Girls, young women can cut risk of early breast cancer through regular exercise

St. Louis, May 13, 2008 — Mothers, here’s another reason to encourage your daughters to be physically active: Girls and young women who exercise regularly between the ages of 12 and 35 have a substantially lower risk of breast cancer before menopause compared to those who are less active, new research shows.

In the largest and most detailed analysis to date of the effects of exercise on premenopausal breast cancer, the study of nearly 65,000 women found that those who were physically active had a 23 percent lower risk of breast cancer before menopause. In particular, high levels of physical activity from ages 12 to 22 contributed most strongly to the lower breast cancer risk.

The study, by researchers at Washington University School of Medicine in St. Louis and Harvard University in Boston, will be available online May 13 in the Journal of the National Cancer Institute.

“We don’t have a lot of prevention strategies for premenopausal breast cancer, but our findings clearly show that physical activity during adolescence and young adulthood can pay off in the long run by reducing a woman’s risk of early breast cancer,” says lead investigator Graham Colditz, M.D., Dr.P.H., the Niess-Gain Professor and associate director of Prevention and Control at the Siteman Cancer Center at Washington University School of Medicine and Barnes-Jewish Hospital. “This is just one more reason to encourage young girls and women to exercise regularly.”

One-fourth of all breast cancers are diagnosed in women before menopause. Numerous studies have shown that physical activity reduces the risk of postmenopausal breast cancer, but the few studies that have looked at the influence of exercise on breast cancer risk before menopause have produced conflicting results.

For the current analysis, researchers examined data on a subset of women enrolled in the Nurses’ Health Study II, a prospective study of registered nurses ages 24 to 42. These 64,777 women had filled out detailed annual questionnaires about their levels of physical activity from age 12 on. After six years of follow-up, 550 women had been diagnosed with breast cancer.