Obey Your Thirst

by Paulette Avery, R.N., M.S.N.

The title I chose for this month's column is the slogan for a popular soft drink, but it can also be the guideline most of us use to be sure we are getting adequate fluid intake. And contrary to popular belief, we probably don't need to drink at least eight glasses of water each day to maintain healthy fluid levels. So where did the advice to drink at least 64 ounces of water a day come from?

According to a recent Associated Press article by Lauren Neergaard, Dr. Heinz Valtin, professor emeritus at Dartmouth Medical School, has spent 40 years researching how the body uses water and how much we need. His article reviewing the eight-glass-a-day theory was recently published in the American Journal of Physiology. Valtin believes the advice to drink at least eight glasses of water a day came from faulty interpretation of a 1945 report from the Food and Nutrition Board. The report stated that for each calorie of food consumed, the body needs about a milliliter of water. That works out to eight cups of water for the typical 2000-calorie diet. What has been left out is the report's statement that most of that amount of fluid is contained in prepared foods. In other words, we don't need to drink all that extra water because we are getting most of what we need from the foods we eat.

Eating the five to nine servings a day of fruits and vegetables that many experts now recommend would provide lots of fluid, as these foods are 80 percent to 95 percent water. Melons are an especially good source of water. Interestingly, even meat and breads contain a fair amount of water.

Apparently, other advice regarding getting enough fluid has been inaccurate as well. For example, the belief that drinking coffee and other caffeinated drinks does not count as fluid intake because the caffeine acts as a diuretic and causes fluid loss. As it turns out, people who drink caffeinated beverages regularly adjust to the diuretic effect and, as a result, do get hydrated by drinking them.

Another myth: if you feel thirsty, you are already dehydrated. For most of us, this is not true. The exceptions are athletes doing strenuous workouts and the elderly, who tend to lose their awareness of thirst. For the rest of us, drinking when we feel thirsty is a good idea and should keep us adequately hydrated.

Once again, moderation is the key. Dehydration is a serious condition, so it is important to drink enough. Obey your thirst, and check that your urine is a pale yellow color. These two indicators will usually keep you on track. In the other direction, overdrinking can lead to water intoxication in some cases, a condition in which too much water in the system causes a depletion of adequate sodium levels from the blood to the point that the body does not function properly. Water intoxication is more common in those with certain medical conditions and can also occur in teens who use the party drug Ecstasy. For the average healthy person, drinking more water than necessary simply results in the need to urinate more often.

The Institute of Medicine's Food and Nutrition Board plans to decide within the next six months or so whether to provide an official recommendation regarding daily water intake. In the meantime, let your body and your common sense guide you.

Paulette Avery is a registered nurse and a freelance writer specializing in health issues.