Effects of vitamin D supplementation on metabolic and endocrine parameters in PCOS: a randomized-controlled trial

Randomized controlled trial in premenopausal women with polycystic ovary syndrome and vitamin D insufficiency (25[OH]D <75 nmol/L). In the vitamin D arm, 119 participants were randomized and 81 completed 24 weeks; analyses used intention-to-treat principles with outcome-specific available data.

Women in the active arm received cholecalciferol 20,000 IU weekly, given as 50 oily drops per week (Oleovit D3-drops), for 24 weeks. The regimen was compared with placebo.

Vitamin D supplementation did not significantly improve the primary metabolic outcome overall, but it did lower plasma glucose at 60 minutes during the oral glucose tolerance test. The adjusted treatment effect for plasma glucose area under the curve at 24 weeks was -9.19 (-21.40 to 3.02; p = 0.139), while 60-minute glucose decreased by -10.2 mg/dL (95% CI -20.2 to -0.3; p = 0.045). Vitamin D status and related endocrine markers improved: 25(OH)D increased by 33.4 nmol/L (95% CI 24.5 to 42.2; p < 0.001), PTH decreased by -6.6 (p = 0.004), and 1,25(OH)2D increased by 27 (p = 0.006). In women with baseline 25(OH)D <50 nmol/L, glucose AUC also decreased significantly at 24 weeks (-19.20; p = 0.021), but the overall trial conclusion was that metabolic and endocrine benefits were otherwise limited.

The primary endpoint was not significant overall, and several findings were secondary or subgroup analyses. Outcome-specific sample sizes were smaller than the randomized arm size, with some measures available only in subsets of participants. The trial was single-center and restricted to premenopausal women with PCOS and vitamin D insufficiency, limiting generalizability.