Determinants of bone microarchitecture and mechanical properties in obese men

Abstract

Context: Recent studies have suggested that obesity in men is associated with increased fracture risk. Obesity in men is also associated with dysregulation of the GH/IGF-I and gonadal steroid axes, important regulators of bone homeostasis.

Objective: The aim of the study was to investigate body composition and endocrine determinants of bone microarchitecture and mechanical properties in obese men.

Design and setting: We conducted a cross-sectional study at a clinical research center.

Participants: Thirty-five obese men (mean age, 33.8 ± 6.4 yr; mean body mass index, 36.5 ± 5.8 kg/m(2)) participated in the study.

Outcome measures: Distal radius microarchitecture and mechanical properties were measured by three-dimensional high-resolution peripheral quantitative computed tomography and microfinite element analysis; body composition by computed tomography; bone marrow fat by proton magnetic resonance spectroscopy; total and free estradiol and testosterone; IGF-I; peak glucagon-stimulated GH; 25-hydroxyvitamin D.

Results: Men with high visceral adipose tissue (VAT) had impaired mechanical properties compared to men with low VAT (P < 0.05), despite comparable body mass index. VAT was inversely associated and thigh muscle was positively associated with mechanical properties (P < 0.05). Bone marrow fat was inversely associated with cortical parameters (P ≤ 0.02). Free estradiol was positively associated with total density (P = 0.05). Free testosterone was positively associated with trabecular thickness and inversely with trabecular number (P ≤ 0.05). Peak stimulated GH was positively associated with trabecular thickness, as was IGF-I with cortical area (P ≤ 0.04).

Conclusion: VAT and bone marrow fat are negative predictors and muscle mass is a positive predictor of microarchitecture and mechanical properties in obese men. Testosterone, estradiol, and GH are positive determinants of trabecular microarchitecture, and IGF-I is a positive determinant of cortical microarchitecture. This supports the notion that VAT is detrimental to bone and that decreased GH and testosterone, characteristic of male obesity, may exert deleterious effects on microarchitecture, whereas higher estradiol may be protective.

Fig. 1.

HR-pQCT of the distal radius in two representative obese men with comparable BMI but with high (A) and low (B) visceral fat (A, BMI, 32 kg/m², and visceral fat, 181 cm²; B, BMI, 32 kg/m², and visceral fat, 48.3 cm²). The subject with high visceral fat (A) has lower average, trabecular, and cortical bone density and trabecular and cortical thickness and cortical area than the subject with low visceral fat (B): average bone density, 251 vs. 450 mg HA/cm³; trabecular bone density, 183 vs. 218 mg HA/cm³; cortical density, 728 vs. 916 mg HA/cm³; trabecular thickness, 0.064 vs. 0.1 mm; cortical thickness, 0.4 vs. 1.18 mm; and cortical area, 42.5 vs. 83.5 mm².

Fig. 2.

Regression analysis of VAT and mechanical properties. There is an inverse association between VAT and failure load.