Physical Activity and Breast Cancer: Is There a Link?

Extract

Physical activity has diverse physiologic effects through which it could potentially alter breast cancer risk. Currently, the most prominent hypothesis is that physical activity may lower risk through hormonal mechanisms. Estrogens are mitogenic to breast epithelial cells and are believed to play a key role in breast cancer promotion and possibly initiation ( 1 ). Older age at menarche, younger age at menopause, and perhaps a higher frequency of long and irregular menstrual cycles lower breast cancer risk ( 2 ). Compared with their more sedentary peers, highly trained athletes and dancers ( 3 ), and possibly recreational athletes ( 4 , 5 ), have delayed menarche and an increased frequency of long or irregular menstrual cycles. Although obesity is inversely related to the risk of premenopausal breast cancer, after menopause occurs, estrogens are synthesized from androgens in adipose tissue and obesity is directly related to risk ( 6 ). Physically active women of all ages are leaner than their more sedentary counterparts ( 7 ), but leanness is a major determinant of serum estrogen concentrations only for postmenopausal women ( 8 ). Because of its biological plausibility and consistency, the hypothesis that physical activity lowers breast cancer risk through hormonal mechanisms is intuitively appealing.