Fifteen years ago, members of the Washington Redskins didn't drink fluids while they practiced in the summer temperatures at Carlisle, Pa.
Six of their players, including their starting quarterback, passed out from heat strokes.
When you exercise in hot weather, you should always drink before you feel thirsty.
By the time you feel thirsty, you will have lost between two and four pounds of fluid; you will feel weak and tired; and you will be at increased risk for heat stroke.
Thirst is a very late sign of dehydration.
You lose a lot of fluid through your sweat when you exercise in the heat. Sweat has a lower salt content than blood, so you lose far more water than salt, and blood levels of salt rise.
When your blood level of salt rises very high, certain cells in your brain, called osmoreceptors, send off a signal to tell you that you are thirsty.
It takes a long time for blood salt levels to rise high enough to trip off the osmoreceptors.
The best way to prevent dehydration in hot weather is to drink a cup of fluid just before you start to exercise and try to continue drinking every 15 minutes while you exercise.
It doesn't matter what you drink; it can be water, soft drinks or fruit juice.
Sweet drinks taste better, so you are likely to drink more sweetened drinks.
The important point when you exercise in the heat is to make sure that you drink frequently, whether you're thirsty or not.
Q: I do aerobic dancing three times a week. Could this cause irregular periods?
A: Whether you are a recreational exerciser or a competitive athlete, if you have irregular periods or no periods at all you should check with your doctor.
You need to be evaluated and treated.
Women should menstruate every 25 to 35 days. When the interval between periods is more than 35 days or fewer than 25, a woman is almost always found to be deficient in one or both of the hormones estrogen and progesterone.
Estrogen stimulates the uterus to grow, and progesterone stops the stimulation. Women who lack progesterone have a uterus that is stimulated all the time. This can lead to uncontrolled growth, which is cancer.
Those who lack both estrogen and progesterone are at increased risk of suffering from osteoporosis.
Neither exercise nor excessive thinness cause irregular periods. At a recent conference, Dr. David Cummings of the University of Alberta in Canada presented data showing that so-called athletic amenorrhea is caused by not eating enough food.
The vast majority of women who develop irregular periods when they exercise will not have a serious cause and will have their periods return to normal when they eat more food.
If increasing your food intake does not give you normal periods, you need tests to rule out disease and probably will need to take estrogen and progesterone pills to protect you from uterine cancer and osteoporosis.
Q: My 77-year-old father has a high cholesterol count. Shouldn't he be on some kind of medication?
A: Having high blood cholesterol levels markedly increases your chances of having a heart attack when you are young, but not when you are older.
A recent report in the Archives of Internal Medicine (May 1993) recommends that doctors should be very cautious about using drugs to treat people over 70 who have high blood cholesterol levels. In this study, high cholesterol levels were present in people under 40 who suffered heart attacks, were far less likely to be associated with heart attacks in people from 41 to 70 years of age, and were irrelevant to a person's chances of developing a heart attack over age 70.
There are two components to a heart attack. First, high blood fat levels help fatty plaques to form in arteries. Then a clot forms to completely block the flow of blood to the heart.
High blood cholesterol markedly increase a person's chances of laying down plaques, but they do not predict increased susceptibility to forming clots.
This study shows that people who are over 70 and have no evidence of arteriosclerosis usually do not need to take drugs to lower their cholesterol.
Signs of arteriosclerosis include a history of heart pain, abnormal electrocardiograms or a heart attack. Even though there is no need to take drugs to treat his cholesterol, your father should be on a low-fat diet -- one based on fruits, vegetables, whole grains and beans -- to help reduce his chances of developing certain types of cancer.
Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.