Postmenopausal sex hormones in relation to body fat distribution

Being overweight or obese increases the risk of postmenopausal breast cancer. A potential reason may be the frequently observed positive association of BMI with endogenous sex hormones and its negative association with sex hormone-binding globulin (SHBG). The purpose of this study was to investigate whether a woman's body fat distribution shows a BMI-independent association with these breast cancer-related biomarkers. Performing cross-sectional analyses among 1,180 postmenopausal women, we assessed whether associations of surrogates for an abdominal (waist circumference; waist-to-hip ratio, WHR) and gluteofemoral (hip circumference) fat distribution with estrone, total and free estradiol, androstenedione, total and free testosterone, and SHBG changed after adjustment for, or stratification by, BMI. All anthropometric measures were positively associated with estrogens and free testosterone, and negatively with SHBG. After adjustment for BMI, associations of free estradiol, free testosterone, and SHBG with both waist circumference and WHR remained significant, but all initially significant associations with hip circumference were abolished. In stratified analyses, waist circumference and WHR correlated with free estradiol, free testosterone, and SHBG in women with a BMI < 30 kg/m(2) but not in women with a BMI ≥ 30 kg/m(2). The latter suggests that in obese women, a possibly unique effect of abdominal fat on these biomarkers may be masked by the already large amount of overall body fat. On the whole, our results indicate that waist circumference and WHR, but not hip circumference, are associated with SHBG and SHBG-related sex hormones (free estradiol and free testosterone) independently of BMI.