Effects of vitamin D supplementation on androgens in men with low testosterone levels: a randomized controlled trial

PurposeIt has been hypothesized that vitamin D is associated with androgen levels in men. We, therefore, aimed to evaluate whether vitamin D supplementation increases serum total testosterone (TT) levels in men with low TT levels at baseline.MethodsThe Graz Vitamin D&TT-RCT is a single-center, double-blind, randomized placebo-controlled trial conducted between March 2013 and November 2017 at the endocrine outpatient clinic at the Medical University of Graz, Austria. One-hundred healthy men with serum TT levels <10.4 nmol/l and 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=50) or placebo (n=50) for 12 weeks. Primary outcome was TT measured using mass spectrometry. Secondary outcomes were free testosterone, free androgen index, sex hormone-binding globulin, estradiol, follicle-stimulating hormone, luteinizing hormone, metabolic characteristics, and body composition.ResultsNinety-four men [mean age and 25(OH)D: 47 (12) years and 56.3 (+/- 18.3) nmol/l, respectively] completed the study. We found no significant treatment effect on serum TT or on the remaining secondary outcome variables.Conclusion Vitamin D treatment had no effect on serum TT levels in middle-aged healthy men with low TT levels.