Vitamin D supplementation in infertile men: a systematic review and meta-analysis of effects on semen quality and endocrine function

Objective: To evaluate the effects of oral vitamin D supplementation on semen parameters, reproductive hormones and fertility outcomes in infertile men. Methods: We searched PubMed, Cochrane Library, Web of Science, Scopus and Embase for studies published within the last 10 years. Randomized controlled trials (RCTs) and observational studies evaluating oral vitamin D supplementation in infertile men and reporting semen parameters, reproductive hormones and/or fertility outcomes were included. Risk of bias was assessed using RoB 2.0 (RCTs) and ROBINS-I (observational studies). Results: = 1,168) were included. Vitamin D supplementation was associated with small but statistically significant improvements in semen volume, sperm concentration, progressive motility and serum testosterone. No significant effects were observed on clinical pregnancy or live birth. Reporting of adverse events was limited; no vitamin D-related serious adverse events were reported. Conclusions: Vitamin D supplementation may improve selected semen parameters and testosterone levels in infertile men, particularly progressive sperm motility. However, current evidence does not demonstrate improved clinical fertility outcomes, and higher doses (>4,000 IU/day) do not appear to confer additional benefits. Larger, well-designed trials with standardized fertility endpoints are needed to confirm clinical efficacy.