Exercise Cuts Breast Cancer Risk after Menopause: New Data Show 10% Reduction, but Previous Prospective Studies Have Yielded Mixed Results

Article excerpt

ATLANTA -- In postmenopausal women, an active lifestyle provided about a 10% reduction in the risk of developing breast cancer over a 17-year period in over 36,000 women, according to findings from a prospective cohort study presented at the annual meeting of the American Society of Clinical Oncology.

The protective effect of physical activity was most significant against the risk of developing the more aggressive estrogen receptor (ER)-positive, progesterone receptor (PR)-negative form of breast cancer, providing a 34% reduction in risk, said Dr. Aditya Bardia, who was pursuing a degree at the University of Iowa in Iowa City, at the time of the study.

Dr. Bardia and colleagues from the Iowa Women's Health Study mailed questionnaires that addressed leisure time physical activity and breast cancer risk factors to postmenopausal women who were living in Iowa in 1986; 41,837 women (43%) responded.

The participants' levels of physical activity were classified as low, medium, or high based on the frequency and intensity of their exercise.

The investigators determined cancer incidence between 1986 and 2003 using the Iowa Surveillance, Epidemiology, and End Results (SEER) Cancer Registry and mortality information from state and national resources. Periodic follow-up surveys confirmed continued residence in Iowa in greater than 99% of the women each year.

After exclusion of women with cancer, a full or partial mastectomy, and those with incomplete data, the cohort included 36,363 women. During the 17-year follow-up period, 2,548 women were diagnosed with breast cancer at an average age of 71 years.

Overall, 47% of the women reported low physical activity, 28% reported medium physical activity, and 25% reported high activity. In addition to having a lower body mass index (BMI), active women were more likely to have received education beyond high school and reached menopause at an older age.

A high level of physical activity was associated with a 13% reduction in the risk of developing ER-positive breast cancer and an 8% reduction in ER-negative breast cancer, compared with low physical activity. …