July 13, 2011

Do We Really Need 8 Glasses Of Water Per Day?

The long-time recommendations to drink six to eight glasses of water per day to prevent dehydration "is not only nonsense, but is thoroughly debunked nonsense," according to a doctor writing in the British Medical Journal on Tuesday.

Dr. Margaret McCartney, a general practitioner from Glasgow, Scotland, argues that there is no clear evidence of benefit from drinking increased amounts of water, yet the "we-don't-drink-enough-water" myth has endless advocates, including those from the National Health Service (NHS).

The NHS Choices website states: "Try to drink about six to eight glasses of water (or other fluids) a day to prevent dehydration." And many schools get so hung up on the advice, they feel it's appropriate to insist that pupils carry a bottle of water to school with them.

Also, many physicians will tell their patients to drink up to eight glasses of water per day, even though there is no actual research suggesting why this amount should be the norm. For your skin, for your weight, for your kidneys -- such advice has been passed around for years, along with the phrase: "drink more water, it's good for you."

But why? This is the question that some medical groups have been pondering over for the past few years now. Their argument is this: there's no evidence that drinking more water helps our health, so shouldn't we just drink when we're thirsty?

That's the message Dr. McCartney is putting forth in her published article.

McCartney said that in 2002 Professor Heinz Valtin, from Dartmouth Medical School in the US, published a review of the evidence in the American Journal of Physiology concluding there was no real "scientific evidence that we need to drink that much" water.

Unsurprisingly, bottled water companies were keen to push the advice as a public health message.

Groupe Danone, a French-based food company behind the Volvic and Evian water brands, recommends drinking up to two liters (eight standard glasses) of water daily as "the simplest and healthiest hydration advice you can give."

The company also claims that "even mild dehydration plays a role in the development of various diseases."

David Graham, director of Danone's Hydration for Health initiative said: "Our view on how much water you should drink is in line with the European Food Safety Authority's 2010 scientific opinion on water intake."

"The amount a person should drink is dependent on personal factors, such as sex and age, and EFSA's opinion to drink 1.5l to two liters of water per day is sensible for a normal woman or man," he wrote.

However, McCartney wrote that there was no real evidence to support Danone's claim.

She pointed to several studies showing no clear evidence of benefit from drinking increased amounts of water and suggesting there may be unintended harm attached to an enforcement to drink more water.

"It would seem, therefore, that water is not a simple solution to multiple health problems," she wrote.

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, she adds.

McCartney argues that Danone's evidence is "weak and biased." The company says we need "informed choices," but their own evidence does not support their call to action.

She remains up in arms about the whole situation.

"We can emphasize non-evidenced based things too much," she told ABCnews.com, which detracts from the real health messages we should be sending about exercise diet, and not smoking.

McCartney isn't the first person to debunk the water myth. In 2008, Dr. Stanley Goldfarb, a nephrologist at the University of Pennsylvania Perelman School of Medicine, and colleagues tackled several common water myths that had been circulating around the Internet.

"We found that there really is no evidence that drinking more water makes you perform better. It doesn't reduce appetite, it doesn't lead to long-term weight loss, and it can't possibly improve your complexion. It won't clear your body of toxins or reduce headaches," Goldfarb told ABCnews.com.

"There's just no basis for these contentions," he said.

Goldfarb said he would find himself arguing with those who didn't want to accept that drinking lots of water didn't seem to provide any health benefits.

He attributed some of the persistence of water myths to the fact that many physicians will back the urge to drink plenty of water because "it really can't hurt you" and it's a "free, easy health message to give." After all, what's the harm in drinking more water than you need?

Both McCartney and Goldfarb agree that the answer is: not much. Drink too much water (as long as it is not an extremely large amount of water) and you will just pee it out.

The real harm, McCartney argues, is when the call to "drink more water" becomes the marketing call to "drink more bottled water." The US consumes more than 8 billion gallons of bottled water annually, up from 5 billion in 2001, according to the International Bottled Water Association.

"The notion that you have to drink water from Fiji is insane. That's part of America -- people are taken in by marketing issues," said Goldfarb.

And "what about all the plastic bottles, the transport of water round the country, and subsequent environmental harm?" said McCartney.

The real message is simple: dehydration is bad, but if you are in good health and drinking when you are thirsty, you're probably fine.

"Thirst is a highly developed sensation, powerfully motivated. When you're thirsty, all you want to do is drink. But being thirsty doesn't mean you are ill at this point or dehydrated to the point that there are consequences," said Goldfarb.

Another measure: Watch the color of your urine, said Dr. Randy Wexler, a physician and assistant professor at Ohio State University. "The more clear the urine, the better the hydration. The darker, the more dehydrated." 


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