Alberta Physical Activity and Breast Cancer Prevention Trial: Sex Hormone Changes in a Year-Long Exercise Intervention Among Postmenopausal Women

Abstract

Purpose We examined how an aerobic exercise intervention influenced circulating estradiol, estrone, sex hormone–binding globulin (SHBG), androstenedione, and testosterone levels, which may be involved in the association between physical activity and breast cancer risk. Methods A two-center, two-arm randomized controlled trial of exercise was conducted in 320 postmenopausal, sedentary women age 50 to 74 years. Participants were randomly assigned to a 1-year aerobic exercise intervention of 225 min/wk (n = 160) or to a control group who maintained their usual level of activity (n = 160). Baseline, 6-month, and 12-month assessments of estrone, estradiol, androstenedione, and testosterone were quantified by radioimmunoassay after extraction, and SHBG was quantified by an immunometric assay. Intent-to-treat analyses were performed using linear mixed models. Results Blood data were available on 309 women (96.6%) at 12 months. Women in the intervention group exercised an average of 3.6 d/wk for 178 min/wk. At 12 months, statistically significant reductions in estradiol (treatment effect ratio [TER] = 0.93; 95% CI, 0.88 to 0.98) and free estradiol (TER = 0.91; 95% CI, 0.87 to 0.96) and increases in SHBG (TER = 1.04; 95% CI, 1.02 to 1.07) were observed in the exercise group compared with the control group. No significant differences in estrone, androstenedione, and testosterone levels were observed between exercisers and controls at 12 months. Conclusion This trial found that previously sedentary postmenopausal women can adhere to a moderate- to vigorous-intensity exercise program that results in changes in estradiol and SHBG concentrations that are consistent with a lower risk for postmenopausal breast cancer.