Melatonin (N-acetyl-5-methoxytryptamine) is a hormone synthesized in the pineal gland from serotonin, a hormone derived from the amino acid tryptophan. A pea-sized gland located at the base of the brain, the pineal gland is part of the endocrine system and works in conjunction with other glands in the system, including the pituitary, thyroid, parathyroid, adrenals, ovaries, and testes. Melatonin secretion is stimulated by darkness and suppressed by light. The pineal gland's ability to produce melatonin declines with age, and some scientists believe this decline may play an important role in the aging process. Synthetic melatonin is sold as a dietary supplement.
Melatonin's main function is to help regulate the "biological clock," the circadian rhythms that control sleep/wake cycles and the production of other hormones throughout the body. The pineal gland is light-sensitive, increasing melatonin secretion after dark. The resulting increase in serum (blood) melatonin levels lowers body temperature and causes drowsiness. Serum melatonin levels generally peak around 2 a.m. and gradually decline to low concentrations by sunrise. In addition to its role in regulating circadian cycles, melatonin has been shown to have significant antioxidant activity.
Travel across multiple time zones can disrupt the body's normal circadian rhythms, interfering with sleep patterns, alertness, and energy levels in a phenomenon known as "jet lag." Melatonin supplements have become popular among long-distance travelers as a way to readjust the biological clock, and a number of placebo-controlled trials have shown melatonin to be effective in alleviating jet lag.
Most clinical trials have used doses of 2 to 10 mg of melatonin per day, and it appears to be safe at this dosage range. It is generally recommended that melatonin be taken 1 to 1/2 hour before bedtime. High doses (over 20 mg) may cause users to feel lethargic or disoriented. Melatonin has shown remarkably low toxicity in animal and human trials and no deaths from melatonin overdose have been reported. The effects of long-term melatonin use are unknown. The safety of melatonin supplementation during pregnancy has not been determined. Melatonin may cause drowsiness, and should not be taken before driving or operating heavy equipment. Because it may interact with some drugs, people taking prescription medications should consult their doctor or pharmacist before using melatonin.