According to a study published in the Journal of the National Cancer Institute, women who engaged in leisure-time exercise between the ages of 12 and 35 have a lower risk of developing premenopausal cancer than do women who were less active.

Several studies have shown that regular exercise is associated with a lower risk of postmenopausal breast cancer, but few studies have looked at the impact of exercise on premenopausal disease.

In this cohort study, Graham Colditz, M.D., of Washington University School of Medicine in St. Louis and colleagues examined exercise and the likelihood of developing breast cancer in a group of 64,777 women participating in the Nurses’ Health Study II. The researchers asked participants to fill out questionnaires on their physical activity starting from age 12. With six years of follow-up, 550 participants have been diagnosed with breast cancer.

The age-adjusted incidence rates for breast cancer was 194 cases per 100,000 person-years in the least active women versus 136 cases in the most active. Women whose activity was equivalent to 3.25 hours per week of running or 13 hours per week of walking had a relative 23 percent reduced risk of disease compared with women who had been less active.

“These results suggest that consistent physical activity during a woman’s lifetime is associated with decreased breast cancer risk. Unlike many risk factors for breast cancer, physical activity is an exposure that can be modified,” the authors write.

SOURCE:
Journal of the National Cancer Institute, May 13, 2008