Exercise may help prevent cancer

By now, most women are familiar with the benefits of regular exercise in preventing heart disease, strengthening bones, lessening back pain and warding off other chronic diseases. What isn't well-known is something researchers have suspected for years: that exercise plays a strong role in preventing certain types of cancer, including breast cancer.

Recent research from the University of Southern California School of Medicine indicates that women who exercise regularly during childbearing years can significantly reduce their risk of developing malignant breast tumors. More than 1,000 women age 40 and under participated in the study. About half were recently diagnosed with breast cancer, while the other half, dTC similar in age and other characteristics, did not have the disease.


Q: What were some specific study findings?

A: Researchers found that, in contrast to inactive women, those who exercised four hours a week or more -- playing tennis, swimming or jogging, for example -- reduced their risk of breast cancer by almost 60 percent. Women who exercised less -- from one to three hours per week -- reduced their risk by about 30 percent.


Another major finding was that women who exercised for 10 years after puberty, but then stopped, lowered their breast-cancer risk by 50 percent. The critical implication for this discovery is that exercise during adolescence is crucial.

Q: What is the nature of the link between exercise and breast cancer?

A: The link between the two is not clear, according to the study. It speculates that regular physical activity may provide protection by altering the production of female hormones during menstrual cycles. More research should help to better define the connection.

It has generally been understood that the more menstrual cycles women have that include ovulation -- the point where the ovaries produce additional female hormones -- the greater their risk of breast cancer. A woman's cumulative exposure to these hormones is thought to be associated with breast-cancer risk. This may help explain why early pregnancy and early menopause have protective effects.

While these latest findings may constitute a major development in breast-cancer prevention, researchers stress that many other reasons exist to start and continue a regular exercise regimen. Additionally, they hope the study will encourage more physical-education programs nationwide, an area already acutely in need of attention.

According to a 1990 survey of high-school students, the majority of young women don't participate in physical education classes or exercise regularly.

Dr. Matanoski is a physician and epidemiologist at the Johns Hopkins School of Hygiene and Public Health. She is founding director of its Institute for Women's Health Research and Policy.