You increase your chances of developing basal-cell skin cancers and melanomas if you expose your skin to sunlight or sunlamps, even if you apply a sunscreen.
Sunlight is classified into shorter wavelengths called UV-B, longer wavelengths called UV-A, and the very long wavelengths that are used in black lights.
Scientists used to think that the shorter UV-B rays caused cancer, while the longer UV-A and black light rays were far less likely to do so.
DNA, the genetic material in cells, is known to absorb the short UV-B waves which disrupt the genetic messages and cause cancer. Many tanning parlors claim their bulbs emit only the longer UV-A waves and therefore do not cause cancer, but recent research points to a connection between UV-A rays and cancer.
Research reported in the July 15 edition of Proceedings of the National Academy of Sciences shows that DNA also absorbs UV-A and even the longer wavelengths. Most sunscreens block only UV-B, the rays that are most likely to cause skin cancer.
If you will be in the sun, by all means apply sunscreen, but be aware that it offers only partial protection.
The best protection from sun damage is a roof. The next best protection is a hat and clothes to cover your skin.
Q: Should I be taking progesterone with estrogen after menopause?
A: The guidelines for the use of estrogen by postmenopausal women are fairly well established. However, there is considerable disagreement over the use of the second female hormone called progesterone.
A woman's body stops making much estrogen and progesterone when she stops menstruating permanently at the average age of 52. Lack of estrogen can cause bone weakening called osteoporosis, hot flashes and vaginal dryness. It can also cause heart attacks in susceptible women. All of these conditions can be alleviated by taking estrogen.
However, estrogen stimulates the uterus and breasts to grow. The second hormone, progesterone, stops the stimulation. Women who are given estrogen without also being given progesterone have their uterus stimulated all the time. This can lead to uncontrolled growth -- which is cancer.
Most doctors agree that a woman who has a uterus and is given estrogen should also be given progesterone to prevent uterine cancer. For a woman who does not have a uterus, the benefits of progesterone are still being debated.
The data is not clear enough to show whether taking progesterone prevents breast cancer, and some doctors believe progesterone will keep the estrogen from preventing heart attacks.
A recent study in the European Journal of Obstetrics, Gynecology and Reproductive Biology (May 1993) showed that progesterone may actually enhance the heart attack-preventing benefits of estrogen. Postmenopausal women who take both estrogen and progesterone had the same elevation of the
protective HDL cholesterol as those who take just estrogen. Furthermore, estrogen and progesterone raised blood levels of the good HDL when they were given continuously 365 days a year.
Q: I thought chicken was a low-fat food. Why do you say it should not be eaten on a low-fat diet?
A: Reducing your intake of red meat and replacing it with chicken usually does not help you lower cholesterol, reduce your weight, or prevent heart attacks and certain types of cancers. Compared to red meat, chicken has almost as many calories, almost as much cholesterol and only slightly less fat. Neither has any plant fiber.
A low-fat diet based on fruits, vegetables, whole grains and beans lowers cholesterol and body weight by getting you to eat more fiber. Fiber contains no calories and makes you feel full. You will be able to stay on a low-fat diet permanently because you can reduce your calorie intake without feeling hungry.
When you take in more calories than your body needs, the extra calories are converted to fat, even if they start out as carbohydrates or proteins. Saturated fat raises cholesterol only if you take in more calories than your body needs. If you got almost all your calories from meat but reduced your intake of calories by one third, your cholesterol would go down.
When you substitute chicken for red meat, you usually take in as many calories as you did previously. Your cholesterol may not go down and you may not lose weight. Furthermore, a high-protein diet can cause osteoporosis by causing calcium to leach out of your bones.
Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.
United Features Syndicate