To further evaluate the potential influence of extent of vitamin D deficiency at baseline and intake interval on the observed effects, subgroup analyses were carried out and revealed that vitamin D supplementation was effective in ameliorating insulin resistance in women with PCOS who have baseline serum vitamin D < 20 ng/ml (fasting insulin, SMD: −0.40, 95% CI: −0.69, −0.10; Figure S1(a)) (HOMA-IR, SMD: −0.25, 95% CI: −0.47, −0.02; Figure S1(b)) (QUICKI, SMD: 0.52, 95% CI: 0.11, 0.92; Figure S1(c)). This evidence concerns the gene INS and vitamin D deficiency.