Melatonin is a hormone produced by the pineal gland of all mammals, including humans. The pineal is small, light-sensitive organ located in the brain that secretes melatonin only during darkness. Humans begin producing melatonin as early as 3 months old. The production of melatonin increases until age 20 at which point melatonin production begins to decrease. Melatonin affects a number of processes in humans such as sleep and temperature. Melatonin also appears to play a role in the promotion of growth and maturity. Low levels of melatonin in humans have been associated with depression, fibromyalgia, insomnia, some seizure disorders, and other conditions. Melatonin is used in connection with a variety of problems including sleep disturbances often associated with jet lag.