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

Cross-sectional study. To examine the association between serum testosterone levels (T levels) and bone mineral density after spinal cord injury (SCI). Medical research center. 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. 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. 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.