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My friends don't seem to drink as much water as I do. Is it possible to drink too much water?

"While drinking upward of eight glasses of water a day can be beneficial for some active people," says Edward Alexander, M.D., professor of medicine and physiology at BU's School of Medicine, "the facts are that no two people are alike. Each person has different hydration needs.

"The kidneys need a certain amount of water in order for the excretion process to function properly," he says. "But the amount depends on the person and his or her lifestyle. Obviously the quantity of water you should drink varies widely, based on how active you are. Athletic people need to drink so they don't become thirsty. If you become thirsty while exercising, you've gone too long without water.

"There's no truth to the theory that athletes should load up on water prior to a workout, because the body does not have the ability to store water and then distribute it as necessary. The average person excretes 80 percent of what he or she consumes within two hours.

"There are no known health benefits to drinking an excessive amount of water, and some potential health hazards do exist. Consuming too much water could lead to problems as severe as brain damage. If you drink more water than your body can excrete, brain cells can become swollen, affecting brain function. But," cautions Alexander, "we're talking about a tremendous amount of water -- upwards of 12 to 14 liters per day. Even lesser amounts could harm those with kidney or heart disease because their bodies may not be able to excrete fluids normally.

"More often than not," Alexander concludes, "it's not drinking enough water that puts a person's health at risk." Dehydration is a condition where the body tries to replace the water missing from the blood with water from other cells in the body, such as brain and muscle cells, causing them to shrink. As these cells shrink, it becomes more difficult for these areas, particularly the brain, to function properly.

Alexander offers simple advice to determine if you need to drink more water: look at the color of your urine. Dark urine indicates the need for more water; light urine indicates dilution and adequate hydration.

"Ask the Bridge" welcomes readers' questions. E-mail bridge@bu.edu or write to "Ask the Bridge," 10 Lenox Street, Brookline, MA 02446.

14 September 2001
Boston University
Office of University Relations