Increase in Osteocalcin Following Testosterone Therapy in Men With Type 2 Diabetes and Subnormal Free Testosterone

CONTEXT: One-third of men with type 2 diabetes have subnormal free testosterone concentrations. We evaluated the following: (i) whether bone mineral density (BMD) and bone strength are affected by gonadal status in type 2 diabetes and (ii) the effect of testosterone replacement on markers of osteoblast and osteoclast activity. DESIGN: This is a secondary analysis of a previously completed, randomized, placebo-controlled trial. Ninety-four men with type 2 diabetes were recruited; 44 had subnormal free testosterone concentrations. Men with subnormal free testosterone concentrations were randomized to receive intramuscular injections of testosterone or placebo every 2 weeks for 22 weeks. Dual energy X-ray absorptiometry scans were performed at baseline and at 23 weeks. RESULTS: Men with subnormal free testosterone had similar BMD compared with men with normal free testosterone. However, bone strength indices were lower in men with subnormal free testosterone. BMD was related to free estradiol concentrations (r = 0.37, P = 0.004 at hip), whereas bone strength was related to free testosterone concentrations (r = 0.41, P < 0.001). Testosterone replacement increased osteocalcin concentrations [mean change (95% CI), 3.52 (0.45, 6.59), P = 0.008]. C-Terminal telopeptide (CTx) concentrations also increased at 15 weeks but reverted to baseline following that. There were no changes in other bone turnover markers or BMD. CONCLUSION: We conclude that testosterone replacement resulted in an increase in osteocalcin and a transient increase in CTx, indicating an increase in osteoblastic activity and transient increase in bone breakdown. Therefore, a major action of testosterone is to increase bone turnover in men with type 2 diabetes.