Vitamin D is increasingly recognized as a pleiotropic steroid hormone influencing numerous physiological systems, including reproductive function. Over the past decade, evidence has demonstrated a strong link between vitamin D deficiency and impaired ovarian function, suboptimal endometrial receptivity, reduced sperm quality, and adverse outcomes in assisted reproductive technologies (ART). This comprehensive review synthesizes clinical and mechanistic evidence on the role of vitamin D in female and male infertility, emphasizing ovulation, polycystic ovary syndrome (PCOS), endometrial function, ART outcomes, and male reproductive parameters. Systematic analysis of studies published from 2010 to 2025, including randomized controlled trials, cohort studies, and meta-analyses, shows that sufficient serum 25-hydroxyvitamin D 25(OH)D levels are associated with improved reproductive parameters, including higher ovulation rates, enhanced implantation, clinical pregnancy, live birth rates, and better sperm quality and motility. Supplementation studies suggest potential benefits in correcting vitamin D deficiency in women with PCOS, women undergoing ART, and men with impaired sperm parameters, although heterogeneity in dosing regimens, baseline populations, and outcome measures limits definitive clinical recommendations. Mechanistic evidence indicates that vitamin D regulates steroidogenesis, endometrial immunomodulation, insulin sensitivity, placental angiogenesis, and spermatogenesis, which may underlie its clinical effects. While current findings support routine assessment and correction of vitamin D deficiency, optimal serum targets, timing, and supplementation protocols require further investigation. Large-scale randomized trials are necessary to establish standardized clinical guidelines and confirm long-term reproductive benefits in both sexes.
Piotrowska et al. (2026) studied this question.