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Drink Eight Glasses of Water A Day?

By Andrea Pennington, M.D.

You've heard it everywhere — your doctor, your mum, nutritionists, fitness experts — drink eight 8-ounce glasses of water every day for good health. I admit to admonishing my patients to do so. And I previously carried around a water bottle religiously.

But, no more. Many of my colleagues at Discovery Health have questioned whether we really need to drink so much water. Well, a new medical review shows that we probably do NOT.

In a review published online by the American Journal of Physiology a Dartmouth professor concludes that he can find no supporting evidence to back the popular advice, commonly known as "8 x 8" (for eight, eight-ounce glasses).

Dr. Heinz Valtin, a kidney specialist and author of two widely used textbooks on the kidney and water balance, doesn't believe that humans exist in a constant water deficit necessitating the constant imbibing of H2O.

Valtin thinks the notion may have started when the Food and Nutrition Board of the National Research Council recommended approximately "1 milliliter of water for each calorie of food (consumed)," which would amount to roughly two to two-and-a-half quarts per day (64 to 80 ounces). This was interpreted as how much water one should drink each day.

What Valtin thinks the world has missed follows in the last sentence of that statement by the Board. "Most of this quantity is contained in prepared foods."

In his review, Dr. Valtin also found no scientific studies in support of 8 x 8. In fact, most studies of fluid intake in healthy adults strongly suggest that such large amounts are not needed. He also points to the quantity of published experiments that attest to the capability of the human body for maintaining proper water balance.

More than just water

I used to ask my mother, also a physician why she didn't drink more water Her reply, "well, there's water in coffee and juice..." And, my mother was right. Dr. Valtin affirms that we can count the water other liquids toward our daily 'needs.' Careful peer-reviewed experiments have shown that caffeinated drinks should indeed count toward the daily fluid intake in the vast majority of persons.

At the time, we thought he was crazy, but this further explains why the renal pahtophysiology professor* at my medical school drank at least two diet cokes in each lecture! Caffeine addiction notwithstanding. (*Renal pathophysiology is the study of disease processes of the kidney.)

Dr Valtin does stress that large intakes of fluid, equal to and greater than 8 x 8, are advisable for the treatment or prevention of some diseases, such as kidney stones, as well as under special circumstances, such as strenuous physical activity, long airplane flights or hot weather. But barring those exceptions, he concludes that we are currently drinking enough and possibly even more than enough.

Enough is Enough

As has been pointed out in the media, you can actually drink too much water and cause health problems, even death. "Water intoxication" can occur if one's kidneys are unable to excrete enough water (urine). Such instances are not unheard of, and they have led to mental confusion and even death in athletes, in teenagers after ingesting the recreational drug Ecstasy, and in ordinary patients.

So, the bottom line is: Drink when you're thirsty. Anticipate when you may end up requiring additional fluid intake, such as with outdoor sports in hot weather, strenuous exercise and certain medical conditions.

When the heat index is high, stay indoors in air-conditioned areas when possible to prevent heat related illness.

Be Well, Andrea Pennington, MD