Effects of Vitamin D Supplementation on Bone Turnover and Bone Mineral Density in Healthy Men: A Post-Hoc Analysis of a Randomized Controlled Trial

Vitamin D is well known for its effects on calcium and mineral metabolism. However, vitamin D effects on bone turnover markers (BTMs), which are used together with bone mineral density (BMD) to evaluate bone health, are less clear. We therefore examined vitamin D effects on BTMs (beta-cross laps (CTX) and osteocalcin (OC)) and BMD in a post-hoc analysis of a randomized controlled trial (RCT). This is a post-hoc analysis of the Graz Vitamin D&TT-RCT, a single-center, double-blind, randomized placebo-controlled trial conducted between December 2012 and November 2017 at the endocrine outpatient clinic at the Medical University of Graz, Austria. A total of 200 healthy men with serum 25-hydroxyvitamin D (25(OH)D) levels <75 nmol/L participated in the trial. Subjects were randomized to receive 20,000 IU of vitamin D3/week (n = 100) or placebo (n = 100) for 12 weeks. Outcome measures were BTMs, BMD, and trabecular bone score (TBS). A total of 192 men (mean age and 25(OH)D: 43 (+/- 13) years and 54.9 (+/- 18.3) nmol/L, respectively) completed the study. We found no significant treatment effect on BTMs, BMD, or TBS (p > 0.05 for all). In middle-aged healthy men, vitamin D treatment for 12 weeks had no significant effect on BTMs or BMD.