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Melatonin, the hormone secreted by the pineal gland, tells us when to fall asleep, and helps us to remain asleep. Dr. Richard Wurtman discovered this in studies done over the past several decades.

Initially in studies on rats, Dr. Wurtman showed that

  1. melatonin is a true hormone;
  2. it is normally produced at nighttime; and
  3. that this daily rhythm in melatonin synthesis normally is generated by the environmental light cycle. Light, acting via the eyes, inhibits melatonin synthesis.

Subsequent studies by Dr. Wurtman showed that in humans, like rats, the hormone is produced at nighttime but not during the daytime. Moreover, in humans, nighttime melatonin production was found to decrease markedly with age, such that in most people over the age of 50, instead of having blood levels rising from 10 to 150 (picograms/ml) at 10 PM -midnight, they rise only to 20 or 30 (picograms/ml).

Dr. Wurtman suspected that the nighttime rise in blood melatonin levels might allow this rhythm to serve as a time signal to the brain, and that this signal might be used in turning on and maintaining sleep. In 1992 he showed that if young people received tiny doses (0.3 mg orally) of the hormone in daytime- when blood melatonin levels are very low -they became sleepy and fell asleep. (The sleep thus produced was normal, electroencephalographically.) The correct dose of melatonin for this purpose, 0.3 mg, was just sufficient to raise blood melatonin levels to their normal nocturnal range (150 picograms/ml), but very much lower than the dose sold for various unproved purposes in many health-food stores.

More recently, Dr. Wurtman's laboratory showed that the same doses of melatonin are also useful for the large number of old people who awaken during the night and have difficulty falling back asleep. In these people, the melatonin constitutes "replacement therapy", i.e., taken before bedtime, it restores nighttime blood melatonin levels to what they were when the user was younger. In a recently-published double-blind, placebo-controlled study, the "sleep efficiency" of previously-insomniac older people who took the 0.3 mg dose was undifferentiable from people without insomnia. In contrast, people who took the usual health-food-store dose (3 mg or more) had less of a beneficial response, and also developed unacceptable side-effects (like hypothermia).

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