General Description
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.1,2
Synthetic melatonin is sold as a dietary supplement.
Health applications
- Insomnia
- Jet lag
- Antioxidant protection
Functions and uses
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.3,4
Jet lag
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 travellers
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.5-9
Insomnia
In recent years, melatonin has gained popularity as a sleep aid
for insomniacs. Clinical trials have produced mixed results, showing
melatonin to be effective in some types of insomnia but ineffective
in others. A number of studies indicate that melatonin supplements
can help improve sleep in cases of insomnia caused by disruptions
in the circadian rhythms, such as those found in the elderly,
blind people, and night-shift workers.10-17
Dosage/toxicity
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.18 Melatonin has shown remarkably
low toxicity in animal and human trials,19,20
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. |
