Brief report: melatonin facilitates sleep in individuals with mental retardation and insomnia.

Mentally retarded people typically exhibit poor sleep efficiency and reduced nocturnal plasma melatonin levels. The daytime administration of oral melatonin to those people, in doses that raise their plasma melatonin levels to the nocturnal range, can accelerate sleep onset. We examined the ability of similar, physiological doses to restore nighttime melatonin levels and sleep efficiency in mentally retarded subjects with sleep deficits. In a double-blind, placebo-controlled study, mentally retarded subjects (n = 20) received, in randomized order, a placebo and two melatonin doses (0.1, and 3.0 mg) orally 30 minutes before bedtime for a week. Treatments were separated by 1-week washout periods. Sleep data were obtained by polysomnography on the last three nights of each treatment period. The physiologic melatonin dose (0.3 mg) restored sleep efficiency (p < 0.0001), acting principally in the midthird of the night; it also elevated plasma melatonin levels (p < 0.0008) to normal. The lowest dose (0.1 mg) also improved sleep.