Sex Hormone-Binding Globulin as an Independent Determinant of Cortical Bone Status in Men at the Age of Peak Bone Mass

Abstract

Sex steroids are important determinants of the skeletal development, growth, and maintenance after achievement of peak bone mass. A large fraction of these hormones are bound by SHBG, and previous studies have shown that SHBG could be a determinant of bone characteristics. We investigated associations of serum SHBG levels with cortical and trabecular bone characteristics in young healthy men. A total of 677 healthy male siblings aged 25-45 yr were recruited in a cross-sectional, population-based study. Areal bone parameters were assessed using dual-energy x-ray absorptiometry. Cortical bone parameters at the tibia and radius and trabecular vBMD at the radius were assessed using peripheral quantitative computed tomography. Serum testosterone, estradiol, and SHBG levels were measured using immunoassays. Regression models including age, height, and weight showed that SHBG levels were positively associated with bone area at the hip and the whole body, but not with areal bone mineral density (BMD). Higher SHBG levels were associated with a larger cortical bone area and periosteal and endosteal circumferences at both the tibia and the radius, whereas trabecular volumetric BMD at the radius was negatively associated with SHBG levels. Associations persisted after adjustment for (free) sex steroid levels. No associations were found with cortical volumetric BMD or cortical thickness. In this population of healthy adult men at the age of peak bone mass, SHBG levels were positively associated with cortical bone size, independently from sex-steroid levels. This suggests a possible independent role of SHBG in the determination of adult bone size.