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 Food Charts)
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.
[accessed December 3, 2010]
As Drs. Aaron E. Carroll and Rachel C. Vreeman reported in an article on this topic:
There’s nothing wrong with liking water, but there is no scientific proof stating that you need to drink anywhere near eight glasses a day. One doctor who has made this his research focus, Dr. Heinz Valtin, searched through many electronic databases and also consulted with nutritionists and colleagues who specialize in water balance in the body. In all of his research, and in all of the research we conducted to double-check his work, no scientific evidence could be found to suggest that you need to drink eight glasses of water a day. In fact, scientific studies suggest that you already get enough liquid from what you’re drinking and eating on a daily basis. We are not all walking around in a state of dehydration.
Other medical experts have also disdained the notion that one need drink at least eight glasses of water per day to remain adequately hydrated:
Kidney specialists do agree on one thing, however: that the 8-by-8 rule is a gross overestimate of any required minimum. To replace daily losses of water, an average-sized adult with healthy kidneys sitting in a temperate climate needs no more than one liter of fluid, according to Jurgen Schnermann, a kidney physiologist at the National Institutes of Health.
One liter is the equivalent of about four 8-ounce glasses. According to most estimates, that’s roughly the amount of water most Americans get in solid food. In short, though doctors don’t recommend it, many of us could cover our bare-minimum daily water needs without drinking anything during the day.
The best general advice is to rely upon your normal senses. If you feel thirsty, drink; if you don’t feel thirsty, don’t drink unless you want to. The human body already does a good job of regulating water balance on its own, and you therefore need not force yourself to drink when you are not thirsty for fear of being dehydrated. The exhortation that we all need to satisfy an arbitrarily rigid rule about how much water we must drink every day was aptly skewered in a letter by a Los Angeles Times reader:
Although not trained in medicine or nutrition, I intuitively knew that the advice to drink eight glasses of water per day was nonsense. The advice fully meets three important criteria for being an American health urban legend: excess, public virtue, and the search for a cheap “magic bullet.”
- Stomach does not have eyeballs to distinguish water from food.
Stomach treats water as food and food stays in stomach for 2 to 5 hours.
Until stomach is empty, stomach has to work hard.
- Stomach’s working hard results in higher heart rate and blood pressure.
For stomach to do its job, heart needs to pump lots of blood by raising heart rate.
These are usual indications of higher temperature of organs and disease, illness and/or pain.
In other words, drinking water is supposed to worsen symptoms.
- Both organs of stomach and heart use muscle.
Liver needs to work harder to suffice the greater needs of stomach and heart.
Thus, liver cannot focus on self-healing body.
- Kidneys and bladder have limited capacity.
Although these are as amazing as other organs of ours, they still have limited capacities.
When they have more water than necessity, they cannot focus on self-healing either.
Stomach became to be in excessive condition due to water will be subduing bladder more powerfully and bladder will be even more deficient.
Kidney and bladder are in charge of bone, marrow, will power and vital indicators of longevity.
- Don’t drink water unless you are thirsty.
Although you think you are thirsty, it might have been caused by your habit of drinking.
- Drink water with less amount and less frequency.
- If you need to wake up to urinate, you are already drinking too much water.
You are not supposed to wake up to urinate even though you are 70s or 80s years old.
- However, if you don’t drink much (intentionally or naturally) and have disease, try to drink more water for a couple of months
because you might have been dehydrated.