Endocrine Abstracts (2009) 20 OC6.5

Cortical bone size is associated with serum sex hormone-binding globulin levels in healthy men at the age of peak bone mass

Griet Vanbillemont1, Bruno Lapauw1,2, Youri Taes1, Veerle Bogaert1, Stefan Goemaere2, Hans-Georg Zmierczak2, Dirk De Bacquer3 & Jean-Marc Kaufman1,2

1Department of Endocrinology, Ghent University Hospital, Ghent, Belgium; 2Unit for Osteoporosis and Metabolic Bone Diseases, Ghent, Belgium; 3Department of Public Health, Ghent, Belgium.

Background: In elderly men, fracture risk is independently associated with higher serum sex hormone-binding globulin (SHBG) levels1. Previously, we observed lower free estradiol (E2) and higher SHBG levels in a three-generational family study of men with idiopathic osteoporosis2.

Objective: To investigate associations between serum SHBG levels and cortical bone size at age of peak bone mass.

Design: Six hundred and seventy-seven healthy male siblings aged 25–45 years were recruited in a cross-sectional, population-based study. This study is part of SIBLOS a broader study designed to investigate determinants of sex steroid levels and peak bone mass in men.

Methods: Cortical bone parameters at the radius and tibia (66% site, 2/3 of bone length from distal) were assessed using peripheral quantitative computed tomography (XCT2000, Stratec GmbH). In a morning blood sample, testosterone (T), E2 and SHBG levels were measured using immunoassays. Cross-sectional relations were investigated using linear mixed-effects modeling analyses.

Results: After controlling for age, weight and height, SHBG levels were positively associated with total and cortical bone area and mineral content, and with peri- and endosteal circumference at both radius and tibia (β=0.09–0.17; P=<0.001–0.016). No associations with volumetric bone mineral density or cortical thickness were found. These findings remained significant after adjusting for T and/or E2 levels.

Conclusions: This study demonstrated that higher serum SHBG levels are associated with larger bone size and thus more favorable indices of bone strength in healthy men at the age of peak bone mass, which seems in contrast with observations in elderly men and men with idiopathic osteoporosis. The underlying mechanism is presently unknown, but the possibility of a differential role of SHBG depending on sex steroid status might be considered.

References: 1. Mellström et al. JBMR 2008 23 1552–1560.

2. Van Pottelbergh et al. JCEM 2004 89 4949–4953.

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