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8x8 study prompts a deluge in the press (as well as in puns)

The "Media Mentions" section of this magazine (see page 18) couldn't begin to contain the recent deluge of press coverage provoked by Heinz Valtin, M.D., a kidney specialist and the Vail and Hampers Professor Emeritus of Physiology at DMS.

A Wall Street Journal story in May leaked word of an article that Valtin was working on (titled "Drink at Least Eight Glasses of Water a Day—Really? Is There Scientific Evidence for '8x8'?") prior to its scheduled online publication by the American Journal of Physiology (AJP).

Outlets: Suddenly, reporters from all over the country and the world—and from media outlets as diverse as the Dallas Morning News, Yahoo! News, and National Public Radio's Morning Edition—were clamoring for interviews. "I'm ready for it to be over," says the normally buoyant Valtin with a perceptible sigh.

Dartmouth physiologist Heinz Valtin has been inundated with e-mails and phone calls from reporters all over the world, ever since the online release of a review article he was invited to write on the scientific justification (or lack thereof, as it turns out) for the recommendation to drink at least eight 8-ounce glasses of water a day.
Image: Matthew Myers

Why all the fuss? Valtin's review article, undertaken at the invitation of the AJP, found no evidence to support the vigorously promoted assertion that drinking at least eight 8-ounce glasses of water a day (known as the "8x8" rule) is essential to good health.

Not only did Valtin not find any benefit in following the supposed rule for healthy, mostly sedentary people in a temperate climate—the vast majority of 8x8 proponents—but he noted that, in some cases, drinking too much water can cause harm.

Nevertheless, devoted waterdrinkers were incensed by the mere mention of his study, as reporter Lini Kadaba discovered when she interviewed a few for the Philadelphia Inquirer. "I don't believe it," said one fitness trainer when Kadaba asked him about Valtin's article. He wasn't planning to cut back on his consumption, usually a gallon a day, nor were any of the other waterbottle- toting Philadelphians whom Kadaba spoke with.

Those who never took to water in a big way are delighted, of course; now they can stop feeling guilty in the presence of their constantly sipping brethren. Some, such as Wall Street Journal reporter Betsy McKay, suggested it's the bottled-water industry that promotes 8x8. "We may not be as dehydrated as bottled-water makers would have us believe," McKay wrote.

Given the strong feelings on both sides of the water issue, as well as the suspicion that marketers are creating "health information"— not to mention the plethora of punning opportunities inherent in the topic—it's no wonder the media has waded in so gleefully.

Ruckus: Heinz Valtin, meanwhile, says that he had no intention of causing such a ruckus. About a year ago, motivated by skepticism in the medical community and uncertain of the origin of 8x8, the AJP editors asked Valtin to do a thorough review of the literature to determine if there was any scientific justification for drinking so much water. Valtin, the author of three textbooks on the kidneys and water balance and a researcher in the field for more than 40 years, was a natural choice. Enlisting the assistance of Dartmouth biomedical librarian Sheila Gorman, he undertook a 10-month survey of the scientific literature— and came up dry.

"I want to emphasize that I found no scientific evidence to back up 8x8," Valtin says. "I'm talking about randomized trials published in peer-reviewed journals." Nor did he find a definitive origin for the 8x8 recommendation, though he suspects a misreading of a 1945 federal report. That report said people need about 64 ounces of fluids a day, adding that much of it is contained in food—a caveat Valtin believes was overlooked.

A high water intake does benefit certain people, such as those who suffer from kidney stones or who work or exercise outdoors on a hot day. "The problem is that it's a universal recommendation," Valtin says, "and I want people to be aware that plain water can be harmful, or even fatal." Under certain circumstances, excess fluids can cause water intoxication, a condition that occurs when the kidneys cannot keep pace with water intake. The body retains water, diluting solutes in the blood and causing cells to swell. When brain cells swell, the result is mental disorientation, followed by seizures and even death.

Valtin's article cites several cases of hyponatremia, or water intoxication, among them a 16- year-old girl taking the drug Ecstasy for the first time. The drug, which produces intense thirst, apparently interfered with her normal kidney function.

Water intoxication can also occur in diabetic patients taking certain medications and is being reported with increasing frequency among endurance athletes. Though such cases are not common, they refute the assumption that drinking excess water is harmless.

In the absence of disease or other interference with the osmoregulatory system, the body maintains water balance either by releasing antidiuretic hormone (ADH) or by producing thirst. This finely tuned system can also slow down evaporation through the skin and signal the kidneys to release water back into the body when needed. "The body's own system is quick to restore water balance in healthy persons," Valtin says, noting that (also contrary to myth) thirst occurs before the onset of dehydration.

Further annoying 8x8 adherents, Valtin presented evidence that juice, milk, and even caffeinated beverages and beer—in moderation—can be sources of fluid intake. When these beverages are counted, Valtin says, the average daily intake for adult Americans is 1,700 milliliters, just shy of the 8x8 water-only target of 1,900 milliliters. And that average doesn't include the water content in fruits, vegetables, and other solid foods.

"I would argue that for the time being, the burden of proof that everyone needs 8x8 should fall on those who persist in advocating the high fluid intake without, apparently, citing any scientific support," Valtin concludes. Except under special circumstances, he maintains, "we probably are currently drinking enough and possibly more than enough."

Tide: By November, when the AJP is scheduled to publish his article in its print edition, Valtin —who has encouraged anyone with good data supporting 8x8 to come forward—will probably be more than ready to see the tide of questions stemmed.

Catherine Tudish

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