By Dr. Mercola
You've seen it on the old Food Pyramid. You might have heard it from your doctor. And you've certainly heard it countless times in conjunction with just about any diet ever created: if you want to be healthy you need to drink 8 glasses of water daily.
But what would you say if you knew the 8 glasses-a-day recommendation was a myth that actually evolved from a long-forgotten obituary of a doctor who advocated drinking lots of water?
And, what would you say if you I told you that the scientific evidence for needing 8 glasses of water a day just isn't there?
8 Glasses a Day Not Backed by Science
Water is, of course, essential for your survival. Every day, your body loses water through urine and sweat. This fluid needs to be replenished, for while you can survive for months without food, without water you wouldn't last more than a few days. If you get the fluid/water replacement issue right, then you have made one of the most important and powerful steps you can in taking control of your health.
But just how much water do you need to drink to replenish what you've lost? Writing in the American Journal of Physiology, Heinz Valtin of Dartmouth Medical School notes:i
"Despite the seemingly ubiquitous admonition to "drink at least eight 8-oz glasses of water a day" (with an accompanying reminder that beverages containing caffeine and alcohol do not count), rigorous proof for this counsel appears to be lacking.
This review sought to find the origin of this advice (called "8 X 8" for short) and to examine the scientific evidence, if any, that might support it. The search included not only electronic modes but also a cursory examination of the older literature that is not covered in electronic databases and, most importantly and fruitfully, extensive consultation with several nutritionists who specialize in the field of thirst and drinking fluids. No scientific studies were found in support of 8 X 8.
Rather, surveys of food and fluid intake on thousands of adults of both genders, analyses of which have been published in peer-reviewed journals, strongly suggest that such large amounts are not needed because the surveyed persons were presumably healthy and certainly not overtly ill."
As for the origins of this now widely accepted dietary dogma, the closest reference Valtin uncovered was a brief mention in the obituary of a well-known nutritionist by the name of Fredrick J. Stare, which said he was an "early champion of drinking at least six glasses of water a day."
Interestingly, Dr. Stare, who was a professor of nutrition and the head of the Department of Nutrition at Harvard School of Public Health, was a notable friend to industry, notorious for his outspoken support for food additives and water fluoridation. He also had ties to the tobacco industry and was a strong supporter of the sugar industry; he even reportedly earned the moniker "The Sugar King" at Harvard.ii
At one point, sometime during the late '50s, early '60s, Dr. Stare went so far as to publish an article stating that claims made by the Boston Nutrition Society that white bread was devoid of nutrients and a contributor to disease were "a cruel and reckless fraud."iii In other words, Dr. Stare believed white bread to be perfectly healthy, and openly criticized those who questioned food additives or excessive sugars in the diet, which isn't surprising considering his financial ties to Nabisco, Kellogg and the Cereal Institute.
The point is … Dr. Stare is also being credited with perhaps being among the first to promote drinking 6-8 glasses of water a day as healthy, which, given the source, deserves to be questioned.
Also mentioned by Valtin was a 1945 recommendation by the Food and Nutrition Board of the National Research Council, which recommended 2.5 liters of water as a "suitable allowance" of water for most adults. They, however, pointed out that "most of this quantity is contained in prepared foods," but it could be that people interpreted this to mean that 2.5 liters of water is the right amount to drink each day. The advice was repeated again in 1948, without a scientific backing.
Of course, consuming large quantities of water has been used as a medical therapy since the 19th century, when "hydropathists" advised patients to drink copious amounts of water to cure their ills. People have long been exploring the body's need for water, as well as what the optimal "dose" appears to be … but to date there's not much compelling evidence that the "8 8-ounce glasses a day" is the be all and end all in water consumption.
Are Bottled Water Companies Behind the Push to Drink More Water?
Last year, Dr. Margaret McCartney, a general practitioner from Scotland, wrote a commentary for the British Medical Journal arguing that the advice to drink 8 glasses of water a day is "thoroughly debunked nonsense" being spread by bottled water companies in order to churn up more profit.iv She pointed out that Hydration for Health, an initiative to promote drinking more water, is sponsored and created by French food giant Danone, which produces Volvic, Evian, and Badoit bottled waters. Interestingly, even claims that the elderly and children especially need to drink more water may also be unfounded.
A study in the American Journal of Clinical Nutritionv concluded that:
"… Healthy older adults maintain water input, output and balance comparable to those of younger adults and have no apparent change in hydration status."
McCartney also pointed out research done by Professor Stanley Goldfarb, physician and nephrologist at the University of Pennsylvania, and colleagues, which also found:vi
"There is no clear evidence of benefit from drinking increased amounts of water. Although we wish we could demolish all of the urban myths found on the internet regarding the benefits of supplemental water ingestion, we concede there is also no clear evidence of lack of benefit. In fact, there is simply a lack of evidence in general."
Interestingly, Goldfarb was contacted by Danone after the paper was published, McCartney notes:
"After he wrote his article, he was contacted by Danone, and taken out to dinner by two of its representatives. They didn't try to dissuade him from his views, but they did show him a graph intimating that sales fell after the editorial was published."
Drinking Too Much Water Can be Dangerous
There's a misconception with water consumption that the more you drink, the healthier you'll be. This is true to a point, particularly if you drink water in lieu of sugar-laden beverages like soda and fruit juice, but if you drink too much water, the sodium levels in your blood may drop to dangerously low levels, causing hyponatremia -- a condition in which your cells swell with too much water. While most of your body's cells can handle this swelling, your brain cells cannot, and most of the symptoms are caused by brain swelling. This condition is most common among athletes, although anyone can be affected by drinking excessive amounts of water.
Symptoms of hyponatremia include:
Confusion Decreased consciousness; possible coma Hallucinations Convulsions Fatigue Headache Irritability Loss of appetite Muscle spasms, cramps, or weakness Nausea Restlessness Vomiting
Most People DO Need to Drink More Water
Clearly, staying well hydrated is essential. But whether or not you actually need eight glasses of water or more each and every day is questionable, because hydration needs are so individual, and vary from day to day. You may very well need eight glasses of water a day.
Drinking eight 8-ounce glasses of pure water a day may not be likely to cause you harm; it's just that the evidence is lacking on whether that is the magic number for everyone, and most likely it appears that it is not.
The reality is that many people are dehydrated and would benefit from drinking more water each day, and from making water their primary source of fluids.
It does now appear that the notion that caffeinated drinks like coffee and tea cannot be counted as part of your fluid intake, as they act as a diuretic that will dehydrate you even further, may be another mythvii -- so if you drink these beverages you can "count" them as part of your fluid consumption. However, the bottom line is that you may not need to "count" your fluid intake at all. Instead, just let your body be your guide.
Your Body Will Let You Know When it's Time for a Drink
Your body will tell you when it's time to replenish your water supply, because once your body has lost between one to two percent of its total water, your thirst mechanism lets you know that it's time to drink some water!
Since your body is capable of telling you its needs, using thirst as a guide to how much water you need to drink is one way to help ensure your individual needs are met, day-by-day. Of course, if it's hot, exceptionally dry outside, or if you are engaged in exercise or other vigorous activity, you will require more water than normal. But again, if you drink as soon as you feel thirsty, you should be able to remain well hydrated even in these cases.
The color of your urine will also help you determine whether or not you might need to drink more. As long as you are not taking riboflavin (vitamin B2, also found in most multi-vitamins), which fluoresces and turns your urine bright yellow, then your urine should be a very light-colored yellow. If it is a deep, dark yellow then you are likely not drinking enough water. If your urine is scant or if you haven't urinated in many hours, that too is an indication that you're not drinking enough. (Based on the results from a few different studies, a healthy person urinates on average about seven or eight times a day.)
Pure clean water is the ideal beverage of choice for hydration, but remember you can get valuable fluids from fresh fruits, vegetables and certain foods, like homemade broth, too.