Vitamin D improved blood sugar and lipids in women with PCOS

Polycystic ovary syndrome is one of the most common endocrine conditions in women, and it reaches well beyond the ovaries: it affects both metabolic and reproductive health, often bringing raised blood glucose, insulin and unfavourable lipids. Vitamin D's possible role in metabolic regulation has attracted growing interest, raising the question of whether supplementing it could improve the metabolic side of PCOS. Individual trials have been small and scattered, so pooling them offers the clearest available answer. This review gathered the randomised evidence on vitamin D and glucose, insulin and lipid outcomes in women with the condition.

The reviewers searched PubMed, Embase, the Cochrane Library, Web of Science and ClinicalTrials.gov for randomised controlled trials of vitamin D supplementation in women with PCOS. Thirteen trials with 691 participants qualified. Results were pooled, study quality was assessed with the Cochrane Risk of Bias Tool, the certainty of the evidence was formally graded, and a trial sequential analysis checked whether enough participants had been studied for the main conclusions to be considered stable.

Vitamin D supplementation reduced fasting blood glucose by 2.91 mg/dL, insulin by 1.98 µIU/mL, triglycerides by 11.01 mg/dL, total cholesterol by 11.69 mg/dL, VLDL cholesterol by 2.64 mg/dL and LDL cholesterol by 5.85 mg/dL. HDL cholesterol was the one exception, showing no significant change. Checks for publication bias suggested a minimal probability of distortion, and the sequential analysis indicated the optimal sample size for major outcomes had been reached, supporting the robustness of the results.

This pooled result firms up a question that individual small trials could not settle, and the authors' additional checks lend the main findings more weight than a typical analysis of this size. The improvements sit squarely on the metabolic side of PCOS; the review does not address reproductive or hormonal outcomes. The most effective dose and the durability of the benefits over the long term were beyond what the included trials could show, and the authors explicitly flag both for future research.

For women with PCOS, this is a reason to see vitamin D as more than a bone nutrient: across pooled trials it improved fasting glucose, insulin and most of the lipid panel. What it cannot tell you is how much to take or for how long, since the optimal dose remains an open question the authors leave to future work. Vitamin D status is something a routine blood test can establish, which makes this a straightforward topic to raise with a clinician rather than a leap of faith.