Sex steroid metabolism in the regulation of bone health in men

The growth and maintenance of both the female and the male skeleton are influenced by sex steroids. Although the regulation of the female skeleton by estrogens is well established, the relative importance of androgens and estrogens for the male skeleton remains uncertain. Evidence from cross-sectional and longitudinal studies suggests that serum estradiol levels are more strongly associated with bone mineral density, bone turnover and bone loss than testosterone levels are in adult men. In addition, it appears that a threshold level of serum estradiol exists for optimal skeletal maturation and prevention of both bone loss and fractures. Also, the specificity of the assay technique should be considered when examining serum sex steroid levels in epidemiological cohorts, with a preference for the gold standard mass spectrometry. Additionally, serum levels of sex steroid metabolites, rather than the bio-active sex steroids, may be better markers of local sex steroid action at the target tissue level. In this respect, serum levels of glucuronidated androgen metabolites appear to provide additional information as markers of local androgenic activity in bone than the bio-active androgens. Taken together, even though an important role of testosterone is not excluded, estradiol is an important regulator of bone health in men.