Mediators and moderators of the effects of a year-long exercise intervention on endogenous sex hormones in postmenopausal women.

OBJECTIVE: To identify factors that mediate or moderate the effects of exercise on postmenopausal sex hormone concentrations. METHODS: Postmenopausal women were randomized to 12 months of aerobic exercise for 200 min/week (n = 160) or to a control group (n = 160). Intention-to-treat analyses were performed using general linear models with sex hormone concentrations at 6 and 12 months as the outcome. Mediation by adiposity and insulin was investigated by examining changes in effect estimates after adjustment for changes in these factors over 12 months. Moderation was studied as the interaction between group assignment and eight baseline characteristics. RESULTS: Intervention effects on sex hormone-binding globulin (SHBG) and estradiol changes were attenuated with adjustment for change in overall body fat, while there was less attenuation adjusting for intra-abdominal fat change. Intervention effects on SHBG levels were unaffected by adjustment for insulin change. Significant interactions were identified between treatment and physical fitness (for SHBG and testosterone) and age (for testosterone), implying subgroup differences in intervention effect. CONCLUSIONS: Our data suggest that overall fat loss partially mediated exercise-induced changes in estradiol and SHBG concentrations. No previous RCT in postmenopausal women has studied moderators of exercise-induced sex hormone changes; therefore, future studies are needed to corroborate our results.