Eight glasses a day may be unnecessaryby Heather MurphyPublic Relations You see them everywhere. Dangling by straps or toted by hand, bottled water is a staple of the modern student's and professional’s daily attire. Seeing so much bottled water and a slew of Web sites promoting the drinking of water begs the question, why is everyone so concerned with drinking water? The time-honored phrase has been “drink at least eight 8 oz. glasses of water a day.” A distinguished faculty member of Dartmouth Medical School, Heinz Valtin, M.D., believes that humans don’t need that much water on a daily basis. Valtin, described by MUSC nephrologist David Ploth, M.D., as a world class expert in water metabolism, published a review in the American Journal of Physiology stating there’s no evidence to support the eight by eight claim. “I never understood myself where the claim came from. Eight glasses or more of water every day seems like it would stress the system,” said Ploth. Valtin sought out scientific evidence to support the eight by eight rule but seriously doubted its validity. “It’s difficult to believe that evolution left us with a chronic water deficit that needs to be compensated by forcing high fluid intake,” he said. Valtin believes the idea originated when the Food and Nutrition Board of National Research Council recommended in 1945 approximately “1 milliliter of water for each calorie of food,” which amounts to roughly 64 to 80 ounces of water a day. But the next sentence says, “most of this quantity is contained in prepared foods.” Several published studies, he says, go as far to say that caffinated drinks may even be counted towards the daily total of water intake and other studies support the capability of the human body to maintain proper water balance. That being said, it seems a bit extreme that the body needs at least 64 ounces of daily water intake from liquid water, food and other beverages plus an additional 64 ounces of liquid water. Why should you drink more if you’re already getting what you need? “Eight glasses of water is probably more than is needed,” said Stephanie Tranen, director of the Dietic Internship. “But there really is no disadvantage in drinking eight glasses of water if your kidneys are functioning properly,” she said. And Valtin agrees that certain medical conditions require an increased water intake, “Large intakes of fluid are advisable for the treatment or prevention of kidney stones and are also needed in special circumstances like strenuous physical activity, long airplane flights, or hot weather.” Valtin claims there’s possible danger in too much water. “Even moderate increases in fluid intake can result in water intoxication if one’s kidneys can’t excrete enough water (urine).” While Valtin worries that too much water may lead to water intoxication and other disadvantages like exposure to pollutants, frequent urination, and expense if you drink bottled water, Tranen believes that what he refers to as disadvantages are not really that prevalent and that the real problem is becoming dehydrated. As far as her thoughts on the eight by eight rule, Tranen said, “It’s as good a number as any other and it seems to work for those that choose to drink that much water. I’d venture to say that there isn’t too much to worry about because most people don’t drink that amount or more anyway.” Ploth believes that thirst is always a good indicator of whether or not your body needs fluid. “Thirst begins when the concentration of blood has risen by less than two percent whereas most experts define the beginning of dehydration as the concentration rising by at least five percent,” Valtin said. With all of this in mind, how much water do individuals need? Valtin, Ploth and Tranen all agree that different individuals need different average water intakes dependent on diet, amount of exercise, and the presence of medical conditions. Tranen finds the eight by eight rule and it’s connection to the bottled water industry “amusing.” “Ten years ago nobody carried water bottles around or was very concerned about water intake. People are drinking water heavily because of clever marketing,” she said, “There’s a whole isle of water at the grocery store. It’s interesting to think that the whole bottled water industry may be partially based on the eight by eight rule, and that rule may not be correct.” Thinking it out:
Average person’s approximate daily water intake:
Approximate daily water loss:
Don’t believe everything on the Internet…
If a 120 lb. person needs to do the “minimum” for water replacement, according to this Web site, then that person needs half of his or her body weight, 60, in ounces of water. It then tells you that for better results, you should triple that intake to 180 oz. That’s a 120 person drinking 22.5 8 oz. glasses of water every day to replace a little more than the bare “minimum” of daily water loss. If this were truly the case, we’d never leave the bathroom.
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