Case–control and prospective cohort studies confirmed a higher risk of glucose tolerance, insulin sensitivity and T2DM in participants with decreased melatonin [19,23,109]; treatment with melatonin elevated the levels of adiponectin, leptin, and ghrelin; reduced insulin resistance; and improved glycemic traits and diabetic complications [5,110,111]. The gene discussed is INS; the disease is type 2 diabetes mellitus.