Benefits of Drinking Water Oversold?
Researchers Say Evidence Is Lacking for Benefits of Drinking 8 Glasses of Water a Day
WebMD News Archive
Claim No. 1: Drinking Water Helps Excrete Toxins
Drinking lots of water is widely thought to help improve kidney function and
boost the clearance of toxins. One way it could do this, Goldfarb says, is by a
mechanism called glomerular filtration, a measure of the kidney's ability to
filter and remove waste products.
But in one study the researchers looked at, increased water intake by 12
young and healthy people actually decreased their glomerular filtration
rate. And in another study, the rate did not change over time during a
six-month period in which older men drank more water to try to improve bladder
In other research, increased water intake was found to affect the clearance
of many substances by the kidneys, including sodium. But the studies don't
prove any sort of clinical benefit, Goldfarb says.
"What almost certainly happens is, any toxins the kidney is responsible
for excreting simply get diluted when the person is drinking a lot of
water," Goldfarb says.
Claim No. 2: Drinking Water Helps Your Organs Work Better
Water is retained in various organs, so the thinking goes, and they work
better with more water in them.
But Goldfarb and Negoianu say how much water is retained varies with the
speed with which the water is taken in. If it's sipped, it's more likely to
stay in the body than when gulped.
Even so, they could find no studies documenting that increased water intake
helped the organs.
Claim No. 3: Drinking Water Reduces Food Intake and Helps You Lose Weight
Drinking more water is widely encouraged to help weight loss, the theory
being that the more water you drink, the fuller you will feel and the less you
will eat. "The [medical] literature on this is quite conflicted,"
"Drinking before a meal might decrease intake [according to one study],
but another study found [it did] not."
Even so, Goldfarb calls this claim one of the most promising for further
Claim No. 4: Drinking Water Improves Skin Tone
"From a quantitative sense, this doesn't make sense," Goldfarb says.
The water you drink will be distributed throughout the body. "Such a tiny
part of it would end up in the skin," he says.
"It turns out one small study showed there might be an increase in blood
flow in those who drink [a lot of] water, but no one has ever looked
scientifically [to see if it improves skin tone]."
Claim No. 5: Drinking Water Wards Off Headaches
Headache sufferers often blame water deprivation. But Goldfarb could only
find one study that looked at this. The study participants who boosted their
water intake had fewer headaches than those who did not, but the results were
not statistically significant, meaning they could have been chance