Virtually all scientists agree that you should drink during exercise to increase your endurance and prevent heat illness. However, until recently, they couldn't agree on how much sugar and salt your drinks should contain.
The factor that determines how quickly you can absorb fluids is how long the fluid remains in your stomach. Fluid is absorbed almost immediately after it leaves your stomach. Several previous studies showed that increasing the amount of salt in sports drinks increases the rate at which fluids leave the stomach, thereby helping them to be absorbed faster. However, a recent study from the Netherlands showed that salt helps to increase fluid absorption only when the sugar concentration of a drink is low. When the sugar concentration is high, it doesn't make much difference how much sodium and potassium salts are in the drink.
The best exercise drink is one that has between 3 and 9 percent sugar. It doesn't matter whether it is warm or cold, whether it is carbonated or not, or how much sodium and potassium it contains. Most drinks contain around 9 percent sugar because that's the concentration at which fluids taste best. The best sports drinks include all regular (not diet) carbonated soft drinks such as cola or ginger ale, fruit juices, tea with sugar, or anything else that is sweet enough to taste good. You can make your own drink containing 6 to 9 percent sugar by mixing 4 to 6 teaspoons of sugar and some lemon juice in a glass of water.
* Q: I want to help my 76-year-old father start an exercise program, but he's afraid of getting injured. What do you recommend?
A: Elderly people do get injured more easily, so your father is right to be concerned. You can help by teaching him how to exercise injury-free.
There's a set sequence of symptoms during exercise that xTC precede injuries. First your legs or arms feel heavy, then they burn and feel sore, next you feel pain in a single spot, and finally it hurts all the time, even when you sleep.
Young people can exercise through the heavy and burning feelings, but should stop when they feel pain in a single spot. They can then exercise at a very leisurely pace on the next day. However, when older people exercise through the burning feeling, they have to take the next day off or they are very likely to injure themselves.
Therefore, older people should set up a program in which they exercise up to the point when their muscles start to burn and then stop. But if they stop immediately when their muscles start to feel heavy and burn, they won't exercise very intensely or long and they won't become very fit. You can get around this by combining two or more sports in each exercise session. Pick two or more sports that stress different muscle groups; for example, pulling on a rowing machine and jogging. Start out by pulling on the rowing machine until the muscles in your arms or back start to feel sore, then stop. If you do not feel sore on the next day, you can repeat the workout.
Q: Does a vasectomy really increase the risk of prostate cancer?
A: Don't have your vasectomy reversed yet. A study of 26,000 men followed for 14 years showed that prostate cancer developed in 59 men who had vasectomies and in 39 who did not have that procedure. That's 1.51 times more frequent in the men who had vasectomies. But the study does not show that vasectomies cause prostate cancer.
During a vasectomy, a doctor cuts the vas deferens as it leaves the testicles. This prevents sperm from leaving the testicles but allows the fluid produced beyond the cut to be passed to the outside. So a man can have an apparently normal ejaculate that does not contain sperm.
You would not expect a vasectomy to cause prostate cancer, because it does not change a man's hormones. Prostate cancer is associated with the venereal wart virus and a high-fat diet. Men who have vasectomies may be more sexually active than those who do not have that procedure. Since they do not have to worry about impregnating a woman, they are far less likely to use condoms and are at increased risk of picking up venereal diseases, which increase the risk of prostate cancer. I believe the study demonstrates that the behavior associated with having a vasectomy may cause prostate cancer, not the vasectomy itself.
Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.