It’s common knowledge that we should drink at least eight glasses of water a day. Or at least many people think it’s common knowledge.
Heinz Valtin, a Dartmouth Medical School physician, disagrees.
In an invited review published by the American Journal of Physiology, Valtin reported that there is no supporting evidence to back up the popular recommendation to drink eight 8 oz. glasses of water per day.
How did the 8 X 8 myth start? Valtin thinks that the notion may have started in 1945 when the Food and Nutrition Board of the National Research Council recommended approximately “1 milliliter of water for each calorie of food,” which would amount to roughly 2 to 2.5 quarts per day (64 to 80 ounces).
In its next sentence the board stated, “[M]ost of this quantity is contained in prepared foods.” But that last sentence seems to have been missed, so that the recommendation was erroneously interpreted as how much water a person should drink each day.
You may be surprised to find out many foods are high in water content. Below I have provided an abbreviated chart that lists the water content of some popular foods (Hale, 2007; Hale, 2010). The water percentage of each food is listed after its name.
Water Content of Foods
Bean sprouts: 92
Chicken, boiled: 71
Cucumbers, raw: 96
Eggplant, raw: 92
Lettuce, head: 96
Peaches, raw: 90
Peppers, green: 94
Potatoes, raw: 85
Strawberries, raw: 90
Turkey, roasted: 62
(The information above was referenced from Survival Acres)
Caffeinated beverages and other drinks also should be counted toward daily water intake. University of Nebraska researcher Ann Grandjean and colleagues (Grandjean, 2000) conducted a study, published in the Journal of the American College of Nutrition, about the effects of caffeinated beverages on hydration. Grandjean and her colleagues used 18 healthy male adults for their subjects.
On four separate occasions, the subjects consumed water or water plus varying combinations of beverages. The beverages were carbonated, caffeinated, caloric, and noncaloric colas and coffee. Body weight, urine, and blood evaluations were performed before and after each treatment.
Grandjean found that there were no changes in the body weight, urine, or blood evaluations for the different beverages. The study found no significant differences in the effect of various combinations of beverages on the hydration status of healthy adult males. Grandjean concluded that advising people to disregard caffeinated beverages as part of their daily fluid intake is not supported by the results of her study.
She went on to say, “[T]he purpose of the study was to find out if caffeine was dehydrating in healthy people who are drinking normal amounts. It is not.” There seems to be a large number of people who hold onto the myth that caffeine causes dehydration, probably because that’s what they have always heard.
Under some circumstances, significant fluid intake — at least eight 8-ounce glasses — is advisable: for the treatment or prevention of kidney stones, for example, as well as under special circumstances, such as performing strenuous physical activity or enduring hot weather.
However, most people currently are drinking enough water and, in some cases, more than enough. There is potential harm in drinking too much water (Hale, 2010). Water intoxication, a life-threatening condition, can occur when one drinks excessive amounts of water.
Water intoxication occurs when the kidneys are unable to excrete enough water (as urine), which leads to dilution of blood sodium. Mental confusion and death can result.
The bottom line? Drink when you are thirsty, not because you believe you need to.
GrandJean, AC., Reimers, KJ., Bannick, KE., Haven, MA. & Haven, MC. (2000). The effect of caffeinated, non-caffeinated, caloric and non-caloric beverages on hydration. Journal of the American College of Nutrition 19 (5):591-600.
Hale, J. (2007). Knowledge and Nonsense: The Science of Nutrition and Exercise. Winchester, KY: MaxCondition Publishing.
Hale, J. (2010). Should I Eat the Yolk? Separating Facts From Fiction To Get You Lean, Fit And Healthy. Berkeley, CA: Ulysses Press.
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Last reviewed: By John M. Grohol, Psy.D. on 8 Dec 2010
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Hale, J. (2010). The Myth Behind Drinking 8 Glasses of Water a Day. Psych Central. Retrieved on May 18, 2013, from http://psychcentral.com/blog/archives/2010/12/08/the-myth-behind-drinking-8-glasses-of-water-a-day/