Body composition, sex steroids, IGF-1, and bone mineral status in aging men

Background. Bone loss in elderly men is associated with changes in body com position and reduced secretion of endogenous anabolizing hormones. The inde pendent influences of body composition and endocrine factors on male bone m etabolism, however, are unclear. Methods. Bone mass density (BMD) (bone mass content [BMC, g]/projected bone area [BA, cm(2)]) at different skeletal sites, skeletal muscle, and body f at mass were measured by dual-energy X-ray absorptiometry in 129 men aged 2 0 to 95 years. Free testosterone, 17-beta -estradiol, dehydroepiandrosteron e-sulfate, and insulin-like growth factor 1 (IGF-1) serum concentrations we re measured. Because BMD may fail to control for differences in skeletal si ze, the associations of bone mass with body composition and hormones were s tudied by comparing BMD regression models incorporating age and knee height only with BMC regression models also incorporating BA. Results. Skeletal muscle had close associations (p at least < .01) with BMD and BMC at almost all skeletal sites, but the strength of these associatio ns was generally reduced in BMC with respect to BMD models. Weak associatio ns (p < .05) were found in both models for fatness with femoral bone and fo r 17-beta -estradiol with total body and femoral bone. The association of 1 7-beta -estradiol with spinal bone was significant (p < .05) in the BMD but not in the BMC model. No association of BMC or BMD with androgens and IGF- 1 reached significancy. Conclusions. Skeletal muscle may be more important than fatness and anaboli zing hormones in preserving bone mass in elderly men. In contrast to tradit ional belief, estrogens may be more important than androgens and IGF-1 in m ale bone metabolism.