What role does Vitamin D 25-OH play in fertility?

The role of vitamin D (25-OH) in fertility is an active area of research but remains inconclusive. Vitamin D receptors are expressed in reproductive tissues such as ovaries, endometrium, and testes, suggesting a biological role. Observational studies have linked low 25-OH vitamin D levels to female infertility, PCOS, endometriosis, and poorer IVF outcomes. In men, associations with reduced sperm quality have been reported. However, randomized controlled trials (RCTs) show mixed results: supplementation may improve fertility in deficient individuals, but no clear benefit is seen in those with sufficient levels. Thus, the evidence is moderate – plausible mechanisms and associations exist, but strong causal proof is lacking. Importantly, deficiency should be confirmed via blood test before supplementing, as excess vitamin D can be toxic. The provided context does not contain specific information on vitamin D and fertility; this answer is based on general medical knowledge. Caveat: single biomarker interpretation is limited; comprehensive fertility evaluation is recommended.