Healthy people do not need eight 8oz glasses of water a day
"You need to drink eight to ten glasses of water per day to be healthy" is one of our more widely-known basic health tips.
But do we really need to drink that much water on a daily basis?
The recommendation to drink six to eight glasses of water a day to prevent dehydration "is not only nonsense, but is thoroughly debunked nonsense," argues Margaret McCartney in in the July 12, 2011 online edition of the British Medical Journal, argued
“There is currently no high quality published evidence of benefit from drinking increased amounts of water.”
The British National Health Service (NHS) Choices website states: "Try to drink about six to eight glasses of water (or other fluids) a day to prevent dehydration," while many schools also feel it appropriate to insist that pupils are accompanied to school by a water bottle.
Other organisations, often with vested interests, reinforce this message, she says. For example, Hydration for Health (created by French food giant Danone -- makers of bottled waters including Volvic and Evian) recommends 1.5 to 2 litres of water daily as "the simplest and healthiest hydration advice you can give." It also claims that "even mild dehydration plays a role in the development of various diseases."
She points to several studies showing no clear evidence of benefit from drinking increased amounts of water and suggesting there may be unintended harms attached to an enforcement to drink more water.
"It would seem, therefore, that water is not a simple solution to multiple health problems," she writes.
For instance, reports that increased water intake in children can improve concentration and mental performance have not been confirmed by research studies, while data relating water drinking to a reduction in children being overweight are prone to bias.
While there are some conditions that do benefit from drinking increased water, such as in people with recurrent kidney stones, other evidence for preventing disease is conflicting, adds McCartney. In other words, this is a complex situation not easily remedied by telling everyone to drink more.
Untangling the evidence presented by Danone "results in weak and biased selection of evidence," she argues. Danone says we need "informed choices," but their own evidence does not support their call to action.
She concludes: "There are many organisations with vested interests who would like to tell doctors and patients what to do. We should just say no."
M. McCartney. Waterlogged? BMJ, 2011; 343 (jul12 2): d4280 DOI: 10.1136/bmj.d4280
So how much water do you need?
As long as you are healthy and equipped with a thirst barometer unimpaired by old age or mind-altering drugs, follow Joseph Verbalis's advice, "drink to your thirst. It's the best indicator."
Joseph G. Verbalis, MD is Professor of Medicine and Physiology and Chief of the Division on Endocrinology and Metabolism at Georgetown University.
Drinking Too Much Water Can Kill
“In a hydration-obsessed culture, people can and do drink themselves to death,” Coco Ballantyne, wrote in Scientific Amercian, June 21, 2007. CLICK HERE for details.