Purpose: Physical activity has been associated with a decreased risk for breast cancer. Mechanisms for this association may involve hormonal pathways. The Physical Activity for Total Health study is testing the effect of a 1-yr moderate intensity physical activity intervention on the endogenous sex hormone profile of postmenopausal women in a randomized controlled study.
Methods: Women (N = 168) who are aged 55-75 yr, not using sex hormones, sedentary, nonsmokers, have no endocrine-related disease or cancer, and with body mass index of 25.0 or greater, are eligible. Women are recruited through mass mailings and media advertising and are randomized to either a 1-yr moderate intensity aerobic and strength training exercise program (monitored group exercise sessions plus home exercise) or a control program (stretching classes).
Results: Serum hormones to be assayed at baseline and at the end of the study include: total estrone, total estradiol, free estradiol, percent bioavailable estradiol, estrone sulfate, sex hormone binding globulin, albumin, testosterone, free testosterone, androstenedione, dehydroepiandrosterone, dehydroepiandrosterone sulfate, insulin, glucose, and triglycerides. Other outcome measures include: the ratio of urinary 2-hydroxyestrone: 16alpha-hydroxyestrone (an estrogen metabolite ratio that may be associated with risk for breast cancer), weight, body mass index, total fat mass, and body fat distribution (waist:hip circumference ratio, DEXA scan, and abdominal fat measured by computed tomography).
Conclusion: This study is the first to examine the effect of change in physical activity level on sex hormones in postmenopausal women. It will provide insight into possible mechanisms through which physical activity might be associated with reduced risk of breast cancer.