Two recent RCTs reported a reduced risk of progressing from prediabetes to T2DM with supplementation; the first, in Iran, involved 162 participants aged 18–80 years with mean 25(OH)D concentration of ~12.5 ng/mL, fasting insulin of ~15 μU/mL, and a homeostatic model assessment of insulin resistance score raised at ~3–4 [34] and either impaired fasting glucose (IFG), impaired glucose tolerance (IGT), or both. This evidence concerns the gene INS and type 2 diabetes mellitus.