Bodyweight influences the relationship between serum testosterone and bone mineral density in men with spinal cord injury.

Study Design: Cross-sectional study.

Objective: To examine the association between serum testosterone levels (T levels) and bone mineral density after spinal cord injury (SCI).

Setting: Medical research center.

Methods: Body composition assessments were measured in 53 men with chronic SCI. Serum T levels were measured after an overnight fast. Total and regional bone mineral density (BMD) and bone mineral content (BMC) were measured using dual-energy X-ray absorptiometry. Participants were classified into three groups based on their body weight [<65 kg, 65-80 kg, >80 kg] or serum T levels into low (400 ng/dl), mid-normal (401-544 ng/dl) and normal (>545 ng/dl) ranges.

Results: Serum T level was negatively related to body weight (r = -0.33, P = 0.016), fat mass (r = -0.46, P < 0.001) and percentage fat mass (r = -0.48, P < 0.001). There were no significant relationships between serum T levels and any of the bone health measurements. Body weight was related to total, regional (P < 0.01 for both) and knee BMD (P < 0.05). T level was only related to total and regional BMD in the group with body weight of 65-80 kg.

Conclusion: Testosterone has no direct relationship with BMD except within a specific weight group. However, body weight or fat mass negatively influences circulating T levels in men with SCI. The relationship between serum T levels and BMD is mediated by body weight in men with SCI.