Serum estradiol is associated with lean mass in elderly Swedish men

Objective: Association studies in men have shown that androgens are inversely related to fat measures, while the relation between sex steroids and lean mass remains unclear. We, therefore, investigated the associations between serum sex steroid levels and body composition in elderly men with a main focus on lean mass measures. Design and methods: A cross-sectional survey of a population-based cohort of 3014 elderly men, aged 69-80 years (Osteoporotic Fractures in Men study, Sweden). Serum levels of testosterone and estradiol (E-2) were measured by mass spectrometry, sex hormone-binding globulin (SHBG) levels were measured by IRMA, and measures of body composition were obtained by dual-energy X-ray absorptiometry. Results: Total as well as free serum testosterone associated independently inversely (P<0.001), while total as well as free serum E-2 associated independently directly (P<0.001) with total body fat mass and trunk fat mass. Serum SHBG associated independently inversely with central fat distribution. Serum E-2 and free E-2 but not serum testosterone or free testosterone levels associated positively with lean mass (P<0.01). Elderly men within the lowest quartile of free E-2 had 0.5 kg less lean mass in the legs than subjects within the highest quartile, while the subjects in the different quartiles of free testosterone did not differ in lean mass. Conclusions: Serum E-2, but not serum testosterone, is directly associated with lean mass in this large study of elderly Swedish men. In addition, serum SHBG is associated with central fat distribution and we confirmed that serum testosterone is inversely associated with fat mass.