Eight glasses of water a day keep the doctor away, some say, or at least improve skin tone, remove toxins from the body, prevent migraine headaches and suppress appetite. Nonsense, says Stanley Goldfarb, a kidney expert at Penn. “There [is] no evidence to say that drinking this extra water really [does] you any good.”
Goldfarb and Dan Negoianu, both of the Renal, Electrolyte and Hypertension Division at HUP, performed a study to determine if there is any real scientific evidence to prove the alleged benefits of increased water consumption. In nearly all cases, the answer was no.
Short of being outside on a hot day or exercising during the summer, “the need for extra water is really just not something that one would expect because the kidney rapidly excretes any extra water when it gets into the system,” Goldfarb says. “The biology that we understood would suggest that it’s unlikely there was a benefit, and then when people actually went to study it, there was no evidence of a benefit.”
Goldfarb and Negoianu also sought to dispel “wives’ tales,” some stretching back to the late 18th century, that claim increased water intake leads to healthy skin, a cleansed, migraine-free body and decreased appetite.
“When you drink water, it distributes throughout your body,” Goldfarb says. “It goes into every cell in the body, it doesn’t just go to one place or another in the body.” If water does influence a person’s skin, it doesn’t just influence the skin on his or her face, which he says is a person’s main concern.
The human body, Goldfarb says, is designed to dispose of toxins via the liver and kidneys, and does so effectively.
“The way the kidney works is to filter the blood, and it filters the blood almost unrelated to how much fluid is in the system,” he says. “It filters the blood in a pretty constant way, assuming that you aren’t at the extremes of not enough water in your system…But with the normal amount [of water] in your system, adding a little bit of water isn’t going to change the way your kidney filters the blood.”
In fact, Goldfarb says increased water intake may, for unknown reasons, slightly lower the efficiency of filtration.
A person suffering from severe dehydration, such as someone crossing the desert, may get a migraine headache as part of being very ill, but otherwise Goldfarb says there is no evidence to prove that drinking water can reduce migraines. “So that’s another one of those wives’ tales,” he says.
Many diet books advocate drinking water to reduce appetite, specifically before eating a meal. While it is apparently true that drinking a lot of water immediately before a meal can fill up the stomach to some degree, Goldfarb says drinking extra water during a meal doesn’t suppress appetite or caloric intake and no one has ever shown that drinking excess water will actually produce weight loss.
Goldfarb says all these issues need to be studied more because there’s very little good information. Someone could do a study “next week or next year or next month” to find a benefit. And there are no negatives to drinking extra water (except water intoxication). But, he says, just because more information is needed doesn’t mean there’s a good scientific basis for the water claims.
The moral of the story, says Goldfarb, is “drink (any liquid) when you’re thirsty.” People with kidney, liver or heart disease may need increased water intake, or soldiers fighting in Iraq or Afghanistan, but he says even someone with only one kidney doesn’t need to drink extra water.
Originally published April 24, 2008.
