The male reproductive tract has been identified as a target tissue for vitamin D, and previous data suggest an association of 25-hydroxyvitamin D [25(OH)D] with testosterone levels in men.

We therefore aimed to evaluate whether vitamin D supplementation influences testosterone levels in men. Healthy overweight men undergoing a weight reduction program who participated in a randomized controlled trial were analyzed for testosterone levels. The entire study included 200 non-diabetic subjects, of whom 165 participants (54 men) completed the trial. Participants received either 83 μg (3 332 IU) vitamin D daily for 1 year (n=31) or placebo (n=23). Initial 25(OH)D concentrations were in the deficiency range (<50 nmol/l) and testosterone values were at the lower end of the reference range (9.09-55.28 nmol/l for males aged 20-49 years) in both groups.

Mean circulating 25(OH)D concentrations increased significantly by 53.5 nmol/l in the vitamin D group, but remained almost constant in the placebo group. Compared to baseline values, a significant increase in total testosterone levels (from 10.7±3.9 nmol/l to 13.4±4.7 nmol/l; p<0.001), bioactive testosterone (from 5.21±1.87 nmol/l to 6.25±2.01 nmol/l; p=0.001), and free testosterone levels (from 0.222±0.080 nmol/l to 0.267±0.087 nmol/l; p=0.001) were observed in the vitamin D supplemented group. By contrast, there was no significant change in any testosterone measure in the placebo group.

Our results suggest that vitamin D supplementation might increase testosterone levels. Further randomized controlled trials are warranted to confirm this hypothesis.