Body in the water

What role does water play in the human body?

The water you consume through the food you eat and what you drink follows a very precise route to arrive in your cells. After passing through the stomach, water enters the small intestine, where it is largely absorbed in the first sections, the duodenum and the jujenum. The rest passes into the colon, where it crosses the intestinal mucous membrane into the bloodstream, and then into the interstitial tissues that makeup the framework of every organ, to finally arrive in cells.

Water in the cells

At the most foundational level, water is necessary for all cells—human or otherwise—to carry out the chemical reactions that allow them to live. Water enables hydrolysis, a vital process by which cells breakdown what we eat (lipids, proteins, and carbohydrates) and create energy. But if we go “up” a level or two in size and scale, the role of water in the human body becomes more readily comprehensible, and relatable.

Water on a bigger scale

The body needs water to perform all of the following functions: regulating body temperature, lubricating joints, moistening tissues in the mouth, eyes, and nose, helping to dissolve nutrients and make them accessible in the bloodstream, carrying nutrients and oxygen to cells, and for flushing out waste products. In other words, nearly everything that the body does requires water.

Sources: Nestlé Waters – 5 Water Functions in Human Body / Nestlé Waters – Water in Your Body

RehydrationThe human body and water

  • The Story of POCARI SWEAT
  • The rehydration drink that is now a global brand
  • Changes in body fluid volume and its composition during heavy sweating and the effect of fluid and electrolyte replacement
  • Sports medicine and biochemistry related to two sports drinks
  • The effect of ingestion of an electrolyte-sugar drink on recovery from dehydration
  • Changes in blood volume following administration of oral rehydration solutions
  • Effects of hydration on fluid balance and lower-extremity blood viscosity during long airplane flights
  • Changes in plasma volume and blood viscosity during a 4-hour period sitting in a dry environment: The effects of prehydration
  • Rehydration after bathing: Comparison between a carbohydrate-electrolyte beverage and water
  • Effects of a carbohydrate-electrolyte beverage on blood viscosity after dehydration in healthy adults
  • Effect of prehydration on nasal mucociliary clearance in low relative humidity
  • Enhanced renal Na+ reabsorption by carbohydrates in beverages during restitution from thermal and exercise-induced dehydration in men
  • What are electrolytes (ions)?
  • The human body and water
  • When the body lacks water

Water: It’s More Than Just a Drink

Last Updated: Mar 1, 2019


Eight glasses of water a day, right? Maybe not. For some time now, experts have told us to drink eight 8-ounce glasses of water each day. Because we’ve heard this mantra for so long, it’s difficult to imagine that it wouldn’t be the truth. There isn’t any evidence for it, however, concluded scientific reviews in 20021 and 2008.2 What’s more, in 2004 the Institute for Medicine (IOM) issued new fluid guidelines stating that average healthy Americans should let thirst be their guide and that even caffeinated beverages like cola, tea and coffee count toward our fluid requirements.

On this page:

Lastly, if you would like to learn more about yourself and how you can best reach your own nutritional and fitness goals, we encourage you to take a look at the following home health testing guides and resources:

That’s not to say that water is not important. In fact, at least 50% of your body is water. Take a look at what it does for you.

Water in the Body

Water has the following functions within the human body.

  • Transports nutrients and other compounds. As a major component of the blood, water helps move glucose, water-soluble vitamins, minerals, other nutrients and some medications throughout your body.
  • Cools you. When you become too hot, your blood vessels dilate and you start sweating. The sweat evaporating on your skin is cooling. Water also has a high heat capacity. This means that a lot of energy is needed to increase its temperature. Since the body contains more water than anything else, it takes quite a significant amount of heat to raise your body temperature.
  • Protects and lubricates. It would be hard to swallow a peanut butter sandwich or practically any food without saliva, wouldn’t it? Fortunately, our salivary glands produce ample saliva, which is largely water. Tears lubricate and clean the eyes, and synovial fluid lubricates your joints. Cerebrospinal fluid protects your brain and spine from trauma. Similarly, amniotic fluid surrounds and shields the fetus. Fluids throughout your body protect and lubricate your organs and tissues.
  • Participates in metabolism. Most chemical reactions in your body use water in at least one of three ways: a solvent, a reactant or a product of the chemical reaction. Water produced in chemical reactions is called metabolic water, and your body uses it in the same ways it uses the water you drink.

Even though the myth of drinking eight glasses of water a day may not be true, water is still an essential ingredient in your body’s system.

Water in the Diet

If you are the typical American adult, you consume about 20 to 25% of your daily water from solid foods. Fruits, vegetables, cooked grains and even meats and cheese provide water. The rest of your water intake comes from beverages of all types.

Water Content of Selected Foods and Beverages (food and its percentage of water by weight):

  • Apple: 85%
  • Milk, skim: 91%
  • Banana: 75%
  • Chicken breast, roasted, skinless: 65%
  • Broccoli, cooked: 89%
  • Cheddar cheese: 37%

Source: USDA Nutrient Data Lab3

How much fluid do you really need?

The IOM report does not specify water requirements. Rather it includes guidelines for total fluid intake. From both food and beverages, women should consume, on average, 91 ounces of total water, and men should have 125 ounces of total water daily. This should cover your fluid losses in urine and feces, and the normal, but continual losses from the lungs and skin. The water loss from the skin and the respiratory tract is referred to as insensible water loss. If you are sick, you may lose additional water from nasal secretions, through vomiting or diarrhea or from sweating with a fever. Thus, you’ll need to drink additional beverages.

How should you measure your fluid intake?

There is usually no reason to measure your water intake or impose a water requirement on yourself. Healthy people will meet their fluid needs by paying attention to their thirst. If you have heard and believed that thirst is a poor indicator of hydration status, you have fallen prey to another myth. Though we often hear such things as, “by the time you’re thirsty, you are already dehydrated,” the truth is that experts define dehydration when the concentration of blood has increased by at least 5%, but thirst begins much sooner than that, usually before the concentration of blood rises 2%. Thirst may not indicate hydration status, however, for individuals with medical conditions requiring fluid control, individuals taking some medications, athletes or those involved in other strenuous activities, or people living in especially hot climates.

What are some liquid sources of water?

Athletes and heavy sweaters may benefit from sports drinks. They are ideal for individuals who are very active for at least 60 minutes. They contain fluid and electrolytes lost in sweat, as well as carbohydrates to refuel and prevent fatigue. For casual exercisers who sweat little, sports drinks likely offer little more than water and extra calories. Added vitamins in sports drinks are unnecessary because we do not lose vitamins in sweat. Sodas, sweet tea and fancy coffee drinks also provide you with necessary water, but they give you plenty of unnecessary added sugars and calories, so have them only rarely.

To keep your body hydrated, you can do more than just drink water. Many healthy foods contain water, as well as some of the other liquids you consume, such as milk. Eat and drink a variety of foods and liquids to make sure your fluid intake is where it should be.

Water and Electrolytes: A Critical Balance

Electrolytes are substances that, when dissolved in water, dissociate into positively and negatively charged ions. This makes them capable of carrying an electrical current. For example, when you dissolve salt (sodium chloride) in water, sodium and chloride separate. Sodium provides a positive charge and chloride brings a negative charge. Electrolytes help maintain fluid balance because they draw water to them. Through osmosis, water will cross cell membranes to make the concentration of dissolved particles the same on both sides. The major electrolytes are sodium, potassium, chloride and phosphorus.


This is the major positively charged electrolyte in the extracellular fluid (fluid outside the cells).

  • Functions: Sodium helps regulate blood pressure; assists with acid-base balance; aids in muscle contraction; assists with the transmission of nerve signals; and participates in the active transport of glucose and some other nutrients.
  • Recommended intakes of sodium: Our actual daily requirement for sodium is very small, just a few hundred milligrams. It would be hard, perhaps impossible, to eat so little sodium and still maintain a diet adequate in other nutrients. For this reason, the IOM set the Adequate Intake (AI) at 1500 mg. The Tolerable Upper Intake Level (UL) is at 2300 mg. The 2010 Dietary Guidelines for Americans is more strict and recommends a daily limit of 1500 mg of sodium for anyone age 51 years or older, all African Americans, and all people with high blood pressure, diabetes or chronic kidney disease. This includes almost half of the population – including children! The rest of the population is advised to limit sodium consumption to 2300 mg/day. Most Americans consume significantly more sodium than health experts consider safe. According to the Centers for Disease Control and Prevention (CDC), the average daily sodium intake for Americans over the age of two is more than 3400 mg.4
  • Sources of sodium: Though it is not the saltiest food per serving, bread is the greatest contributor of sodium to the American diet because it is so frequently consumed.5 Approximately 10% of our sodium intake is from sodium that occurs naturally in our food. Three-quarters of our intake comes from processed foods and restaurant foods. The rest comes from what we add in cooking or at the table. Thus, the most important steps to reducing sodium intake are to eat few highly processed foods and to prepare many of our meals from scratch.
  • When you get too much or too little sodium: High sodium diets are linked to high blood pressure, bone loss and kidney stones. Low sodium intakes relative to sodium losses in sweat can cause overhydration, which can be deadly.


This is the major positively charged electrolyte in the intracellular fluid (fluid within the cells).

  • Functions: Potassium assists with managing blood pressure by blunting the effects of excess sodium; aids in muscle contraction; and assists in nerve transmission.
  • Recommended intakes of potassium: The AI for potassium for adults is 4700 mg per day. For children, the AI ranges between 3000 and 4700 mg, depending on age and gender. Unfortunately, less than 3% of Americans meet the AI for potassium.6
  • Sources of potassium: The most notable sources of potassium are fruits, vegetables and dairy, though potassium is present in all food groups. High-potassium foods include white and sweet potatoes, beans, leafy greens, tomatoes, oranges, halibut and clams.
  • When you get too much or too little potassium: A severe dietary imbalance of potassium is rare in healthy people. Individuals with healthy kidneys excrete excess potassium readily. If people take large doses in the form of supplements or if they have impaired kidney function, potassium can build up in the blood and alter the electrical rhythm of the heart causing heart attack and death. Because potassium helps to balance sodium, low potassium intakes are linked to high blood pressure, especially when sodium intake is excessive.


This is the major negatively charged electrolyte in the body.

  • Functions: Chloride is used to form hydrochloric acid (HCl) secreted into the stomach; aids in the immune function; and assists in nerve transmission.
  • Recommended intakes of chloride: For men and women aged 19-50 years, the AI for chloride is 2300 mg.
  • Sources of chloride: Chloride is usually found as sodium chloride, common table salt.
  • When you get too much or too little chloride: Since chloride is usually consumed as table salt, there are no known toxicity symptoms for chloride alone. Deficiencies of chloride do not occur from lack of intake, but rather from severe vomiting or dehydration.


This is the major negatively charged electrolyte in the intracellular fluid, usually combined with oxygen in the body to form phosphate.

  • Functions: Phosphorus makes up part of DNA, RNA, cell membranes and the mineral complex in the bone; assists in providing the body with energy, as a component of ATP (adenosine triphosphate); and helps regulate biochemical reactions by activating or deactivating various enzymes.
  • Recommended intakes of phosphorus: The Recommended Dietary Allowance (RDA) for adults is 700 mg/day. For adolescents and teens, the RDA is 1250 mg/day.
  • Sources of phosphorus: Where there is protein, there is usually phosphorus. Some of the best sources of this mineral are meats, eggs and dairy. Highly processed foods, especially sodas and processed meats, also provide ample phosphorous to the diet.
  • When you get too much or too little phosphorus: Phosphorus is ubiquitous in the diet, so dietary deficiencies are extremely rare. Low blood phosphorous levels may come from parathyroid disorders, vitamin D deficiency or overuse of phosphate binding antacids. In the short-term, low phosphorous levels can cause muscle weakness. Weakening of the bones occurs when low phosphorous levels occur long term. High phosphorous levels in the blood can occur when individuals take excessive vitamin D supplements or phosphorous-containing laxatives. Individuals with kidney disease may also experience high phosphorous levels. Very high blood levels of phosphorous can cause muscle spasms and convulsions. Knowing whether you have too much or too little vitamin D in this case can be very helpful; a vitamin D home test allows you to find out conveniently from home.

Electrolytes are no less important than fluid for maintaining proper hydration status. And as you can see, each of the above minerals plays multiple roles in the body – from bone density to immune function, muscle contraction and nerve transmission. Eating a balanced diet with an abundance of fresh fruits and vegetables will help assure the proper intake of these minerals.

Maintain Safe Hydration Levels

You can see how intricately tied water and electrolytes are in the body. A problem with one easily leads to a problem with the other. It might be hard to imagine that water, something so pure, so critical for life can be toxic.

  • Overhydration: Overhydration or water intoxication can occur when athletes replace excessive sweat losses with plain water. Remember that sweating causes loss of water and electrolytes. When water only is replaced, the concentration of sodium in the blood becomes too low, a condition called hyponatremia. Severe hyponatremia is lethal. It can also occur when large quantities of water are consumed so rapidly that the kidneys cannot excrete the excess.
  • Dehydration: Dehydration occurs when too much fluid is lost from the body through sweating, vomiting or diarrhea. The treatment for mild dehydration is water or water and salts. Severe dehydration requires medical attention with intravenous fluids and careful monitoring of electrolytes.

Water is an essential part of the human body. Make sure you drink enough fluids and eat foods that contain water. You may not be able to measure the exact amount of ounces you consume during a day, but if you eat healthy foods, and drink fluids that contain more water than sugars or additional calories, you should maintain safe hydration levels.



  1. Valtin Heinz. “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 283: R993-R1004, 2002. ↩

  2. Kolso J, Jeckel K, Wildman EC. Water, Hydration and Health: What Dietetics Practitioners Need to Know. SCAN’s Pulse Winter 2012 Vol.31, No. 1. ↩

  3. USDA Nutrient Data Lab Accessed March 9, 2012. ↩

  4. ↩

  5. Dietary Guidelines for Americans, 2010. U.S. Department of Agricultural, U.S. Department of Health and Human Services, 2010Pg 22 ↩

  6. Fulgoni VL III, Keast DR, Bailey RL, Dwyer J. Foods, fortificants, and supplements: where do Americans get their nutrients? J Nutr 2011;141:1847-54. ↩

5 Functions of Water in the Human Body

Water. We drink it, we bathe in it, and we swim in it but what roles does it play in our body? Here are just 5 ways water keeps our body healthy and in an optimum state to function effectively.

  1. Hydration

Water helps to keep dehydration at bay and prevents nasty symptoms such as headaches, fatigue and dry skin. Most people take on board enough water throughout the day by drinking when they feel thirsty and drinking with their meals. But there are some groups of individuals which may need a little more encouragement, including the elderly and the young. Keeping yourself hydrated doesn’t mean you should only drink plain water. Instead, drinks including squash, tea and coffee all count as do watery fruits and vegetables such as strawberries and cucumber.

  1. Protection

As well as keeping us hydrated, water helps to keep our tissues moist. Our eyes, nose and mouth can be prevented from feeling dry by keeping the body hydrated through adequate water intake. Other areas of the body which can benefit from this include the brain, blood and bones. Furthermore, our joints such as our knees, ankles and elbows are kept lubricated and cushioned by water, and it also keeps our spinal cord protected.

  1. Waste Removal

The obvious answer for this is, of course, the process of urination and defecation. However, adequate water intake also ensures waste is removed through sweating. The liver, kidneys and intestines also require water to flush waste from them. You may be able to prevent constipation (this is not scientifically proven) by drinking lots of water as this helps to soften your stools and facilitates the movement of food through the intestinal tract.

  1. Digestion

The first process of digestion is chewing – a process which involves saliva. The basis of saliva is water and helps to soften our food ready to be swallowed alongside enzymes which dissolve minerals and nutrients. Water helps the body to digest soluble fibre. Soluble fibre includes pectin’s and beta glucans – found in oats and fruit. In the presence of water, this fibre dissolves easily and aids your digestion by helping to form soft stools which are easy to pass.

  1. Regulation of Body Temperature

The intake of water helps to regulate our body temperature. When it is hot outside, we sweat more and so lose more water. Therefore, keeping our body temperature constant.

Generally, you should aim to drink around 1.5 litres of water per day, but we are all different. You know yourself better than anyone and will know if you feel thirsty or dehydrated. Remember, if you participate in vigorous exercise, have a fever or an illness such as vomiting and diarrhoea, you will need to replace the lost fluids. Likewise, if you are pregnant or nursing you may want to speak to your GP about increasing your fluid intake particularly if you are breastfeeding because your body will use more water than normal.

Americans seem to carry bottled water everywhere they go these days. In fact, it has become the second most popular drink (behind soft drinks). But water lovers got a jolt recently when we heard that a new report had found that the benefits of drinking water may have been oversold. Apparently, the old suggestion to drink eight glasses a day was nothing more than a guideline, not based on scientific evidence.

Video Transcript

MICHAEL SMITH: It sounds too good to be true. Just drinking more water can help you lose weight. But that’s what researchers found. Drinking as little as 1% more water means you’ll eat fewer calories. You’ll also benefit from a drop in saturated fat, sugar, sodium, and cholesterol. One extra cup of H2O in a day will save you 68 calories. And you don’t have to do this every day to get the savings. Drink three extra cups, and you’ll cut your calorie intake by 205. To put it in perspective, that’s as many calories as you’d burn if you walked two and a half miles. Now, you can’t just lie around on the couch all day and chug a gallon of water instead. You still need to keep up those healthy habits. And no word on what happens if you drink more than three cups, except for spending a lot of time in the bathroom. And this doesn’t mean you can eat more, just that you’re more likely to eat less. But that walk to the water cooler gets you a lot further than you thought. For WebMD, I’m Dr. Michael Smith.

But don’t put your water bottle or glass down just yet. While we may not need eight glasses, there are plenty of reasons to drink water. In fact, drinking water (either plain or in the form of other fluids or foods) is essential to your health.

“Think of water as a nutrient your body needs that is present in liquids, plain water, and foods. All of these are essential daily to replace the large amounts of water lost each day,” says Joan Koelemay, RD, dietitian for the Beverage Institute, an industry group.

Kaiser Permanente nephrologist Steven Guest, MD, agrees: “Fluid losses occur continuously, from skin evaporation, breathing, urine, and stool, and these losses must be replaced daily for good health,” he says.

When your water intake does not equal your output, you can become dehydrated. Fluid losses are accentuated in warmer climates, during strenuous exercise, in high altitudes, and in older adults, whose sense of thirst may not be as sharp.

Here are six reasons to make sure you’re drinking enough water or other fluids every day:

1. Drinking Water Helps Maintain the Balance of Body Fluids. Your body is composed of about 60% water. The functions of these bodily fluids include digestion, absorption, circulation, creation of saliva, transportation of nutrients, and maintenance of body temperature.

“Through the posterior pituitary gland, your brain communicates with your kidneys and tells it how much water to excrete as urine or hold onto for reserves,” says Guest, who is also an adjunct professor of medicine at Stanford University.

When you’re low on fluids, the brain triggers the body’s thirst mechanism. And unless you are taking medications that make you thirsty, Guest says, you should listen to those cues and get yourself a drink of water, juice, milk, coffee — anything but alcohol.

Five Reasons Water is So Important


Drink more water. We hear this all the time. We all know it is important, and we all know we should be doing it. But do we know why? Well, for starters, water makes up 60% of your total body weight, and a startling 90% of brain weight. Adequate hydration is essential for your body to function at all, let alone optimally. But if that isn’t enough to convince you, HealthyU brings you five fantastic reasons water is important to your health:

1. Water boots energy. Water delivers important nutrients to all of our cells, especially muscle cells, postponing muscle fatigue.

2. Water helps weight loss. Water helps you feel full longer, without adding any additional calories. Drinking water or eating foods with a high water content can be a big help in managing your weight.

3. Water aids in digestion. Water aids in constipation and other abdominal issues, especially those suffering from IBS. Water helps to move the digestive process along and through the system.

4. Water detoxifies. Moves toxins through your system faster, and optimizes kidney function. Inadequate hydration means inadequate kidney function.

5. Water hydrates skin. Forget expensive creams and cure-alls, water is the best defense against aging and wrinkles in the skin.

The guideline recommended amount is 8 glasses per day, though this varies from person to person. Those who exercise regularly, work outside, or have chronic medical conditions should consume more water to compensate for more water loss. Remember, water is your friend, and proper hydration is a key to good health.

Water: The Science of Nature’s Most Important Nutrient
Len Kravitz, Ph.D.
Water is colorless, tasteless and odorless. Because of its numerous and diverse functions in the body, it is often regarded as the most important nutrient. Most people can survive no more than 7 days without water (Williams, 2005). Although there is rigorous proof of its need for optimal health, scientists still have a difficult time objectively advising people how much they need to drink daily to maintain this favorable health. This article will explore into the depths of knowledge and research on this mysterious nutrient called H2O.
Water 101: The Basic Facts About Water in the Body?
Water is the most abundant constituent of the body, accounting for 50% to 60% of its mass. It is an inorganic (contains no carbons) substance composed of two hydrogen atoms which are bonded to one oxygen atom. Water is intricately involved in numerous functions of the body including the transport of oxygen, nutrients and waste products into and out of the cells. Drinking water contains several electrolytes (substances in solution that conduct an electric current) including calcium, chloride, fluoride, magnesium, potassium and sodium. Water is necessary for all digestion and absorption functions, and lubricates mucous membranes in the gastrointestinal and respiratory tracts. Even though it contains no calorie content, water is the medium for most chemical reactions in the body, especially those metabolic reactions involved in energy production. The body uses water as a coolant, helping to regulate body temperature during exercise, fever and in hot environments. Water also serves as a cushioning component between joints, in the spinal cord and in the brain.
How is Water Stored in the Body?
Water is stored in either intracellular fluid (ICF) or extracellular fluid (ECF) compartments. The ICF accounts for about 65% of the body water while the ECF (35%) is the blood plasma and lymph (a transparent, slightly yellow fluid that carries lymphocytes), which serve as the medium of transport for wastes and nutrients throughout the body. Minerals such as chloride, potassium and sodium participate in the maintenance of the ICF and ECF levels; a process governed by hormonal messages from the brain and the kidneys. If any molecule becomes too concentrated in one fluid compartment, it will pull water from the other compartment to dilute itself. For instance, eating pizza often makes a person thirsty. This is because the sodium from the pizza sauce and cheese (and meats) accumulates in the ECF, pulling water from the ICF. Cell sensors detect this change and signal the brain that the cell is dehydrating. The brain (specifically the hypothalamus) sends a signal to drink more water. So, whenever any minerals or molecules become too concentrated in one compartment (ICF or ECF), the brain will signal the body to drink more water until the compartment is appropriately diluted for homeostasis (maintenance of the body’s internal environment). If more fluid is present than desired at the cell, the kidneys proceed to make urine by filtering the excess fluid from the blood.
What is the Origin of the ‘Drink Eight 8-Ounce Glasses of Water a Day’ Advice?
For clarity, eight 8-ounce glasses is equal to 1,893 milliliters, or 2 quarts, or one-half a gallon, or approximately 1.9 liters. Most fitness professionals, nutritionists and personal trainers for years have encouraged clients to drink eight 8-ounce glasses of water a day. Surprisingly, no scientific evidence can be found that supports this “8 X 8” recommendation. In a superbly researched and written review, Heinz Valtin (2002) traces the origin of this recommendation to two possible sources. One source is an ‘unreferenced’ excerpt within a text (Nutrition for Good Health) authored by Drs. Fredrick Stare and Margaret McWilliams in 1974 which recommends around 6 to 8 glasses per 24 hours, and this can be in the form of coffee, tea, milk, soft drinks, beer, etc. However, Valtin highlights a much earlier origin in 1945 by the Food and Nutrition Board of the National Research Council which states ‘A suitable allowance of water for adults is 2.5 liters (which is approximately eight 8-ounce glasses) daily in most instances…’
So, What is the Current Daily Water Intake Recommendation?
The Institute of Medicine (IOM) published its Dietary Reference Intake for Water in February of 2004. This scientific committee established an adequate intake (AI) for total water to prevent the harmful (chiefly acute) effects of dehydration. It is essential to first note that every day close to a liter of water is lost from breathing, perspiring and in bowel movements. As well, the average urine output for adults is up to 1.5 liters a day. Consequently, the IOM AI for sedentary men and women (19-50 yr) is 3.7 liters and 2.7 liters per day, respectively. The committee explains that drinking fluids (water and beverages) represent about 81% of total water intake with 19% of water being provided by foods. So, the AI recommendation for actual fluid intake is 3.0 liters for men and 2.2 liters for women. Since 1 liter = 33.8 fluid ounces, men are recommended to drink 101.4 fluid ounces of beverages and drinking water (which is 13 cups {a cup is 8 fluid ounces}), and women are recommended to drink 74.4 fluid ounces (9 cups) of drinking fluids daily. The AI for girls 14-18 years is 2.3 liters/day (77.7 ounces or 9.5 cups) and 2.4 liters (81.1 ounces or 10 cups) for boys 14-18 years.
The Influence on Hydration on Health and Disease
Kidney Stones
Portis and Sundaram (2001) summarize several factors that may contribute to kidney stone formation including age (it is more common in adults versus elderly, but more common in elderly versus children), gender (it is two to three times more common in males then females), race (it is more common in Whites versus those of Asian ethnicity, who are more often affected than Blacks), climate (it occurs more frequently in hot, arid climates), and medications (drugs that treat swelling such as for congestive heart disease and cirrhosis of the liver). Portis and Sundaram continue that the most important factor influencing kidney stone formation is decreased fluid intake. To help prevent kidney stones, Hughes and Norman (1992) recommend moderation in the intake of calcium, oxalate (beverages such as beer, chocolate milk, teas, and fruit juices), protein, sodium and alcohol while increasing the intake of water and fiber.
Cancer of the Bladder and Lower Urinary Tract
The causes of bladder cancer include cigarette smoking and occupational exposure to aromatic amines (air contaminated by wild fires or coal tar). However it has also been clearly established that decreased water consumption is associated with bladder and lower urinary tract cancer (Altieri, La Vecchia and Negri, 2003). Altieri and colleagues theorize that the decreased fluid intake results in a greater concentration of carcinogens in the urine and/or prolonged contact with bladder mucous membranes.
Colorectal Cancer
Colorectal cancer is cancer that develops in either the colon or the rectum, which are parts of the body’s digestive system. From the small intestine, partly digested food enters the colon (the first five feet of the large intestine), which removes water and nutrients from the food and turns the rest into waste. The waste then passes from the colon into the rectum (the last six inches of the large intestine) and then out of the body. In most cases, colorectal cancers develop slowly over a period of several years. Researchers have theorized that low fluid intake (in conjunction with the fact that we excrete about 80-200 ml of water a day in waste) may increase the risk of colorectal cancer risk by increasing bowel transit time, thus increasing the carcinogen contact within mucous membranes in the colon and rectum (Altieri, La Vecchia, and Negri, 2003).
Breast Cancer
The association with fluid intake and breast cancer remains uncertain at this time. More research is needed to establish if any association exists.
Clinical Health
From a clinical point of view, any health-related body water deficit (e.g., sickness, diarrhea, vomiting or climatic stress) that challenges the ability of the body to maintain homeostasis can negatively impact physiological function and health. If these conditions continue for &Mac179; 24 hours a health practitioner should be consulted.
Hydration and Mental Performance
The research on hydration and mental performance is in its formative years. However, the science is clear that decrements in visuomotor (visual perception by the brain), psychomotor and cognitive performance can occur when 2% or more of the body weight is lost due to water restriction, heat or physical exertion (Grandjean and Grandjean, 2007).
Hydration and Physical Performance
According to Murray (2007) the literature discussing physical performance and hydration began in the late 1800’s. Murray summarizes that a decrease in body water below normal can stimulate inhibiting alterations in central nervous activity (reduced motivation and effort), cardiovascular function metabolic reactions and themoregulatory control mechanisms. A water loss, such as through dehydration, exceeding 2% of body weight (as little as 3 lbs {water} in a 150-lb athlete) can provoke these negative consequences. These deleterious physiological events are more severe warm in environments as compared to cold environments.
What are the Signs and First Aid of Dehydration and Heat Disorders?
The initial signs of dehydration may include light-headedness, headache, loss of appetite, flushed skin, dry sticky mouth, fatigue, dry eyes, muscle weakness, burning sensation in the stomach and a dark urine with a strong odor (Kleiner, 1999). As the dehydration worsens, Kleiner states that symptoms may include difficulty swallowing, clumsiness, sunken eyes, dim vision, numbness of the skin and muscle spasms. The one effective treatment for dehydration is to replace lost fluids with cool water. Sports drinks containing electrolytes and a carbohydrate solution may also help.
The three heat syndromes related to dehydration are heat cramps, heat exhaustion and heat stroke. Heat cramps are painful, brief muscle cramps that occur during exercise or work in a hot environment. Heat cramps usually involve the muscles fatigued by heavy exertion such as the calves, thighs, abdomen, and shoulders. Kleiner (1999) theorizes that the cramping is most likely due to the high sweat rates and dehydration disrupting the sodium and potassium ICF and ECF balance. Gradually cool down and begin to rest. Drink an electrolyte-containing (sports) drink while gently massaging and stretching the affected muscle groups. If the cramps continue for an hour seek medical assistance.
With heat exhaustion a person may go into hypovolemic shock (a state of decreased blood plasma and volume, characterized by pale, cool, clammy skin with a rapid heart rate and shallow breathing) and have some of the following symptoms: low or undetectable blood pressure, nausea, heavy sweating, low-grade fever, headache, and diminished consciousness. If you suspect heat exhaustion, get the person into a shady or air-conditioned location. Lie the person down and elevate the legs and feet slightly. Cool the person by spraying or sponging him/her with cool water and fanning. Have the person drink cool water. Heat exhaustion can quickly lead to heatstroke. If the symptoms start to worsen call immediately for medical assistance.
Heat stroke is an escalation of heat cramps and heat exhaustion. It is a life-threatening condition occurring when body temperature is 104 degrees (F) or higher. Sweating often stops as the body temperature is so high. Pulse rate may start to increase to about 130 b/min or higher (what is referred to as a sinus tachycardia). Seizures, lack of consciousness or hallucination may also occur. Lastly, weak muscles may become either more rigid or limp. Immediate medical intervention is needed to prevent brain damage, organ failure and/or loss of life.
What is the Proper Fluid Replacement to Sustain Endurance Exercise?
Failure to hydrate appropriately during exercise is a chief contributing factor to poor performance during endurance events, particularly in hot and humid conditions. The American College of Sport’s Medicine (ACSM) recently released its newest position stand on exercise and fluid replacement in an effort to guide exercisers towards safe and enjoyable participation in endurance exercise (Sawka et al., 2007). The next three sections, prehydrating before exercise, hydrating during exercise, and rehydrating after exercise, summarize key points from this ACSM position paper.
Prehydrating Before Exercise
The prehydration goal is to make certain that any fluid and electrolyte insufficiency is corrected prior to starting the cardiovascular exercise bout. Hydrating before the exercise can begin progressively about 4 hours before the workout session. About 5-7 mL/kg body weight (1 kg = 2.2 lbs) should be sufficient. So, if a person weighs 150 lbs, that weight is 68 kg; therefore 7 mL/kg X 68 kg = 476 milliliters of fluid. Since 8 ounces is equivalent to 237 milliliters, 476 millilers is about 16 ounces, or two glasses of water. Consuming some sodium-containing foods or snacks with the two glasses of water may help retain the fluid. A beverage with very light sodium (20¬-50 mEq per liter or 460-1150 milligrams per liter) would also suffice (note that mEq stands for milliequivalent).
Hydrating During Exercise
The hydration goal during exercise is to prevent excessive water loss and disparities in electrolyte balance in the working muscle cells. Hydration recommendations during exercise can be quite variable depending on a person’s sweat rate, mode of exercise, exercise duration, weather conditions, opportunities to hydrate, training status, heat acclimatization and exercise intensity. Because of the above circumstances, a customized hydration strategy is recommended that includes periodic hydration segments during the workout session. Sawka and colleagues (2007) clarify that prolonged (&Mac179; 3 hours) exercise is difficult to balance electrolyte and water deficits. Exercisers are encouraged to monitor their pre- and post-workout body weights during different workouts and try to match the weight loss (via sweat) with fluid replacement during the exercise. To sustain endurance exercise performance &Mac179; 1 hour, carbohydrate consumption (with a mixture of sugars such as glucose, fructose, maltodextrine, and sucrose) may be beneficial. Carbohydrate consumption at a rate of ~30-60 grams per hour has been shown to be quite effective in maintaining glucose levels for continuous aerobic performance beyond one hour (Sawka et al.). Sawka and fellow researchers add that the carbohydrate concentration should be up to 8%, and not beyond, because a higher concentration may impede gastric (stomach) emptying. Electrolyte needs during prolonged exercise are best replenished with fluids containing ~20-30 mEq per liter (460-690 milligrams per liter) of sodium and ~2-5 mEq per liter (80-200 milligrams per liter) potassium.
Rehydrating after Exercise
After exercise, the goal is to replenish any fluid or electrolyte shortfall. Sawka et al. (2007) suggest a resumption of normal of meals and snacks (that contain adequate sodium) with sufficient water to restore the body. The authors state the sodium losses are quite different between individuals and difficult to assess, but a variety of food choices supply the depleted electrolytes. Lastly, fluids are best absorbed by the cells of the body post-exercise when ingested gradually, as opposed to in single large amounts. As a general rule of thumb, for each kilogram (2.2 lbs) of weight post-exercise below the pre-exercise weight the body will need about 1.5 liters of fluid (Sawka et al.). Converting kg to lb, for each pound of sweat you lose in exercise, drink about 25 ounces of fluid post-exercise for replenishment.
Water is the most omnipresent substance on our planet. Life as we know it could not exist without water. Yet some unique physical properties are poorly understood. For instance, why does water expand, instead of contracting, when it freezes?, or why does water store heat better than virtually any other fluid?, or how is it that two atoms of hydrogen and one atom of oxygen, both flammable gases, are able to combine and become a liquid. The unique properties of water place limits on our physiology and anatomy while simultaneously providing the opportunities for physical activity, exercise and life as we know it. Yet, there is so much more yet to learn about this mysterious molecule we call H20.
Side Bar 1: 15 Frequently Asked Questions on Water
1) Why do you need to drink more water with air travel?
The re-circulated air on airplanes has less moisture. The travel time at high altitudes also increases your water loss through evaporation. As a general guide, drink one 8-ounce glass of water or juice for each hour of flying time.
2) Why do men have a higher percent of water than women?
Men have a slightly high percent of muscle mass in the human body and muscle is composed of about 75% water.
3) Why does your sweat vary on workouts during the week.
The total ‘rate’ of sweating as well as the total ‘sweat loss’ can be markedly different from day to day due to differences in the environment (heat and humidity), exercise intensity, exercise duration, mode of exercise (the less accustomed to the activity, usually the more work and sweat loss) and type of clothing (water absorbency). {see answer to question #7 to learn how to calculate exercise sweat rate}
4) How much water can be lost in an hour of exercise?
Doing light exercise in a cool or moderate environment the sweating rate might be as little as 100 ml/hour, which is about 3 ounces. However, during vigorous exercise in a hot environment the sweat loss can be over 3,000 ml/hour, which is about 100 ounces (Murray, 2007).
5) How does age effect your ability to hydrate?
Drinking only in a response to the body’s thirst signals increases an older adult’s risk of becoming dehydrated; because with age, thirst becomes a less effective indicator of the body’s fluid needs. Seniors who have relocated to locations where the weather is warmer or dryer than the climate they are accustomed are also more susceptible to become dehydrated. They need to drink water regularly. Dehydration in children usually results from losing large amounts of fluid (such as from play) and not drinking enough water to replace the loss. An infant can become dehydrated only hours after becoming ill. Dehydration is a major cause of infant illness and death throughout the world.
6) Physiologically, why don’t colder environments impair physiological function as much as hot environments?
There is performance impairment associated with colder environments. However, dehydration is not as deleterious because cardiac output (heart rate x stroke volume) is higher in colder environments (enhancing cardiovascular performance) while core temperature is lower (Murray, 2007).
7) How can you determine your sweat rate.
To determine sweat rate, measure body weight before and after exercise (wearing no clothes), the amount of fluid consumed during exercise, and the amount of urine excreted (if any) during exercise.
Follow the example below to calculate sweat rate (Williams, 2005):
a. Pre-exercise body weight 130 lbs
b. Post-exercise body weight 126.5 lbs
c. Change in body weight -3.5 lbs (or 56 ounces)
d. Drink Volume 16 ounces
e. Urine Volume 0 ounces
f. Sweat loss (c + d – e) 72 ounces
g. Exercise time 45 minutes
h. Sweat Rate (f divided by g) 72 ounces/45 minutes = 1.67 ounces/minute
Sweat rate varies from person to person due to body weight differences, genetic factors, heat acclimation ability and metabolic (energy production) efficiency (Sawka, 2007).
8) Please explain about the different types of water, including herbal, vitamin, purified, spring, mineral and artesian.
a. Herbal water features flavors derived from herbs that tout health benefits associated with antioxidants.
b. Vitamin water is fortified with various vitamins and other additives, including a sweetener that adds calories to the drink.
c. Purified water is usually produced by some type of distillation process.
d. Spring water flows naturally from an underground source.
e. Mineral water comes from a protected underground source and must contain some minerals.
f. Artesian water is drawn from a well that taps a confined aquifer (underground layer of water permeable rock, sand, clay or silt).
9) What is the composition of sweat?
Although this varies from person to person, the composition of sweat is approximately 99% water and the electrolytes sodium and chloride (Williams, 2005). Williams notes that other minerals lost in tiny amounts include calcium, potassium, magnesium, iron, zinc, copper and some water-soluble vitamins.
10) Besides counting daily cups of water intake, is there a way to monitor whether you are drinking enough or too much water?
As a general rule of thumb, urine color is a good ‘marker’ of water intake. Urine is composed of water, urea (metabolic waste), organic materials (including small amounts of carbohydrates, enzymes, fatty acids and hormones) and some electrolytes. Normal urine should be clear to amber (light yellow) in color. It is often more yellow if taking vitamins and some medications. Urine that is a dark yellow and lower volume output (than usual for you) are indicators of dehydration.
Drinking too much water can lead to a “water intoxication”. However, this instance is rare in healthy persons because the kidneys can produce a large quantity of urine in a brief time period to correct this imbalance. A surplus of water intake may also lead to greater exposure to pollutants in the water, if sustained for an extended period of time.
11) Will drinking water help with weight loss?
There is some evidence for men and women that water intake with a meal may help to promote satiety and take the edge off hunger (Valtin, 2002). Water has no caloric value and when substituted for sweetened (usually with high-fructose corn syrup or sucrose) beverages, that add calories with few other nutrients, it will provide a positive modification to a weight management plan.
12) Why do some athletes wet their body during endurance competition events?
Sponging the head and torso with cold water or a water spray is a skin wetting technique. Although perceived to be performance enhancing, this practice has not been demonstrated to reduce core temperature or improve cardiovascular performance.
13) Do women who are pregnant or breast feeding need to drink more water?
Yes, expectant mothers and those who are breast-feeding need additional fluids daily to stay hydrated. Women at risk of gaining too much weight are encouraged to consume more water (no calories) and limit their consumptions of sweetened fluids (with calories).
14) What is hyponatremia?
Hyponatremia (“natremia” comes from the Latin word for sodium, and means “sodium status”) means subnormal levels of sodium in the blood. This may occur in prolonged cardiovascular events such as a marathon. Symptoms include vomiting, headache, bloating, swollen feet and hands, disorientation, undue fatigue and wheezy breathing. Fluid intake overload is the main cause of exercise-induced hyponatremia. An excessive loss of total body sodium is another cause or contributing reason. Medical intervention is necessary in order to clearly discern whether symptoms are from a heat disorder or hyponatremia.
15) Is cold water absorbed faster in the body than warm water?
No, however cool or lukewarm water is soothing to the taste and absorbed faster in the body.
Side Bar 2: Definition of Terms Associated with Hydration
Electrolyte: A substance in solution that can conduct an electric current. Electrolytes in the human body include calcium, chloride, fluoride, magnesium, potassium and sodium.
Euhydration: A normal state of body water content also called normohydration.
Dehydration: The loss of water (due to exercise, illness, environment, medications {such as diuretics}, or fluid deprivation) and salts essential for normal body function.
Hydration: To supply water to in order to restore or maintain fluid balance.
Hypohydration: The removal of water from the body.
Hyperhydration: A state of excess fluids in the body, also called overhydration.
Hyperthermia: An acute condition which occurs when the body produces or absorbs more heat than it can dissipate.
Hyponatremia: An abnormally low concentration of sodium in the blood. Too little sodium can cause cells to malfunction, and extremely low sodium can be fatal.
Hypovolemic shock. A state of decreased blood plasma and volume, characterized by pale, cool, clammy skin with a rapid heart rate and shallow breathing. Also called physical collapse.
Osmolality: The amount or concentration of dissolved substances (known as solute) in a solution.
Osmosis: Diffusion of fluid through a semipermeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal concentration of fluid on both sides of the membrane.

Altieri, A., La Vecchia, C. and Negri, E. (2003). Fluid intake and risk of bladder and other cancers. European Journal of Clinical Nutrition, 57(Suppl. 2), s59-s68.
Grandjean, A.C. and Grandjean, N.R. (2007). Dehydration and cognitive performance. Journal of the American College of Nutrition, Vol. 26(90005), 549s-554s.
Hughes, J. and Norman, R.W. (1992). Diet and calcium stores. Canadian Medical Association Journal, 146(2), pp. 137-143.
Institute of Medicine. Executive Summary. Dietary reference intakes for water, potassium, sodium, chloride, and sulfate. National Academy of Sciences, Food and Nutrition Board, National Academy Press, 2004.
Kleiner, S.M. (1999). Water; An essential but overlooked nutrient. Journal of the American Dietetic Association, 99, 200-206.
Murray, B. (2007). Hydration and physical performance. Journal of the American College of Nutrition, 26(5), 542s-548s.
Portis, A.J. and Sundaram, C. P. (2001). Diagnosis and initial management of kidney stones. American Family Physician, Vol. 63(7), pp. 1329-1338.
Sawka, M.N., Burke, L.M., Eichner, E.R., Maughan, R. J., Montain, S.J., and Stachenfield, N.S. (2007). American College of Sports Medicine Position Stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise, Vol. 39, pp. 377-390.
Valtin, H. (2002). “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 X8”? American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, 283: R993-R1004.
Williams, M.H. (2005). Nutrition for Health, Fitness & Sport 7th Edition. McGraw Hill Higher Education.

The Health Benefits of Water

Water Aids in Digestion

Digestion starts with saliva, the basis of which is water. Digestion relies on enzymes that are found in saliva to help break down food and liquid and to dissolve minerals and other nutrients. Proper digestion makes minerals and nutrients more accessible to the body. Water is also necessary to help you digest soluble fiber. With the help of water, this fiber dissolves easily and benefits your bowel health by making well-formed, soft stools that are easy to pass.

Water Prevents You From Becoming Dehydrated

Your body loses fluids when you engage in vigorous exercise, sweat in high heat, or come down with a fever or contract an illness that causes vomiting or diarrhea. If you’re losing fluids for any of these reasons, it’s important to increase your fluid intake so that you can restore your body’s natural hydration levels. Your doctor may also recommend that you drink more fluids to help treat other health conditions, like bladder infections and urinary tract stones. If you’re pregnant or nursing, you may want to consult with your physician about your fluid intake because your body will be using more fluids than usual, especially if you’re breastfeeding.

How Much Water Do You Need?

There’s no hard and fast rule, and many individuals meet their daily hydration needs by simply drinking water when they’re thirsty, according to a report on nutrient recommendations from the Institute of Medicine of the National Academies. In fact, most people who are in good physical health get enough fluids by drinking water and other beverages when they’re thirsty, and also by drinking a beverage with each of their meals, according to the Centers for Disease Control and Prevention. If you’re not sure about your hydration level, look at your urine. If it’s clear, you’re in good shape. If it’s dark, you’re probably dehydrated.

About 60 percent of the average adult human body is made of water, according to a National Institutes of Health report. This includes most of your brain, heart, lungs, muscles and skin, and even about 30 percent of your bones. Besides being one of the main ingredients in the recipe for humankind, water helps us regulate our internal temperature, transports nutrients throughout our bodies, flushes waste, forms saliva, lubricates joints and even serves as a protective shock absorber for vital organs and growing fetuses.

There’s no dispute that water is crucial to a healthy life (or any life at all, for that matter). And yet, there’s little scientific consensus about the exact amount of the stuff an individual should consume each day. So how much water do you actually need to drink to be healthy?

You may have heard that you should drink eight 8-ounce (237 milliliters) glasses of water a day (totaling 64 ounces, or about 1.9 liters). That’s the wrong answer. Despite the pervasiveness of this easily remembered rule, there is no scientific evidence to back it up, according to a 2002 review of studies. In fact, numerous studies suggest that this is far more actual drinking water than is necessary for most healthy adults.

The problem with this rule, researchers say, is that drinking water by the glass is not the only way that humans hydrate. Yes, it’s true that guzzling H2O is an inexpensive and calorie-free way to whet your whistle, but the “8 x 8” rule crucially overlooks two big sources of daily water consumption.

Food and drink

One such source is food. Everything you eat contains some water. Raw fruits and vegetables have a lot; fruits such as watermelons and strawberries, for example, are more than 90 percent water by weight, according to the U.S. Department of Agriculture. Different diets naturally contain different amounts of water, but it adds up. According to a 2004 report by the National Academies of Sciences, the average North American gets about 20 percent of his or her daily water intake through food, and that counts toward healthy hydration.

The other key water sources that the “8 x 8” rule overlooks are other beverages. Non-alcoholic drinks such as coffee, tea, milk, juice and soda contain mostly water, and all contribute to your hydration. Contrary to another popular myth, studies show that coffee does not dehydrate you and is a suitable form of H2O intake. (Just remember that there can be adverse side effects of drinking too much caffeine, including headaches and disrupted sleep.)

So, between all the food, water, and other fluids you consume in a day, how much water should you aim to imbibe? The National Academies of Sciences suggests that women consume a total of approximately 2.7 liters (91 ounces) of water from all beverages and foods each day and that men get approximately 3.7 liters (125 ounces) daily. But these are just general guidelines and are not supported by firm scientific studies.

The truth is, there is no magic formula for hydration — everyone’s needs vary depending on their age, weight, level of physical activity, general health and even the climate they live in. The more water you lose to sweating, the more water you’ll need to replace with food and drink. So, naturally, a person doing strenuous physical work in a hot, tropical climate would need to drink more water than a person of identical weight and height who spent the day sitting in an air-conditioned office.

If you are looking for concrete advice, though, the best place to look is within.

“The vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide,” according to the National Academies of Sciences. Your body naturally feels thirsty when your hydration levels are dropping, and water is the best medicine. (On the other end of the digestive spectrum, your urine can also tell you whether you’re getting enough to drink — dark yellow or orange urine usually indicates dehydration, while well-hydrated urine should look pale yellow or colorless.)

The bottom line: Drink up when you’re thirsty, and drink more when you sweat more. Your body will take it from there.

Originally published on Live Science.

Do We Really Need to Drink Water?

A look at how various beverages hydrate compared with water.

Our bodies are mainly made up of water—somewhere between 75 percent of our bodies when we are infants and 55 percent of our bodies in our golden years. And numerous studies show that drinking water has benefits: It helps us think better, it may help increase the body’s ability to burn fat and it may help increase the amount of calories some individuals burn. A 2016 French study found that those who drank more water had better-quality diets. This is all well and good, but do we really need to drink water?

“There is no need to drink water and, if water needs are low, there is no need to drink anything at all if a diet rich in fruits and vegetables and other foods with a high water content are chosen,” says Dr. Ron Maughan, a visiting professor at the University of St. Andrews School of Medicine in Scotland and a member of the science advisory board of the European Hydration Institute. However, the average American gets only about 20 percent of his or her water intake from food, according to a 2010 study in “Nutrition Reviews.”

So if our bodies don’t technically need water, does that mean any beverage will hydrate us?

Water: The gold standard?

When it comes to studying hydration, water is the control to which science compares everything else. And to understand how other beverages stack up to it, it’s important to understand how you absorb the water you drink.

Like most nutrients, water is absorbed in the small intestine. The small intestine absorbs a lot of water—roughly 1 to 2 liters per day plus another 6 to 7 liters that come from your body’s own secretions of saliva and from other organs, such as the stomach and liver. Eighty percent of these fluids have been absorbed by the small intestine—or have traveled through the cell membrane in a process known as osmosis—before they reach the large intestine.

The thing about water osmosis is that it is dependent on the amount of sodium in the body. Sodium and other electrolytes help the body hold on to water and maintain a fluid balance. Fluid balance is when the amount of electrolytes in the various body fluids, such as blood and urine, are within healthy ranges. Maintaining this balance of electrolytes helps your body’s blood chemistry, muscle action and other processes. Sodium, calcium, potassium, chlorine, phosphate and magnesium are all electrolytes.

“Drinking large volumes of plain water will increase body water content, but regulatory mechanisms mean that this is quickly excreted,” Maughan says. “Drinks with a high sugar concentration will be emptied from the stomach more slowly and will be more slowly absorbed, so they may stay in the body for longer,” Maughan continues. “Likewise, salt added to drinks or salty food added to drinks will help retain water in the body—the salt acts like a sponge, holding the water in the body.” Knowing this, read on to learn about how various beverages hydrate the body.

Coconut water vs. water

If you listen to the hype surrounding coconut water, you may think that it is nature’s sports drink or even that it hydrates better than water. According to the Academy of Nutrition and Dietetics, coconut water isn’t the perfect sports drink because it doesn’t replace the amount of calories, sodium and electrolytes that are lost through vigorous exercise that sports drinks do.

However, in a head-to-head comparison published in the “Journal of Physiological Anthropology and Applied Human Science,” coconut water provided comparable hydration to sports drinks and plain water in eight subjects who had worked out at 60 percent of their maximum effort in a warm environment until 2 percent of their body weight was lost through sweat. This small, preliminary study shows that coconut water can rehydrate you after vigorous exercise but no faster or better than plain water.

If sports drinks upset your stomach, one of the side findings of the study was that coconut water caused less nausea, less fullness and no stomach upset. So in this case, coconut water can help to rehydrate you and maintain some fluid balance.

Coffee and tea vs. water

It is a myth that caffeinated drinks, such as tea and coffee, cause dehydration. “It is unlikely that anyone gets dehydrated from drinking coffee or other caffeine‐containing beverages. Telling people not to drink tea, coffee or cola is likely to cause dehydration as people do not replace these with equal volumes of other drinks. There is some habituation to caffeine but not as much as might be thought,” Maughan says.

In fact, research that showed caffeine caused dehydration was done over short periods of time using high-strength caffeine pills at intakes of 200–500 milligrams of caffeine per dose—much higher than the amount in tea (40–50 milligrams), coffee (75–100 milligrams) or energy drinks (80–120 milligrams). “Caffeine does have a diuretic effect, but it takes a fairly large dose to get that effect—typically at least 250 to 300 milligrams, which is far more than you will get from the average cup of coffee, unless you drink a ‘grande’ size,” states Maughan. “Regular caffeine users will be less affected than those who never consume caffeine, but there is still an individual variability in response that is not well-understood.”

Ultimately, it’s the caffeine content that matters, as does the amount of water you consume at the same time, says Carrie Ruxton, a doctor and registered dietitian who has studied the effects of caffeine in tea on the body. “So an espresso (high caffeine, small volume) would be more likely to dehydrate than a large mug of tea with milk (low caffeine, large volume). However, caffeinated drinks are mostly water, which offsets the effect of caffeine.”

Juice vs. water

Maughan’s research, published in the “American Journal of Clinical Nutrition,” looked at the hydrating capabilities of 13 different beverages, including water. Orange juice, which is made up of 89 percent water and contains some potassium and carbohydrates, was found to be effective at maintaining fluid balance within the body over a longer period of time compared with water. In fact, his research found that “drinks containing the highest macronutrient and electrolyte contents were the most effective at maintaining fluid balance.”

Sports drinks vs. water

Almost any fluid is hydrating. “There are going be times when plain water is all you need,” says Laura Daray, senior scientist at the Gatorade Sports Science Institute, “for instance, throughout a typical day, for shorter workouts or for very low sweating types of conditions. Then, there are going to be instances where an electrolyte-containing water may be a better fit for you.”

When you lose sodium through sweat, sometimes you need electrolytes to truly rehydrate and replenish the water your body has lost. Electrolytes are usually contained in sports drinks.

“Sodium is going to help with fluid retention, and this means it’s going help an individual hang on to more of the fluid that he or she is consuming, as opposed to losing it through urination. Sodium’s also going help drive thirst. This mean that it’s going help a person voluntarily drink more, and do a better job at replacing fluid losses, as opposed to when just drinking plain water,” Daray explains.

And as Maughan’s research found, sports drinks hydrate as well as water does—and help maintain fluid balance.

Sparkling water vs. water

When it comes to hydrating with water, whether your water has bubbles in it or not doesn’t really make a difference. “There may be small differences, but these are trivial,” says Maughan.

Ultimately, drinking any beverage will help keep you hydrated. Knowing how your body reacts to each one will help you decide the right hydrator for you.

Your Body on Dehydration

When your body doesn’t have enough water, it sends signals. Use these clues to help decode its hints:

Head—Headache, dizziness

Mouth—Thirst and bad breath

Heart—Sluggishness and heart beating harder or faster; dehydration makes your blood thicker, and it becomes harder for the heart to move blood through the vessels

Stomach—Sweets cravings; when dehydrated, your body has a difficult time creating glycogen

Bladder—Decrease in urination, dark-colored urine

Legs—Muscle cramps

Skin—Dry skin

Photo credits: studiovespa, Adobe Stock; 5ph, Adobe Stock; Brent Hofacker, Adobe Stock; robert, Adobe Stock; Kar Tr, Adobe Stock; caprasilana, Adobe Stock

Why Drinking Water Is the Way to Go

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What do you, the trees, and a hamster have in common? Give up? You all need water. All living things must have water to survive, whether they get it from a water fountain, a rain cloud, or a little bottle attached to the side of a hamster cage.

Without water, your body would stop working properly. Water makes up more than half of your body weight, and a person can’t survive for more than a few days without it. Why? Your body has lots of important jobs and it needs water to do many of them. For instance, your blood, which contains a lot of water, carries oxygen to all the cells of your body. Without oxygen, those tiny cells would die and your body would stop working.

Water is also in lymph (say: limf), a fluid that is part of your immune system, which helps you fight off illness. Water helps keep your temperature normal. You need water to digest your food and get rid of waste. Water is needed for digestive juices, urine (pee), and poop. And you can bet that water is the main ingredient in perspiration, also called sweat.

Besides being an important part of the fluids in your body, water is needed by each cell to work.

Your body doesn’t get water only from drinking water. Any fluid you drink will contain water, but water and milk are the best choices. Lots of foods contain water too. Fruit contains quite a bit of water, which you could probably tell if you’ve ever bitten into a peach or plum and felt the juices dripping down your chin. Vegetables also contain a lot of water — think of slicing into a fat tomato or crunching into a crisp stalk of celery.

How Much Is Enough?

Because water is so important, you might wonder if you’re drinking enough. There is no magic amount of water that kids need to drink every day. The amount kids need depends on their age, body size, health, and activity level, plus the weather (temperature and humidity levels).

Usually, kids drink something with meals and should definitely drink when they’re thirsty. But if you’re sick, or it’s warm out or you’re exercising, you’ll need more. Be sure to drink some extra water when you’re out in warm weather, especially while playing sports or exercising.

When you drink is also important. If you’re going to sports practice, a game, or just working out or playing hard, drink water before, during, and after playing. Don’t forget your water bottle. You can’t play your best when you’re thinking about how thirsty you are!

When your body doesn’t have enough water, that’s called being dehydrated. Dehydration also can keep you from being as fast and as sharp as you’d like to be. A bad case of dehydration can make you sick. So keep that water bottle handy when the weather warms up! Not only does water fight dehydration, but it’s refreshing and has no calories.

Your body regulates the amount of water in your system. The body holds on to water when you don’t have enough or gets rid of it if you have too much. If your pee is very light yellow, you are well hydrated. When your pee is very dark yellow, it’s probably time to drink up.

You can help your body by drinking when you’re thirsty and drinking extra water when you exercise and when it’s warm out. Your body will be able to do all of its wonderful, waterful jobs and you’ll feel great!

Reviewed by: Mary L. Gavin, MD Date reviewed: June 2018

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