Melatonin is a naturally occurring hormone that is formed mainly in the pineal gland. The pineal gland is the size of a small capsule and sits in the lower middle part of the brain. Descartes called the pineal gland the seat of the soul, but we now think of it merely as the source of melatonin, which regulates sleep and is involved in immune processes.
Melatonin release from the pineal gland has a predictable twenty-four-hour cycle: an increase in the evening is associated with drowsiness and sleep, and a decrease in the morning leads to wakefulness. Melatonin production from the pineal gland declines steadily with age, and this produces disruption of internal clocks and rhythms, particularly the sleep-wake cycle. Melatonin is a good hypnotic, particularly for jet lag. I know a couple of physicians who work for the pharmaceutical industry, and they fly an average of once a week between Europe and the United States. They are quite happy with melatonin's effects in giving them a good six hours of sleep on the flight, and feel that it is a good antidote for jet lag. Melatonin doses of 0.5 to 3 mg are usually sufficient to induce sleep.
Melatonin is an antioxidant, a superb scavenger of free radicals. Melatonin boosts its own antioxidant effect by promoting the activity of glutathione peroxidase, an enzyme that is also an antioxidant. Relatively high doses—3 to 20 mg daily—are taken for its antioxidant, and possible promemory, effects. Even in this higher dose range, it has few side effects. At doses above 100 mg daily, melatonin can do a reverse flip and cause insomnia and depression.
There have been many tall claims about the use of melatonin for a wide range of maladies, based primarily on results from animal studies. Clinical studies have focused on its sedative action, not its effects on memory. Its antioxidant activity suggests potential promemory effects. The lack of well-controlled studies using melatonin to treat mild memory loss or dementia, let alone to prevent memory loss, makes it difficult for me to recommend melatonin as a promemory agent. Also, I wonder if the anecdotal reports of melatonin's positive effects on memory are related to its property of inducing restful sleep and thus indirectly boosting daytime cognitive performance, rather than a direct memory-enhancing effect.
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