Effects of Vitamin D Supplementation on Semen Quality, Reproductive Hormones, and Live Birth Rate: A Randomized Clinical Trial

Randomized 1:1, placebo-controlled clinical trial conducted at a single center in Copenhagen, Denmark. The active arm included infertile men with impaired semen quality and vitamin D insufficiency (25OHD level <=50 nmol/L); 151 were randomized to vitamin D plus calcium and 133 completed.

Participants received an initial oral dose of 300,000 IU cholecalciferol, followed by cholecalciferol 1400 IU plus calcium 500 mg once daily for 150 days. The comparison arm received placebo; men were also instructed to avoid taking more than 400 IU/day of vitamin D outside the study.

Vitamin D plus calcium did not improve the main fertility outcomes in infertile vitamin D-insufficient men. At day 150, 25-OHD increased to 89 nmol/L versus 51 nmol/L with placebo, and inhibin B was higher (169 vs 154 pg/mL), but total sperm count, sperm concentration, motility, morphology, and overall live-birth outcomes were not improved. A subgroup signal suggested higher live-birth rates in men with oligozoospermia (35.6% vs 18.3%), but this finding was exploratory and not definitive.

Single-center trial with a modest sample size and a 150-day follow-up limits power to detect clinical fertility effects. The subgroup live-birth signal was not conclusive and requires replication, and the broader findings may not generalize beyond infertile men with vitamin D insufficiency in this setting.