INS and Insulin resistance: However, a meta-analysis of 47 RCTs involving 44,161 adults without diabetes (median duration: 4 months, dose: 4000 IU/day) revealed that vitamin D supplementation significantly reduced fasting blood glucose, fasting insulin, and homeostasis-model-assessment-estimated insulin resistance (HOMA-IR) levels, though no differences were observed in insulin secretion or β-cell function indexes [66].