Relation of BMI and physical activity to sex hormones in postmenopausal women

Objective: Levels of estrogen, androgen, and prolactin have been related to risk of postmenopausal breast cancer. However, the determinants of these hormone concentrations are not established. The purpose of this study was to examine correlates of endogenous sex hormones. Research Methods and Procedures: Associations among adiposity, physical activity, and diet and concentrations of estradiol, free estradiol, estrone, testosterone, free testosterone, sex hormone-binding globulin (SHBG), androstenedione, dehydroepiandrosterone, dehydroepiandrosterone sulfate, and prolactin were evaluated in 267 postmenopausal women randomly selected from the Women's Health Initiative Dietary Modification Trial. Results: In multiple regression analyses on log-transformed hormones, BMI was positively associated with estrone (beta = 0.031, p < 0.001), estradiol (beta = 0.048, p < 0.001), free estradiol (P = 0.062, p < 0.001), free testosterone (P = 0.017, p = 0.02), and prolactin (beta = 0.012, p = 0.02) and negatively associated with SHBG (beta = -0.02, p = 0.001). Total physical activity (metabolic equivalent tasks per week) was negatively associated with concentrations of estrone, estradiol, and androstenedione (beta = -0.006, -0.007, and -0.005, respectively, all p <= 0.05). Using a composite variable of BMI and physical activity dichotomized by median values, women with high BMI/low physical activity had a mean estrone concentration of 28.8 pg/mL, compared with 24.1, 19.9, and 18.4 pg/mL for women with high BMI/high physical activity, low BMI/low physical activity, and low BMI/high physical activity, respectively (p trend < 0.001). Similar trends were observed for estradiol and free estradiol and, in inverse, for SHBG. Discussion: These associations may, in part, explain the positive associations between overweight/obesity and a sedentary lifestyle on breast cancer risk.