Drink More Water? Just Say No, Doc Says
Published: Jul 12, 2011
By Kristina Fiore, Staff Writer, MedPage Today
The need to drink eight glasses of water a day may be as big a myth as the fountain of youth, according to one U.K. physician.
Several studies have found no evidence of benefit for recommending such levels of hydration, although bottled water companies would have consumers believe otherwise, argues Margaret McCartney, MD, of Glasgow, Scotland, in a commentary in BMJ.
"There are many organizations with vested interests who would like to tell doctors and patients what to do," McCartney wrote. "We should just say no."
The recommendation to drink eight glasses of water a day (at eight ounces each) has become a standard for healthy hydration. It's the level recommended by Britain's National Health Service, and the U.S. Institute of Medicine (IOM) in 2004 found that "adequately hydrated" women consumed 91 ounces of water a day, and men had 125 ounces -- almost 16 glasses.
However, those amounts can come from coffee, tea, milk, soda, juice, fruits, vegetables and other juicy foods, and ultimately the IOM recommends that thirst should be a patient's guide to intake.
But in a brief literature review, McCartney found several studies showing no clear evidence of benefit for such levels of hydration.
A 2002 study by Heinz Valtin, MD, published in the American Journal of Physiology, for instance, concluded that there's "no scientific evidence that we need to drink that much," and those levels may even be harmful, resulting in hyponatremia and exposure to pollutants.
A 2008 editorial in the Journal of the American Society of Nephrology noted that while there's no clear evidence of benefit, there's "no clear evidence of lack of benefit" either -- thus, a "lack of evidence in general."
Studies cited by hydration advocacy groups such as Hydration for Health, which is sponsored and created by the French food giant Danone (maker of Evian, Volvic, and Badoit bottled waters), are limited, McCartney says -- they're either retrospective studies with methodological limitations or based on low-quality guideline recommendations.
More recently, the organization promoted a claim that hydration prevents chronic kidney disease, but McCartney argued that is supported merely by one cross-sectional study recently published in Nephrology.
"Examination of the evidence presented by Danone shows it to be weak and subject to selection bias," she wrote. "Danone says we need 'informed choices,' but its evidence does not support its call to action."
Stanley Goldfarb, MD, of the University of Pennsylvania, who was interviewed by McCartney, told ABC News and MedPage Today that "there's just no evidence for keeping yourself hydrated above and beyond the need to avoid thirst."
"There really is no evidence that it makes you perform better, it doesn't reduce appetite, it doesn't lead to long-term weight loss, it can't possibly improve your complexion," he said. "But many physicians still recommend it, I think, because it really can't hurt you."
Randy Wexler, MD, professor of family medicine at Ohio State University, said he tells patients simply to remain adequately hydrated, via any means necessary: "There's no evidence I am aware of that says it must be water."
Yet he tells those prone to dehydration, especially the elderly, to avoid caffeinated beverages that can cause over-diuresis.
And because he says all patients have different "thirst sensors," he advises that they monitor the color of their urine to gauge their dehydration instead.
"The more clear the urine, the better the hydration," he said in an email to MedPage Today and ABC News. "The darker, more yellow the urine, the more dehydrated one is."
This article was developed in collaboration with ABC News.