Sleep and Plasma Melatonin Rhythm in Subjects under Isolation with Dim Light: Effects of Physical Exercise

Abstract

Three male subjects spent 2 or 4 weeks together in an isolated facility with dim light condition (150 lx). In total, 11 subjects participated in this experiment. The daily life in the isolated facility was strictly scheduled. The subjects were divided into two groups; one group performed physical exercise for ca. 1 hour after lunch and the other group spent quietly. Sleep electroencephalography (EEG) and plasma melatonin rhythm were measured every second weeks. As a result, the plasma melatonin rhythms in the subjects without exercise showed significant phase-delay shifts 2 weeks after the start of isolation. In these subjects, the nocturnal sleep was deteriorated more than a little. For instance, the sleep latency was lengthened, the frequency of midnight wake was increased and the score of sleep satisfaction was decreased. By contrast, the peak phases of plasma melatonin rhythm were essentially unchanged with physical exercise. In these subjects, sleep was kept almost intact. These findings firstly indicate that a light-dark cycle with dim light (150 lx) is unable to keep the human melatonin rhythm entrained, and secondly confirmed that physical exercise accelerated entrainment of the human circadian pacemaker. Deterioration of sleep EEG seems to be a result of internal dissociation between the circadian pacemaker and the scheduled sleep time. [Jpn J Physiol 54 Suppl:S207 (2004)]