Postmenopausal breast cancer risk lower with exercise

Postmenopausal women who report high levels of physical activity are at reduced risk of developing breast cancer, especially estrogen receptor-positive/progesterone receptor-negative tumors (ER+/PR-), than women who are less active, according to data from the Iowa Women's Health Study published in the Dec. 11/25 issue of the Archives of Internal Medicine.

Aditya Bardia, MD, MPH, of the Mayo Clinic College of Medicine in Rochester, Minn., and colleagues tracked women's self-reported levels of physical activity and breast cancer incidence, including tumor status, in a cohort of 41,836 women over 18 years. Those who reported high levels of physical activity had a 14% lower risk of developing breast cancer, compared with their less-active counterparts, and a 9% lower risk of breast cancer after researchers controlled for body mass index (BMI). This suggests that not all of the association was due to the effect of exercise on body weight. The association was strongest among women with ER? tumors. Specifically, women with high physical activity levels had a 34% lower risk of developing this type of cancer after adjusting for BMI.

"If found to be causally related to breast cancer, physical activity would have a substantial public health effect on the prevention of this disease, along with its other positive health benefits," the authors conclude.