AimUsing a meta-analysis framework, we investigated the association between the serum level of vitamin D and the risk of polycystic ovary syndrome (PCOS) and further examined the therapeutic effect of vitamin D on the clinical features of PCOS. Material and MethodsMultiple databases were searched to retrieve studies. We chose clinical studies that investigated the relation between the serum level of vitamin D and the risk of PCOS or the therapeutic effect of vitamin D on PCOS. The search results were screened according to strict inclusion and exclusion criteria to select high-quality studies for inclusion. Statistical analyses were carried out using stata 12.0. ResultsSeventeen studies were eligible in this meta-analysis. The levels of 25-hydroxyvitamin D and the quantitative insulin-sensitivity check index in the PCOS group were remarkably lower than in the controls, whereas the homeostasis model assessment of insulin resistance in the PCOS group was markedly higher than in the controls. No statistically significant difference was observed in serum parathyroid hormone levels between the two groups. The 25-hydroxyvitamin D levels were significantly elevated after PCOS patients received vitamin D-3 treatment, but serum parathyroid hormone concentration, homeostasis model assessment of insulin resistance and quantitative insulin-sensitivity check index did not show any significant changes, indicating a lack of therapeutic response. ConclusionOur results suggest that the serum level of vitamin D is associated with the risk of PCOS, but the therapeutic effect of vitamin D on PCOS remains to be further explored.