MSN Health & Fitness
Turbulent Waters
By Allison J. Cleary, EatingWell.com
MSN Health & Fitness
Turbulent Waters
By Allison J. Cleary, EatingWell.com
They’re everywhere. Bottles of water have become near-fashion statements for the nutritionally hip, sloshing about in the hands of college students, mall shoppers, office workers and joggers. From construction site to corporate boardroom, we sip them throughout the day, urged on by health-care professionals, parents and teachers to drink more. In the unsettled rivers of nutrition advice, at least one message has run strong for decades: drink eight 8-ounce glasses of water every day or risk the consequences of neglected health. But recent studies question just how much water we really need each day.
For years, says Heinz Valtin, a kidney specialist at Dartmouth Medical School, he and colleagues who specialize in the field of water balance have suspected that the recommendation to drink 64 ounces of water a day (also called the “8-by-8” rule) might lack proof. So when The American Journal of Physiology invited him to review the scientific literature for evidence that supports the claim, Valtin began a 10-month search that came up empty.
“I have found absolutely no scientific evidence that supports the recommendation that everyone drink at least eight 8-ounce glasses of water a day to promote health and avoid dehydration,” Valtin writes.
For some people who have found the two-quart advice difficult to swallow, the news may come as a relief, to their bladders at the very least. Valtin suggests that for the average healthy adult, living in a temperate climate and leading a sedentary existence—working in an office, for example—between six and seven 8-ounce glasses of fluid are probably enough.
Not everyone in the medical establishment agrees. Jacqueline Chan, a researcher on the Adventist Health Study, tracked the health and lifestyles of more than 20,000 Seventh-Day Adventists in California and found that the more water a person drinks, the more likely he or she will avoid fatal heart attacks.
“Men drinking five or more glasses of water a day can reduce their risk of a fatal heart attack by 50 percent. That’s as much as stopping smoking,” Chan marvels.
Chan suspects that the protection water seems to provide may be related to blood viscosity, essentially how thick it is. She postulates that a man who drinks five or more glasses of water per day will have much thinner blood than the average man who drinks only 2.8 glasses of water, the comparison figure.
“Higher blood viscosity increases damage to the inner lining of the blood vessels,” Chan explains. “The more damaged the arteries, the narrower they become and the chance of clotting increases.” Heart attacks are the result of clots that can block the flow of blood to the heart.
For women, the risk reduction from water was slightly less dramatic but still significant at 40 percent. That may be because women, whose blood cells bend more easily, generally have a lower blood viscosity than males, Chan says. “And we don’t sweat as much as men so we don’t lose water as quickly,” she adds.
Valtin, who reviewed Chan’s study favorably, says she and her colleagues offer a reasonable explanation for the correlation they found between water intake and heart problems, but points out that the benefits were seen with as few as five glasses a day, considerably less than the 8-by-8 rule.
But Chan believes that the protection would increase with even more water. Unfortunately, the low number of people drinking eight or more glasses of water among the 20,000 Adventists studied was not significant enough to provide statistically convincing results.
The two scientists also differ on the type of fluid that counts. “By and large, the six to seven glasses I speak of to maintain water balance can include beverages other than water, such as coffee, tea, soft drinks, even beer in moderation,” Valtin concludes. But Chan’s analysis showed that women who drank five or more glasses of fluids instead of water—milk, caffeinated beverages, juices or sodas—were more than twice as likely to suffer a fatal heart attack than those who stuck to water. So convincing were the results that Chan says, “I can’t believe that water isn’t in the food pyramid.”
If you choose to follow the 8-by-8 rule, the challenge lies in how to succeed in filling up. “You have to do more than sip,” Chan says. At the beginning of the work day, she fills a glass jug with 48 ounces of water and makes sure that she has finished drinking it by day’s end. “I get distracted by my work and I won’t take the time to walk down the hall to the water fountain.” At home she makes sure that she adds a glass of water to the equation in the morning and evening.
In his survey of the literature, Valtin points to studies that correlate higher fluid intakes—six glasses and more— with lower incidences of bladder and colorectal cancer, urinary tract infections and kidney stones. He also stresses that strenuous physical activity, long airplane flights, hot weather and certain diseases increase the human body’s need for water.
However, he argues that most of us “are probably drinking enough,” and says that the burden of proof for the health benefits of drinking more than six glasses of fluid per day is now on those who recommend the 8-by-8 water regimen.
Chan, on the other hand, asserts that all those daylong water quaffers are making the right choice in replacing caffeinated, sweetened and alcoholic fluids with pure water.