What to watch with Vitamin D 25-OH and Fruchtbarkeit?

The link between vitamin D (25-OH) and fertility is plausible but not as robust as often marketed. Vitamin D receptors are expressed in reproductive tissues, and observational studies associate low 25-OH levels with longer menstrual cycles, poorer oocyte quality, and lower pregnancy rates. In men, correlations with sperm motility and morphology exist. However, randomized controlled trials (RCTs) show only modest benefits from supplementation, mainly in women with confirmed deficiency. A 25-OH level below 30 ng/ml (75 nmol/l) is considered suboptimal, but routine high-dose supplementation without deficiency is not advised. Caution: excess can cause hypercalcemia. Consumer tests typically measure total 25-OH, not the active form or binding proteins. Interpretation should consider sun exposure, lifestyle, and co-nutrients (magnesium, vitamin K2). Evidence: human-moderate.