DRINK AT LEAST EIGHT GLASSES OF WATER A DAY FOR BETTER HEALTH?

This age-old advice is the scientific equivalent of an “urban legend,” with no basis in fact, according to a noted Dartmouth researcher whose findings are published in the American Journal of Physiology

August 12, 2002  -  (Bethesda, MD)  --  Fashion magazines, diet gurus and grandmothers have one thing in common: they each recommend we drink at least eight 8-ounce glasses of water a day.  A just released literature review by a noted Dartmouth physiologist, however, has found no scientific basis for this age-old wisdom.  

Heinz Valtin, M.D., a kidney specialist and professor emeritus of physiology at Dartmouth Medical School, Hanover, NH, has published a literature review on the subject in the upcoming edition of the American Journal of Physiology: Regulatory, Integrative and Comparative Physiology.  The article, being published in hardbound format later this year, was released online today by the journal’s publisher, the American Physiological Society (APS), to its “Article In PresS^®” section.

Key Findings of the “8x8” Review

Dr. Valtin set out to find the origin of the recommendation, “drink at least eight 8-ounce glasses of water a day” (“8 x 8” as it is also known), and for its accompanying guidance that prohibits consumption of caffeine products or alcoholic beverages from being counted toward the goal.  As a consequence of his investigation he determined that:

• He could find no scientific evidence to support the 8 x 8 water intake recommendation.

• Surveys of food and fluid intake conducted on thousands of adults of both genders suggest that such a large amount is unnecessary, because those surveyed were presumably healthy and not overtly ill.

• Caffeinated drinks, and to a lesser extent dilute alcoholic beverages such as beer taken in moderation, may indeed be counted towards an 8 x 8 goal.

Dr. Valtin emphasizes that these conclusions apply to healthy adults in a temperate climate, leading a largely sedentary existence.  He stresses that consumption of 8 x 8 or more is, indeed, advisable and needed for the treatment and prevention of some diseases, and is, of course, called for under special circumstances such as strenuous physical work or exercise, especially in hot climates.

How Did the National Habit of “8x8” Get Started?

How did the national habit get started? No one knows.  Dr. Valtin thinks that 8 x 8 may stem from guidelines posted by the Food and Nutrition Board of the National Research Council (NRC):

"An ordinary standard for diverse persons is 1 milliliter for each calorie of food.  Most of this quantity is contained in prepared foods."

The second sentence may have been forgotten or not heeded, so that the NRC's guideline was erroneously interpreted as eight glasses of water to be drunk each day.  The Food and Nutrition Board is currently re-evaluating its recommendation.

Should Caffeine Be Counted Towards the 8x8 Consumption Goal?

According to Valtin, there is strong scientific evidence that not all of the 8x8 needs to be taken in the form of plain water.  Research conducted by Dr. Ann Grandjean and her colleagues has shown that caffeinated drinks – most coffee, tea and soft drinks – should count towards the daily fluid intake for the majority of people. The authors' conclusion that “advising people to disregard caffeinated beverages as part of the daily fluid intake is not substantiated by the results” of their study, was published in 2000, in the peer-reviewed journal, Journal of the American College of Nutrition.

Perceived Benefits: For Some

Valtin discusses several scientific reports that show the benefits of high water intake in reducing the risk of certain diseases, such as cancer of the urinary bladder, colorectal cancer, and fatal coronary heart disease.  He adds, however, that the results are controversial in some instances, that the exact amount of water needed to achieve the benefits is not known and is sometimes less than 8 x 8, and that perhaps the preventative measure should be limited to those persons who have a propensity for those particular conditions. 

Potential Drawbacks: Water Intoxication

Dr. Valtin points out that even plain water may be harmful.  It can cause 'water intoxication,' which can lead to mental confusion, seizures, and even death.  Water intoxication occurs when the kidneys' excretion of water (urine) cannot keep pace with the fluid intake. Such conditions are being reported with increasing frequency in endurance athletes, military recruits, persons partaking in recreational drugs that cause extreme thirst, and in patients.

Conclusions

The author states that he has found no scientific basis for the 8x8 recommendation. He writes that when and if such proof is indeed obtained, the recommendations almost certainly should not be universally applied. In the interim, he feels that the burden of proof that absolutely every person needs to follow the 8x8 recommendation should fall on those who insist on it.

Dr. Valtin concludes that -- with the exception of some diseases and special circumstances, such as strenuous physical activity, long airplane flights and exposure to hot climates, Americans are probably drinking enough water -- and possibly even more than enough.

-end-

The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.

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Editor’s Note: To set up an interview with a member of the research team, please contact Donna Krupa at 703.527.7357 (direct dial), 703.967.2751 (cell) or djkrupa1@aol.com.