Melatonin is a hormone secreted by the pineal gland at the base of the brain. It plays an important role in regulating sleep and in maintaining circadian rhythm, the body's natural time clock. The hypothalamus keeps track of the amount of sunlight that is taken in by the eye. The less sunlight, the more melatonin that is released by the pineal gland, thereby enhancing and regulating sleep. Melatonin can also be taken in an over-the-counter supplement mainly sold in health food stores and pharmacies.
Melatonin also exerts a powerful antioxidant activity. The discovery of melatonin as an antioxidant was made in 1993.