Health: Sweat Cure Exercise may prevent cancer

If lower blood pressure and a better mood are not incentive enough for starting to exercise regularly, consider this: scientists now believe that lifelong physical exertion also protects against cancer and diabetes. In Boston last week researchers at the annual meeting of the American Association for the Advancement of Science reported that athletic women cut their risk of breast and uterine cancer in half and of the most common form of diabetes by two-thirds. Says Harvard Reproductive Biologist Rose Frisch, who led the 5,398-woman study: "The long-term effects of early exercise on health are impressive."

Researchers believe the benefits occur because exercise shuts down the production of certain reproductive hormones in both men and women. The effect is more pronounced, however, in females. Vigorous training, for example, can temporarily lengthen or even eliminate a runner's menstrual cycle. The response appears to have a healthy effect. In a separate study of ten rowers at Harvard, Frisch found that active women produce a less potent form of estrogen than their sedentary counterparts. Result: breast and uterine tumors that depend on the hormone cannot develop as easily. In addition, athletes lack excess body fat, which can predispose people to diabetes.

Frisch cautions that low estrogen levels can lead to temporary infertility. Still, the benefits of exercise seem to outweigh the risks, particularly for teenagers. Frisch notes that very active girls started menstruating around 15, three years later than average. The advantages, she believes, are twofold: better health later in life and a lower risk of teenage pregnancy.