Aerobic Exercise, Estrogens, and Breast Cancer Risk

Abstract

Abstract : With approximately 180,000 new cases reported in 2008, breast cancer continues to be the most frequently diagnosed non-skin cancer and second leading cause of cancer death among American women.1 A large body of epidemiological evidence suggests increasing levels of physical activity are associated with significant reductions in breast cancer risk.2, 3 The goal of this training grant was to investigate the effects of a 16-week, aerobic exercise intervention on endogenous sex hormone levels, menstrual cycle characteristics, and estrogen metabolism in sedentary, eumenorrheic, healthy premenopausal women. Main results from this exercise intervention include: 1) significant decreases in body fat and increases in lean body mass without body weight changes, 2) no significant changes in serum estradiol, estrone sulfate, testosterone, progesterone, and sex hormone binding globulin, 3) no significant changes in menstrual cycle length, and 4) limited changes in estrogen metabolism. The resulting increases in urinary 2-hydroxyestrone levels and 2-to-16-hydroxyestrone ratio are consistent with decreased breast cancer risk. These result support the hypothesis that hormonal changes, such as changes in estrogen metabolism, may be in part responsible for the favorable effects of exercise on breast cancer risk.