Melatonin is an endogenous monoamine hormone secreted by the pineal gland. Melatonergic signaling has been shown to play a role in circadian rhythm regulation, lipid and glucose metabolism, and obesity, and it has anti-inflammatory and antioxidant properties. The melatonin receptor 1B gene (MTNR1B) is expressed in, among other tissues, the brain and pancreatic beta cells, and risk variants for T2D have been reported as impairing early insulin secretion and increasing fasting glucose levels.1 Variants in the MTNR1B gene also have been reported in patients with depression (MDD).2