Running a marathon involves a lot of sweating. So you might figure that runners would be awfully dehydrated by the end of a race, even if they are conscientious about drinking plenty of water.
A study in The New England Journal of Medicine tested this idea. It looked at hydration among runners in the Boston Marathon.
The results were surprising.
Researchers found that 13% actually were suffering from over-hydration after the race. About 1% were in the critical range, meaning they were in danger of suffering life-threatening complications from drinking too much water.[i] [ii]
Meanwhile, not a single runner was found to be severely dehydrated.
The medical name for over-hydration is hyponatremia. It occurs when you drink so much water that your body can’t rid itself of the surplus fast enough through sweating or urination. This dilutes sodium in your blood, which you need to maintain stable blood pressure and to regulate your heart rate.[iii]
When you drink too much water, your body responds by moving the excess water from your blood into surrounding tissue. This causes cells to swell like water balloons. When your brain cells start to swell, you get a headache. If you drink more water, eventually you lose consciousness.
No one keeps statistics on hyponatremia deaths. But in recent years, they have been reported not only in runners, but in high school football players, U.S. Army soldiers, a police officer participating in a charity bike ride, a college student doing calisthenics, and a canoe paddler.[iv]
A 2017 study in the journal Frontiers in Medicine found that water overdoses send many to the hospital. They include people doing yoga, walkers, weightlifters, and hikers.[v]
On the flip side, how many people does dehydration kill?
A review of 15 studies looked at hydration among people participating in sports. The researchers concluded:
“There seems to not be a single case of death resulting from sports-related dehydration in the medical literature.”[vi]
Many of us spend our days with a water bottle because we’ve been told that more is better when it comes to hydration.
We’ve been told that drinking lots of water:
- Makes our skin healthier
- Flushes toxins
- Improves our athletic performance
- Stops you from mistaking thirst for hunger
Let’s examine the science behind each of these claims…
Does drinking more water make your skin healthier?
Dr. Aaron Carroll is a professor at the Indiana University School of Medicine. “Reviews have failed to find that there’s any evidence that drinking more water keeps skin hydrated and makes it look healthier or wrinkle-free,” he said.
Research published in the journal Clinics in Dermatology looked at hydration and skin health in 86 people. Half the subjects drank extra water every day, making sure they consumed at least two quarts. The other subjects drank no extra water.
After four weeks, neither group had any perceptible skin changes.[vii]
Dr. Lawrence E. Gibson of the Mayo Clinic said there are no quality studies showing that drinking more water improves skin health. “There’s a lack of research showing that drinking extra water has any impact on skin hydration or appearance,” he said.[viii]
Dry skin is an external problem that should be treated with moisturizers or by avoiding harsh soaps and hot showers, he said.
In some cases, drinking extreme amounts of water can temporarily cause bloating that may make a person’s face look fuller, Dr. Gibson said. But this is not healthy and causes no structural improvements to the skin, he said.
Does drinking more water flush toxins from your body?
A 2018 study in the Journal of the American Medical Association looked at this question. Researchers wanted to know if they should recommend that kidney disease patients drink more water, since toxin removal is critical to their health.[ix]
They split 630 patients into two groups. One drank more water. The other did not.
After a year, there was no difference in toxin levels or kidney function between the two groups.
Dr. Stanley Goldfarb is a kidney expert at the University of Pennsylvania. He says that drinking extra water actually causes your body to retain more toxins, not flush them.
After you drink water, it goes through your digestive system into your bloodstream. This causes your blood volume to increase. Your kidneys then have more blood to filter.
With normal hydration, your entire bloodstream passes through your kidneys about 60 times a day. With the added blood volume caused by drinking extra water, that number goes down. Your kidneys filter your bloodstream fewer times a day, so they remove less toxins.[x]
“Drinking large amounts of water surprisingly tends to reduce the kidneys’ ability to function as a filter,” Dr. Goldfarb said.[xi]
Does drinking water before exercising improve your performance?
“Some of the fastest marathon times are in athletes who drink very little,” said Dr. Mitchell Rosner. “There’s no evidence that a little bit of dehydration really impacts anybody’s performance.”
Dr. Rosner is a kidney specialist at the University of Virginia who studies hydration in athletes. To optimize performance, most athletes should simply drink water when they feel thirsty, he said.
But there are exceptions. You should consider hydrating before activities that involve extreme sweating or if the sport doesn’t allow you to take drink breaks, Dr. Rosner said.
One of the complicating factors is that a headache is often the first symptom of both dehydration and hyponatremia. So athletes may confuse them. When you’re working out and feel a headache coming on, you may drink water when in fact overhydrating is what caused the headache in the first place. Drinking more water just makes it worse.[xii]
If you’re not sure whether you’re drinking too much or too little during exercise, try weighing yourself before and after a workout.
If you have lost more than about 3% of your body weight (5-½ pounds if you weigh 180, 4 pounds if weigh 140), you’re flirting with dehydration. Drink more next time.
But if you have gained weight or your fingers seem swollen and your rings are tight after a workout, you’re most likely drinking too much.
Most importantly, listen to your body, Dr. Rosner said. “Thirst is a very reliable indicator,” he said.[xiii]
Does drinking more water stop your body from mistaking thirst for hunger?
Dr. Stephan Guyenet is an obesity researcher and author of the book Hungry Brain. He said there is no research showing that people mistake thirst for hunger. “I’m not aware of any evidence that’s the case,” he said.[xiv]
Hunger and thirst signals operate on different biological systems, said Dr. Barbara Rolls of Pennsylvania State University. That makes it unlikely that you would confuse one for the other, she said.[xv]
But that hasn’t stopped the myth from perpetuating. “You see it all the time in tips for dieters: ‘You may be eating because you are thirsty, not hungry,’” Dr. Rolls said.
It is true that drinking fluids can make you feel fuller, she said. “When you drink something, the brain receives messages that something has entered your stomach, and this can provide a temporary reduction in hunger that passes quickly,” she said. “But this has nothing to do with feeling thirsty and interpreting that as feeling hungry.”
A study published in the journal Physiology & Behavior debunked the idea that people mistake thirst for hunger.[xvi]
Scientists at Purdue University asked subjects to rate their feelings of hunger and thirst every hour. At the same time, researchers measured their hydration levels and tracked the amount of food in their systems.
Scientists found that when subjects’ hydration levels were low and food levels high, they virtually always reported feeling thirsty—not hungry.
The One Simple Rule of Hydration
When it comes to hydration, the bottom line is simple: “Drink when you are actually thirsty,” said Dr. Carroll.
Dr. Brad L. Bennett, who advises the military on fitness matters, said that over-hydration is a health issue that flies under the radar.
“Even after 40 years of worldwide documentation of hyponatremia, there is still an ongoing need for education,” he said. “People should drink enough to satisfy their thirst, but avoid overdrinking.”[xvii]
Editor’s Note: Unlike much of the mainstream media, we don’t accept advertising from Big Pharma. That’s why you can count on us for unbiased medical information. Our only motivation is your good health.
Our monthly journal Independent Healing brings you important, science-based health news you won’t find anywhere else. To subscribe, go HERE.