the cognitive effects of dehydration in sub-Saharan Africa or elsewhere in the global South, where access to water is the poorest.

Materials and methods

We conducted a pilot study to investigate the impact of providing supplementary drinking water on the cognitive performance of pupils in water-scarce schools in rural Mali. The purpose of this study was to 1) pilot measures of short-term cognitive performance, 2) pilot field measures of hydration, 3) pilot data collection procedures for potential inclusion in a larger trial, 4) evaluate levels of dehydration among primary school students in water-scarce settings, and 5) test the association between drinking water and hydration on various measures of cognitive performance.

Data collection took place between January 7–10 and March 4–7, 2013 at two rural primary schools within 20 km of Sikasso town, Mali. Data collection at the second school was delayed due to armed conflict within the country. The maximum high temperature for data collection was 29°C in January and 40°C in March.

School eligibility, school selection, and participant selection

Schools were eligible for inclusion if they had no water point access within 0.5 kilometers, were within 1.5 hours drive from Sikasso town, and had at least 60 students in grades three through six. Two schools meeting eligibility requirements were purposively selected based on logistical considerations.

A total of 120 pupils in grades five (ages 9–13) and six (ages 10–16) were recruited. At each school, 30 pupils from each grade were randomly selected from school rosters using random number lists. In the event a pupil was absent or did not wish to participate, we continued to select pupils randomly from the class rosters until a sample size of 30 was reached for each grade.

Study design

We employed a crossover trial design in which each pupil in the study served as his or her own control. A crossover design was selected over a randomized controlled trial design due to the logistical challenge of randomizing water distribution within classrooms. Given the novel study procedures, crowded school setting, and limited timeframe, we were not certain that we could ensure water was not shared between pupils in intervention and control groups.

Hydration and cognition measurements were collected on two different days at each school. On one of the visit days we collected data without changing any conditions at the school (the control condition). On the other visit day we provided all pupils, regardless of participation in the study, with a 1.5 litre bottle of water in the morning, encouraged them to drink throughout the day, and refilled their bottle upon request (the water condition). We did not track the amount of water each pupil consumed. To account for confounding due to becoming familiar with the test (henceforth referred to as “practice effect”), the order of intervention days was counterbalanced between schools so that one school received water on the first day, while the other received water on the second day. Additionally, we included a separation of three days between visits.

To evaluate potential confounders or effect modifiers of hydration and cognition, participants were asked if they had anything to eat or drink that morning and reported drinking water availability at school. Staff members also made observations of drinking water availability at the school on the day of the visit. The majority of pupils went home at noon and returned for afternoon classes. We did not record lunch practices.

Measures of hydration

We collected three measures of hydration: urine specific gravity (U sg ), urine color (U col ), and self-reported thirst. Both U sg and U col are inexpensive measurements that can be easily conducted in the field with minimal training. They are strongly correlated with urine osmolality [ 17 , 18 ], a common measure of hydration in non-laboratory settings [ 10 , 11 , 16 ]. U sg measures urine density compared with water and was measured with ATAGO MASTER-URC/NM urine specific gravity analog refractometers (model 2793, ATAGO U.S.A. Inc., Bellevue, WA) [ 18 ]. The refractometers were calibrated using distilled water and were recalibrated at least every 15 readings, according to manufacturer instructions. U col was measured against a validated scale of eight colors [ 17 , 18 ]. Two trained enumerators independently evaluated each sample, and re-evaluated the sample together if their independent values differed; a third trained enumerator was consulted if no consensus was reached. Self-reported thirst [ 13 , 19 ] was collected on a five-point pictorial scale based on the Wong-Baker FACES pain rating scale [ 20 ]. For analysis, the least-thirsty image was assigned a value of 5 and values decreased to 1 as reported thirst increased.

Pupils provided urine samples between 8 and 9 am and again between 2–3 pm on each day of data collection. All urine analyses were conducted on the school grounds by trained study enumerators. Pupils self-reported thirst in the afternoon, after the completion of cognitive testing.

Measures of cognition

Cognition was measured using six tasks that assessed visual attention, visual memory, short-term memory, and visuomotor skills. These tests were taken from previous research on hydration and cognition that was conducted with children in Israel and the United Kingdom [ 10 , 13 , 14 ], piloted in Mali, and adapted to the Malian context.

Letter cancellation

This test assesses visual attention . Pupils were given a grid containing target letters randomly dispersed among non-target letters and were given one minute to cross out as many target letters as possible. Scores were calculated by subtracting the number of non-target letters identified from the number of target letters identified; the maximum test score was 38.

Direct image difference

This test assesses visual attention . Two nearly identical pictures were presented side-by-side. Pupils were given one minute to circle differences between the two images. Scores were calculated by subtracting the number of incorrect differences identified from the number of correct differences identified; the maximum test score was 9.

Indirect image difference

This test assesses visual memory . Two nearly identical pictures were presented in sequence. Pupils were given ten seconds to study the first image. They were then briefly presented with a blank page, followed by a second image, and given one minute to circle the differences between the two images on the second image, without returning to the first. Scores were calculated by subtracting the number of incorrect differences identified from the number of correct differences identified; the maximum test score was 9.

Forward digit recall

This test assesses short-term memory . Twelve sequences of numbers two to seven digits in length were read aloud to pupils at a rate of one number per second. Pupils were asked to write down the sequence in order after the sequence was read aloud. Two scores were derived from this test: the total number of correctly recalled sequences (maximum score of 12) and the maximum digit span of the correctly recalled sequence (maximum score of 7).

Reverse digit recall

This test assesses short-term memory . Ten sequences of numbers two to five digits in length were read aloud to pupils at a rate of one number per second. Pupils were asked to write down the sequence in reverse order after the sequence was read aloud. Two scores were derived from this test: the total number of correctly recalled sequences (maximum score of 10) and the maximum digit span of the correctly recalled sequences (maximum score of 5).

Line tracing task

This test assesses visuomotor skills . Pupils were presented with two curved parallel lines. They were given fifteen seconds to draw a line between them as quickly as possible while attempting not to touch the printed lines. Scores were calculated by subtracting the number of times the pupil’s line touched the side from the total length of the line in centimeters; the maximum test score was 29.

All cognitive tests were paper-based and administered by trained study staff in a group setting within the school classrooms. Testing sessions were standardized using written scripts. Staff introduced each test with a scripted explanation and an example, with no breaks between tests. Testing sessions lasted a total of 60–75 minutes and began at 3:00 pm in the afternoon of each visit. Each pupil in the study completed the testing session twice, once on the control condition day and once on the supplementary water condition day. Four parallel versions of each test were developed so that individual pupils did not receive the same test twice and pupils sitting next to each other did not receive the same test. All four test versions were distributed at each testing session. Tests were independently graded by two different staff members using fixed criteria. Grading criteria also provided guidelines to indicate whether or not pupils understood the tasks according to instruction. Tests with conflicting scores were examined by the study coordinator, who decided the final score for the task.

Data analysis

Data were entered into MS Excel and analyzed using STATA 13 SE. We tested both the impact of treatment condition (whether student was provided water or not during the day) and hydration status on change in test score. U sg was used to test the impact of hydration on change in test score because it was the only of our three hydration measures based on biomarkers, and is the most accurate of those three measures of hydration status [ 21 ]. A higher U sg indicates increased dehydration. Pupils were classified as dehydrated if they had a U sg of 1.020 or higher, which is equal to the dehydration threshold of urine osmology>800 mOsmol kg-1 H 2 O that has been used in previous studies of dehydration among children [ 10 , 11 , 16 ]. A total of eight scores for the six cognitive tests were calculated according to grading criteria. Scores were coded such that higher test scores on all cognitive tests represented better performance.

Univariable analysis

As proof of concept of the effect of water provision on hydration, we evaluated univariable differences in morning and afternoon hydration, U sg , and U col by treatment group using McNemar’s test statistic (binary variables) and paired sample t-tests (continuous variables). To evaluate the correlation between U sg , U col , and self-reported thirst, as well as the correlation between each of the cognitive test scores, pairwise tests of correlations between cognitive test scores were conducted using the pwcorr command. Lastly, to measure the presence of a “practice effect,” paired sample t-tests were used to assess differences in cognitive test scores between school visits.

Multivariable analysis

We examined the association between the provision of supplementary drinking water (treatment) and cognitive test scores as well as the association between pupil hydration (regardless of treatment) and cognitive test scores. These associations were assessed using separate mixed-effects linear regression models, where each cognitive test was the outcome, while treatment condition or hydration status, respectively, was the predictor covariate. Models included a random intercept at the pupil level to account for pupils acting as their own control. Unstandardized Beta coefficients are presented.

All models adjusted for multiple comparisons using the Bonferroni correction; as such, associations were considered significant if they had a p -value <0.006, the alpha necessary to reach 95% significance with eight hypotheses. Models were assessed for interaction and confounding with the following variables chosen a priori : pupil sex, pupil grade, reported drinking in the morning, reported eating in the morning, reported thirst, and morning hydration.

Interaction was assessed by running models of each cognitive test outcome with each predictor variable, potential interaction covariate, and an interaction term for the predictor and covariate (e.g. treatment*sex). Some variables initially indicated interaction at p <0.05. However, after adjusting for multiple comparisons using the Bonferroni correction, the only effect modifier to retain significance was pupil sex, which modified the relationship between afternoon dehydration and forward number recall- maximum digit span test score. Stratified results from this model are presented. All other associations were then tested for confounding; covariates significantly associated with the predictor variable as well as the outcome variable in independently run fixed-effect models were considered to be confounding variables. At p = 0.006, grade confounded the association between treatment and direct image difference & indirect image difference test scores, so was included as a control variable in these models. All models controlled for the visit day in order to account for a “practice effect” on cognitive tests.

We compared models from all pupils to models that excluded scores from pupils who did not complete cognitive tests according to instruction. There were no significant differences between model results, thus, we present the former results in order to maximize sample size. Only students with complete data for all measures of interest were included in analysis. We dropped 13 pupils due to absence on the second day of data collection, not being able to provide a urine sample, or inability to match pupils test scores and hydration measures due to improper identification procedures.

This study was approved by Emory University’s Institutional Review Board (IRB00062354), the Mali Ministry of Education, and the National Technical and Scientific Research Center ( Centre National de la Recherche Scientifique et Technique ) in Mali (001/2013-MESRS/CNRST). All three institutions approved consent in loco parentis (in the place of parents) due to the logistical challenges of finding and contacting parents in their homes, risk of lost wages to parents if they were summoned to school, and low levels of literacy making letters unfeasible. Permission for study activities and approval of a waiver of parental consent was also obtained from the Centres d’Animation Pédagogique (Center for Pedagogical Activity) and Académie d’Enseignement (Academy of Education) in Sikasso, both local government representatives responsible for education in the area where the study was conducted. Prior to commencing study activities at each school, we obtained consent in loco parentis from the school director and the Comité de Gestion Scolaire (school management committee), the organization empowered to oversee management and activities at the school, on behalf of the community that school serves. Pupils who were selected for the study provided informed verbal assent in a private setting prior to the start of data collection activities.

Study population

Data were collected from 120 pupils in two schools; of these, 107 (89.2%) pupils had complete data and were included in analysis. The sample was initially comparable in terms of sex, grade, and school. After removing pupils with incomplete data (n = 13), the final sample included 46 (43.0%) girls, 61 boys (57.0%); 58 (54.2%) pupils from grade five, 49 (45.8%) pupils from grade six; 47 (43.9%) from School 1, and 60 (56.1%) from School 2. The mean (sd) age was 11.6 (1.0) years in School 1 and 12.1 (1.7) years in School 2.

Univariable estimates of association with hydration

Only 3% of pupils were classified as dehydrated in the morning according to U sg (U sg >1.019), regardless of visit day or study condition. The difference between water and control condition mean morning U sg or U col was not statistically significant, and we found no difference in the prevalence of dehydration prior to distribution of water.

Pupils became more dehydrated throughout the school day under both study conditions. There was no significant difference in U col , self-reported thirst, or the prevalence of pupils classified as dehydrated in the afternoon under the water condition compared to the control condition. However, mean afternoon U sg was significantly higher under the control condition compared to the water condition ( Table 1 ). U sg and U col were strongly correlated both in the morning (r = 0.777, p <0.001) and afternoon (r = 0.734, p <0.001). Self-reported thirst, which was only measured in the afternoon, was not significantly correlated with either afternoon U sg (r = 0.089, p = 0.20) or afternoon U col (r = -0.003, p = 0.97).

* p -value based on McNemar’s test statistic for binary variables and paired sample t-tests for continuous variables

† Pupils with a U sg >1.019 classified as mildly dehydrated

Bold values indicate a significant association at α = 0.05

Univariable estimates of association with cognition

Results from pairwise tests of correlations between cognitive test scores and results from the paired t-tests of the association between test score and visit day are shown in Table 2 . Most tasks were significantly correlated with at least one other task included in the battery of cognitive tests. Students achieved significantly higher scores on the second visit compared to the first visit for six of the eight cognitive tests, regardless of treatment condition.

* p -value based on paired t-tests

Target skills assed by test:

1 visual attention

2 visual memory

3 short-term memory

4 visuomotor skills

Multivariable estimates of association between cognitive test scores and treatment condition

In adjusted models, the provision of supplementary drinking water was significantly associated with two cognitive tests: reverse number recall (total) and line trace. Under the water condition, pupils performed better on the reverse number recall test. However, pupils had lower scores on the line trace test under the water condition ( Table 3 ).

*Pupils with a U SG >1.019 classified as dehydrated

Bold values indicate a significant association at α = 0.006, the level of 95% significance after correcting for multiple comparisons

Models include a random intercept at the pupil level to account for clustering

Multivariable estimates of association between cognitive tests scores and hydration status

We examined the impact of hydration on cognitive test performance, regardless of treatment condition. Neither hydration status, where a U sg greater than 1.019 indicated dehydration, nor U sg were significantly associated with any cognitive test score ( Table 3 ). The test for interaction indicated that pupil sex significantly modified the association between forward number recall (maximum) and afternoon dehydration. When stratified by sex, males performed worse when dehydrated (β = -0.14; 95% CI -0.54, 0.27; p = 0.501) and females performed better when dehydrated (β = 1.10; 95% CI 0.31, 1.89; p = 0.006); only the association between hydration and forward number recall among female pupils approached statistical significance.

We conducted a cross-over trial as part of a pilot study to examine the associations between water consumption, hydration, and cognition among pupils attending water-scarce schools. We successfully adapted measures of cognitive performance that could be completed by children in rural Malian schools and tested the feasibility of field hydration measures and data collection procedures within schools in Sub-Saharan Africa. Results demonstrated that supplementary water provision within a school setting significantly decreased U sg , even within a short time period. However, we found no effect of the impact of supplementary water provision on cognitive test scores.

This research refined a battery of cognitive tests for use with children in Mali which can be adapted to other developing settings. Research conducted in the U.K. concluded that their cognitive test of visual memory was too easy for the target population, indicated by many children achieving the maximum score on the test, and thus modifying study results [ 13 ]. Our results show that the percentage of children achieving the maximum score or the minimum score on any of the cognitive tests ranged from 0.5%-15.4% and 0.5–4.2%, respectively, indicating that the cognitive tests adapted for this trial were neither too difficult nor too hard. However, results from our pairwise tests of correlation indicate that the two tests measuring visual attention (letter cancellation and direct image difference) were not significantly correlated, suggesting that further adaptation may be needed on these tests to measure this target skill. Furthermore, while scores for each of the four tests measuring short-term memory were significantly associated with at least one other score in the suite of tests measuring that domain, they were very similar tests in that they all incorporated number recalls. Thus, correlation does not necessarily indicate that they were in fact measuring the cognitive skill they were intended to measure.

This is one of the first studies to employ existing field methodology to collect urine samples and measure dehydration among school children in low-resource school settings. Results from this pilot study were further refined in a subsequent trial in Zambia [ 22 ]. Prior research on dehydration among schoolchildren has relied predominantly on self-reported thirst as their measure for dehydration. Although evidence- particularly among healthy individuals- is limited, research has concluded that one’s thirst response is not an accurate measure of hydration [ 23 , 24 ]. We found no research investigating this association among children. Our results demonstrated no significant difference between self-reported thirst among pupils under the water condition compared to the control condition, even though the measurements of U sg indicated that pupils under the water condition had significantly higher levels of hydration than pupils under the control condition. Additionally, self-reported thirst and the biometric measurement of U sg were not significantly correlated. These findings support previous literature concluding that self-reported thirst is not an accurate measure of hydration. Given our findings, future research should consider utilizing only measurements that provide biometric evidence of dehydration. Data also revealed that U col , although strongly correlated with U sg , did not capture a significant difference in afternoon hydration between water and control conditions. We believe this may have been due to the subjective nature of matching urine color to the color chart. The use of refractometers to measure U sg required less training and took less time than measuring U col , and thus is recommended for future studies investigating dehydration levels of subjects in low-resource settings.

Our finding that only 2.8% of pupils were dehydrated in the morning stands in stark contrast to previous research which reported that 84% of Italian school children [ 16 ], 68% of Israeli school children [ 11 ], and 43% of Zambian schoolchildren [ 22 ] were dehydrated at the beginning of the school day. While this result was initially surprising, it may be partly explained by evolutionary mechanisms. In their research, Bar-David reported that among their sample of Israeli schoolchildren, Bedouin children, who originate from a population that has lived in the desert for many generations, had the lowest mean urine osmolality (the lowest prevalence of dehydration), possibly because their bodies adapted over time to have a lower threshold of thirst [ 10 , 11 ]. Thus, Malian children, who reside in hot, arid, and water-scarce environments, may have also adapted a greater resistance to dehydration, leading to a lower prevalence of dehydration at the beginning of the school day. Extremely low levels of morning dehydration may also be partly explained by the fact that a vast majority of students (93%) reported drinking something in the morning before going to school. We do not believe that pupils intentionally consumed more water than usual in preparation for participation in the research. Neither school officials nor pupils were aware of the study topic, activities, or pupil selection prior to the first day of the study. Thus, participants would not have had the foreknowledge to alter their normal drinking behaviors. Although school officials and pupils were aware of the date of the second visit, given that no significant differences in the prevalence of dehydration or U sg were observed between the first and second visits, it is unlikely that students changed their drinking practices for the second day.

Under both treatment conditions, dehydration increased throughout the day. Pupils had significantly lower U sg in the afternoon under the supplementary water condition than under the control condition, demonstrating the “proof of principle” that supplementary water provision improves hydration. However, there was no significant difference in the prevalence of afternoon dehydration among pupils in the water group compared to pupils in the control group. Nonetheless, when the significant impact of water consumption on increasing U sg is considered in light of findings of the relationship between drinking water and cognition from other contexts [ 13 – 16 ], there is evidence that providing drinking water at school may create a positive impact on pupil learning.

We found some evidence that supplementary water provision was associated with higher scores on cognitive tests, but few results were significant. These results are consistient with those from our follow-up trial among primary school children in Zambia [ 22 ]. Treatment was significantly associated with higher scores on the letter cancellation task, a result supported by previous literature that also found a positive relationship between provision of drinking water and performance on visual attention tasks [ 14 , 22 ]. While previous studies have reported no significant association between water provision and visuomotor skills [ 13 , 14 ], we found that scores on the line trace test were significantly, but negatively associated with supplementary water provision. Although this result was unexpected, it may be largely explained by a practice effect, in which pupils performed significantly better the second time they took the test, regardless of treatment condition. Although pupils took a different version of the test on each day, a practice effect was evident, as test scores significantly improved when pupils performed each task the second time. One possible reason for this difference could be that pupils in Mali are not accustomed to the types of activities performed during the tests, which were adapted from tests used in Western settings. Although the distribution of test scores and the correlation of tests measuring the same domain do indicate that the tests were suitably adapted to the context, the novelty of the tests may have caused a much lower baseline score at the first testing session. Pupils may need to practice completing the tasks several times in order to fully understand the tests before their scores are measured.

Lastly, evidence on the degree and duration of dehydration necessary to impact cognitive performance is limited. It is possible that the lack of significant improvements in cognitive performance following treatment is because one school day of supplementary water provision is not sufficient to reverse the impacts of chronic dehydration and impart cognitive benefits on schoolchildren; perhaps more long term water consumption is necessary for these benefits to be measurably improved [ 22 ]. Further, although the U sg data provide evidence that pupils drank under the treatment condition, we did not measure the volume of water consumed by subjects. Measuring the volume of water consumed by subjects and including a dose-response measure in the analysis could contribute to the discourse on how much water consumption is needed to improve hydration, and how much hydration is needed to improve cognition.

Limitations

There are several limitations to the current research. First and most crucial was the impact of the practice effect, in which pupils performed significantly better on cognitive testing during the second visit, regardless of treatment condition. Approaches to limit or account for the practice effect on cognitive testing in primary school populations residing in settings where this type of testing is uncommon requires additional attention; future research should focus on alternative trial designs to minimize this impact. Additionally, the fixed test order could have led to a learning effect across tests, where certain tests- conceivably later on in the series- revealed a more significant association due students becoming more comfortable with testing in general, rather than due to the skill tested. Students in both the intervention and control would have had the same learning effect, which would bias our results to the null, but there is no way to control for this within the individual models. However, we observed no trend where students performed differently on tests administered in the end of the suite on either testing day. Further, we reviewed the estimates of effect and do not find any effect modification. Second, because this was a pilot study, the sample was limited to 120 pupils in two schools. As such, the study may not have been sufficiently powered to detect significant but less strong impacts of supplementary water provision or hydration status on cognitive performance. Low levels of dehydration across study groups may have also further limited our ability to detect an impact. Third, we conducted an intention-to-treat analysis and did not measure or control for the volume of water consumed by the participants in the treatment group. We did not measure whether pupils in the control group consumed water brought from home, and we could not ethically restrict them from drinking water. We also did not record lunch practices among students, and cannot guarantee that children did not consume water when they went home for lunch. As such, we cannot unequivocally state that the intervention and control groups were separated by water consumption, or lack thereof. However, afternoon U sg was collected regardless of treatment condition, and results validate the degree of water consumption under treatment. Additionally, lunch practices among individual students would likely be similar across days, thus the influence of lunch practices would be consistent across test conditions since pupils act as their own controls. Fourth, due to external events, data collection at the second school was delayed for two months and occurred during a warmer period. The higher temperatures during the second data collection period may have impacted study results. Evidence suggests that exposure to heat may independently impact cognitive functions, however this research has not been conducted among children [ 25 – 27 ]. Although significantly more pupils in the second school were dehydrated in the afternoon compared to pupils in the first school, due to the crossover design, it is not possible to quantify the effect that temperature may have had on study outcomes. Last, the methodology, including the duration of tests, were adapted from cognitive tests previously used among primary school children [ 13 , 14 , 28 ], but the total testing time was longer than in previous studies due to the novelty of the tests in the population and our emphasis on explanation and examples. However, because there was no significant trend in scores across the testing suite, there is no evidence that performance worsened due to fatigue among students.

We suggest a two-step approach for collecting further evidence on hydration and cognition among pupils in water-scare schools. First, we recommend implementing a second trial with cognitive testing methodology that addresses the challenges of the practice effect in order to increase the evidence base on the link between hydration and cognition among schoolchildren in water scare areas. Once the link between improved hydration and cognition among schoolchildren has been established under experimental conditions, we recommend carrying out cross-sectional hydration testing in a larger sample of schools. Considering the apparent invalidity of self-reported thirst and the subjective nature of urine color evaluation, we recommend the use of urine specific gravity or another objective biometric measure for hydration testing. Given the evidence previously established, hydration in this case would serve as an easily quantified and measured proxy for pupil attention, memory, and concentration. Findings from this investigation could provide evidence of the benefit of drinking water access, and specifically on the construction of water points on school grounds, for pupils’ educational attainment.

Conclusions

This study represents novel research across multiple scientific disciplines and development sectors, and is an important step in developing clear and direct linkages between provision of WASH in schools and learning. Results demonstrated the proof of principle that increased water access improves hydration. Although we found no evidence for our hypothesis that improvements in hydration status leads to improvements in cognitive performance among pupils in water scare schools, results may have been masked by a strong practice effect, and the power to detect significant differences was limited. We demonstrated the feasibility of collecting biometric measurements of hydration status and testing cognitive abilities in resource-poor settings. Findings from this research and subsequent studies of hydration and cognition have broad significance for advocacy for international development and health sectors for increased attention to insufficient access to water supply for school children.

Supporting information

Acknowledgments.

This study was funded by the Emory University Research Committee. Additional in-kind support was given by Save the Children and Dubai Cares. We would like to thank Sarah Porter for assistance with development of the study, as well as Birama Diallo, Seriba Diallo, Makan Keita, Sadio Sangaré, and Mariam Traoré of Save the Children and Jérémie Toubkiss of UNICEF for their support.

Funding Statement

Funding was provided by the Emory University Research Committee ( http://www.urc.emory.edu/grants/urc/index.html ). MCF received funding (grant number N/A). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Data Availability