The sleep hormone, melatonin which is a key regulator of sleep could be also important link collecting circadian timing and insulin secretion. Melatonin production is suppressed by light and peaks around 3 to 5 hours after sleep onset. It regulates the sleep-wake cycle by lowering body temperature and causing drowsiness and promoting sleep. It was also shown that melatonin inhibits insulin secretion by pancreatic B cells. Sleep deprivation as well as age reduces melatonin production.