If there’s one health recommendation that everyone seems to know, it would probably be to drink eight glasses of water a day, which is also known as the “8×8” rule. It sounds logical enough: Since our bodies need water to function, not drinking enough of it prevents us from functioning optimally. But is there really something to drinking eight eight-ounce glasses of water daily or is it just a bunch of hogwash?
Many people are convinced that they’re in a perpetual state of dehydration and are concerned about falling short of the 8×8 rule. Of course, there are plenty of reasons why we may think we’re falling short—forgetting to drink because of a busy schedule, not adequately rehydrating after workouts, drinking too much caffeine, or substituting other beverages for water, for example. And for the average person, drinking eight glasses of water a day requires dedicated effort.
The reality is that most people actually consume plenty of water each day, just not in the form of pure water. When considering total water intake, all forms of common beverages — such as water, coffee, tea, soda, and juice — help keep us very well-hydrated. Also, the moisture content in the foods we consume contributes significantly to our daily total water intake.
Where did the eight-glasses-of-water-a-day rule come from?
This 8×8 rule likely originated from a misinterpretation of an outdated recommendation from 1945 when the Food and Nutrition Board — now part of the Institute of Medicine (IOM) — suggested that a person consume one milliliter (ml) of water per each calorie of food consumed. Thus, an average diet of 1,900 calories per day would dictate an intake of 1,900 ml (approximately 64 ounces) of water. However, people interpreted this as a recommendation to drink 1,900 ml of pure water, forgetting the fact that water is also found in abundance in the other liquids and foods we consume.
So how much water should I really drink?
Today, the IOM liberally recommends an even higher volume of total daily water intake: 3.7 liters (15 cups) for the average adult male and 2.7 liters (11 cups) for the average adult female. If these numbers seem daunting, don’t worry. Keep in mind that water needs vary tremendously by individual, and are dependent on numerous factors such as activity level, geographic location, and temperature. In fact, most people will be adequately hydrated at levels well below these recommended volumes. But, are there, in fact, health benefits to drinking this much water? Not according to the latest research. A 2002 study published in the American Journal of Physiology and a 2008 study from the Journal of the American Society of Nephrology demonstrated no significant health benefit of the 8×8 rule. However, adequate water intake is still necessary for maintenance of bodily functions.
So how do you know whether your body is properly hydrated? Rather than religiously documenting every ounce of fluid intake, the IOM advises drinking liquids with your meals and to make sure you heed your body’s request for water by drinking when you feel thirsty. This, under most circumstances, will provide you with your daily water needs. Most people without specific health concerns will be able to maintain good hydration by following this advice. Now, whether your drink of choice is a healthy one is a whole other discussion.
The One Medical blog is published by One Medical, an innovative primary care practice with offices in Boston, Chicago, Los Angeles, New York, Phoenix, the San Francisco Bay Area, Seattle, and Washington, DC.
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