Melatonin - a chronobiotic and soporific hormone.

In this report we review evidence that melatonin, a hormone produced by the pineal gland during the hours of darkness, plays a major role in the synchronization of the sleep/wake cycle. The production of melatonin is regulated by a structure located in the hypothalamus called the suprachiasmatic nucleus (SCN). The activity of the SCN is strongly affected by changes in illumination and, as a consequence, melatonin levels are high during darkness and low in the light and it, therefore, reflects the cycle. Changes in sleep/wake patterns are among the hallmarks of biological aging. Complaints of difficulty in initiating and maintaining sleep, and daytime drowsiness, are more common in the elderly than in any other age group. In this report, we review evidence that impaired meltonin secretion is associated with sleep disorders in old age. Circulating melatonin levels have been found to be significantly lower in elderly insomniacs than in age-matched controls, and their onset and peak times delayed. In view of these findings, we investigated the effects of melatonin treatment on melatonin-deficient insomnia in the elderly. From the results of our study, it seems likely that melatonin replacement therapy may be beneficial in the initiation and maintenance of sleep in this population.