Water’s Role in the Body

Water’s Role in the Body

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Water helps nearly every part of the human body function efficiently. Considering that our bodies are almost two-thirds water, it is important to understand water’s role in healthy lifestyles.

According to Lawrence Armstrong, PhD, FACSM, professor emeritus, University of Connecticut, and Drinking Water Research Foundation (DWRF) trustee, “Our thirst sensation doesn’t really appear until we are 1 or 2 percent dehydrated. By then dehydration is already setting in and starting to impact how our mind and body perform.” According to Armstrong, “Dehydration affects all people, and staying properly hydrated is just as important for those who work all day at a computer as it is for marathon runners, who can lose up to 8 percent of their body weight as water when they compete.”

The body parts

Water is essential for life. It supports metabolic reactions—such as the formation of urine (approximately 95 percent water), sweat (approximately 99 percent water), and blood plasma (about 92 percent water). Other parts of the body function best when adequately hydrated. Here are a few examples.

Brain. Our brains are 83 percent water, and numerous studies have demonstrated the positive benefits of adequate water consumption and the negative impacts of dehydration. Your brain’s hydration status can affect all of the following: cognitive function, mood, motor function, short- and long-term memory, and attention span. Corinne Cian, PhD, a researcher from the Armed Forces Biomedical Research Institute in France, found that dehydration of 2.8 percent caused impaired performance on tasks including examining visual perception, short-term memory, and psychomotor ability. So, the next time you are feeling cranky, have a hard time focusing, or can’t think properly, perhaps you should reach for some bottled water—because you may simply be dehydrated.

Muscles. While water loss degrades many physiological functions, one of the most obvious is diminished muscle performance. “Muscles need water to be able to expand and contract quickly in response to instructions from the nervous system. Muscle strength is also affected by hydration: Thirsty muscles move slowly and can’t bear as much weight, which leads to sluggish performance. This effect is present in any dehydrated person—not just elite athletes,” says Georgie Adams, PT, A Fine Balance.

Joints. Proper hydration is also critical for healthy joints. “Water acts as a lubricant for your joints, making sure they can move efficiently and painlessly. Many joints have little fluid-filled sacs called bursae in them. These cushion the joint and allow it to move freely and bear weight. Poor hydration can mean these little sacs become thinner and more rigid which makes them unable to provide proper joint support,” says Adams.

Gastrointestinal functions. Properly hydrating the colon will promote regular peristalsis (the natural muscle contractions that move food through the intestines) and help ease elimination. Try to drink at least half your body weight in ounces of water each day, says gastroenterologist Leonard Smith, MD, of Gainesville, Florida.

Kidney functions. Ten percent of the U.S. population is affected by kidney stones—and that figure is growing. Researchers, such as Jessica Sontrop, PhD, from Western University in Canada, have found increased water consumption can alleviate the incidence of kidney stones because water helps decrease the concentrations of substances involved in stone formation. In addition, Sontrop has found the prevalence of stage III chronic kidney disease was highest among those with the lowest water intake. Her study concluded there is “evidence suggesting a potentially protective effect of higher total water intake, particularly plain water, on the kidney.”

Heart functions. Keeping the body hydrated helps the heart more easily pump blood through the blood vessels to the muscles. And, according to the American Heart Association, it helps the muscles work efficiently. “If you’re well hydrated, your heart doesn’t have to work as hard,” says John Batson, MD, a sports medicine physician with Lowcountry Spine & Sport in Hilton Head Island, South Carolina, and American Heart Association volunteer.

Regulation of blood volume. Decreases in blood volume can occur through blood loss or via loss of body water from sweating, which can lead to increased heart rate, a drop in blood pressure, or fainting. Drinking water will reduce heart rate and increase blood pressure in normal healthy people, says Barry Popkin, PhD.

Gallbladder functions. Studies have found that a high daily water intake and consumption of water at regular intervals can help with the function of emptying the gallbladder and preventing gallstones from forming, according to research by Mahantayya V. Math.

Urinary tract. Numerous studies have found that drinking plenty of water can help “flush out” bacteria from the urinary tract. One such study by Christine Stauffer, MD, of University Hospital in Bern, Switzerland, found girls with poor fluid intake were three times more likely to have recurring urinary tract infections compared to better-hydrated girls. That research is significant because urinary tract infections are the second most common reason antibiotics are prescribed (respiratory infections are No.1), coupled with a general growing concern over implications connected to the “overuse of antibiotics” among the population.

Skin elasticity and resilience. Water makes up 30 percent of our skin, so it makes sense that water contributes to our skin’s plumpness, elasticity, and resiliency. While maintaining adequate hydration cannot stop wrinkles, Professor Martina Kerscher, MD, Division of Cosmetic Sciences, University of Hamburg, found that water helped with skin thickness and density among people who had low water intake.

Controlling and losing weight. Drinking water in place of caloric beverages will reduce a person’s energy intake, which helps better control daily calorie intake. For people who are overweight and trying to lose pounds, there is evidence that drinking water will also alter metabolism. Jodi Stookey, PhD, of Children’s Hospital Oakland Research Institute (CHORI) in California, found that increases in water consumption were associated with significant loss of body weight and fat in overweight dieting women, regardless of diet and activity. Stookey has pointed out that studies examining how athletes improved athletic performance by burning more carbohydrates and less fat to delay fatigue during intense physical activity could reveal information about weight loss and water. According to Stookey, “When the same studies are looked at from a weight-loss perspective instead, we’re left with only one question, What are we waiting for? We should absolutely be telling people to drink water as part of losing weight. Carbohydrate and fat metabolism are linked like a see-saw. If you prioritize one, you suppress the other.”

Situations that require special consideration

Knowing that water consumption is necessary for a healthy body is one thing, but it’s also important to be aware that situations exist when it is particularly important to have access to water.

Patients, physically impaired, and the elderly. A variety of physiological conditions can affect patients, physically impaired persons, and the elderly that don’t bother a healthy middle-aged person—such as a reduced sense of thirst, decreased total body water content, and decreased kidney function—which makes them more susceptible to becoming dehydrated. But oftentimes, a decrease in mobility causes that group to purposely put off drinking fluids, so they don’t have to go to the bathroom as often, as getting up and down is difficult and they feel they could risk injury. However, studies show patients with high water intake are less likely to have a fatal heart attack. In addition, research by Professor Luca Masotti, MD, at the School in Geriatrics, University of Siena, Italy, shows well-hydrated patients recover quicker. And a study by Mathilde Ferry, at the Centre Hospitalier Universitaire in France, shows patients with high water intake have lower rates of infections.

Air travel. Aircraft cabin air lacks humidity, which can cause moisture in our bodies to evaporate more quickly than normal, causing us to become dehydrated. Research by Wolfgang Schobersberger, of the Medical Informatics and Technology (UMIT) in Austria, has shown that dehydration increases systolic blood viscosity, which is associated with blood clots. The advice is to drink plenty of water before your flight, and sip regularly during a flight to prevent dehydration.

Cold weather. Researchers at the University of New Hampshire (UNH) used “cold chambers” to study the effects of cold on the human body. According to Robert Kenefick, PhD, UNH associate professor, cold temperatures actually alter thirst sensation. By measuring blood volume and flow, he discovered the brain focuses more on body core temperature over fluid balance. “If humans don’t naturally hydrate themselves properly, they can become very dehydrated in cold weather because there is little physiological stimulus to drink,” says Kenefick. Coupled with this loss of thirst sensation, cold weather causes decreased body water due to respiratory fluid loss through breathing, greater effort during physical activity because of the weight of extra clothing, and sweat evaporating more quickly due to the cold air.

Extreme heat. The Centers for Disease Control and Prevention (CDC) suggests that during hot weather people need to increase their fluid intake, regardless of activity level. And people shouldn’t wait until they feel thirsty before they consume fluids. During heavy exercise in a hot environment, the CDC says a person should drink two to four glasses (16-32 ounces) of cool fluids each hour. Also avoid very cold drinks because they can cause stomach cramps.

Are you hydrated? 

The best way to keep on top of your hydration is to keep an eye on the color of your urine. Armstrong has provided a urine color chart on his website that can help people tell their level of hydration. The palest yellow indicates “adequate hydration,” says Armstrong. On average, men urinate 1.4 liters per day, and women urinate 1.1 liters per day, so it’s important to consume at least that much and then more to compensate for other body water lost through normal sweating and breathing.

Water’s role in your body is extremely important. Use our hydration calculator to help you determine the proper amount of water your body requires.

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