What is melatonin?
Melatonin is a hormone made by the pineal gland, a small gland in the brain. Melatonin helps control your sleep and wake cycles. Very small amounts of it are found in foods such as meats, grains, fruits, and vegetables. You can also buy it as a supplement.
Melatonin and Sleep
A key factor in how human sleep is regulated is exposure to light or to darkness. Exposure to light stimulates a nerve pathway from the retina in the eye to an area in the brain called the hypothalamus. When the sun goes down and darkness occurs, the pineal is "turned on" by the SCN and begins to actively produce melatonin, which is released into the blood.
Natural melatonin secretion starts from the amino acid tryptophan, with serotonin as an intermediary, and then is released to the melatonin receptors in the brain, eye and other areas to help control the sleep and wake cycles. The melatonin half-life is short, roughly 20 to 50 minutes. It is metabolized (broken down) by the CYP-450 enzyme system in the liver and then excreted in the urine or feces.