In this meta-analysis, 29 studies were analyzed (with a total of 22,250 participants) and they evaluated the effect of placebo-controlled folate supplementation, alone or in combination with other B vitamins, on fasting glucose, insulin, model evaluation of homeostasis for IR (HOMA-IR), HbA1c, or risk of T2DM. The gene discussed is INS; the disease is type 2 diabetes mellitus.