Monday, December 1, 2008
Why Eight Glasses of Water?
Wherever did the "Eight Glasses" of water requirement come from?
When working with patients to estimate their fluid needs, calculations are based on one's size and calorie intake. A person is estimated to need one cc (or one milliliter) of water for each calorie they consume. An average calorie intake is 2000 calories per day. This is the level on which the daily values are based on food labels. When translating the metric 2000 milliliters (ml) to ounces, you divide 2000 by 30 because there are 30 ml in one ounce. You get 66 ounces, divide by 8 ounces per cup, and that is just over eight cups of water! This is why you always hear people suggest you need about eight, 8-oz cups of water each day.
If you are a larger person and consume more calories or if you are more active, you will need to adjust upwards and drink a few more glasses to adjust for metabolizing the extra calories, or to compensate for losses in sweat. Likewise, if you are a smaller person and consume fewer calories you might be fine drinking just six glasses of fluid each day. Extra fluids you do drink in moderation are easily excreted by your kidneys, so unless your doctor has suggested otherwise, at least eight glasses is suitable for anyone in good health.