EFFECT OF INDUCING NOCTURNAL SERUM MELATONIN CONCENTRATIONS IN DAYTIME ON SLEEP, MOOD, BODY-TEMPERATURE, AND PERFORMANCE

We examined effects of very low doses of melatonin (0.1-10 mg, orally) or placebo, administered at 1145 h, on sleep latency and duration, mo od, performance, oral temperature, and changes in serum melatonin leve ls in 20 healthy male volunteers. A repeated-measure double-blind Lati n square design was used. Subjects completed a battery of tests design ed to assess mood and performance between 0930 and 1730 h. The sedativ e-like effects of melatonin were assessed by a simple sleep test: at 1 330 h subjects were asked to hold a positive pressure switch in each h and and to relax with eyes closed while reclining in a quiet darkened room. Latency and duration of switch release, indicators of sleep, wer e measured. Areas under the time-melatonin concentration curve varied in proportion to the different melatonin doses ingested, and the 0.1- and 0.3-mg doses generated peak serum melatonin levels that were withi n the normal range of nocturnal melatonin levels in untreated people. All melatonin doses tested significantly increased sleep duration, as well as self-reported sleepiness and fatigue, relative to placebo. Mor eover, all of the doses significantly decreased sleep-onset latency, o ral temperature, and the number of correct responses on the Wilkinson auditory vigilance task. These data indicate that orally administered melatonin can be a highly potent hypnotic agent; they also suggest tha t the physiological increase in serum melatonin levels, which occurs a round 2100 h daily, may constitute a signal initiating normal sleep on set.