Abstract
The present study investigated whether room temperature (Ta) cycles around dusk and dawn could influence the circadian rhythm of rectal temperature (Tcore), urinary 6-hydroxymelatonin sulfate during nocturnal sleep, and subjective assessments of sleep in humans. Six female and two male students served as participants. Two different Ta conditions, cyclic and constant, were established. Two kinds of room temperature were provided to subjects: cyclic Ta (gradual decrease from 27°C to 24°C between 1800 and 2200 h and gradual increase from 24°C to 27°C between 0300 and 0700 h) and constant Ta (27°C over 24 h). At cyclic Ta, the circadian nadir of Tcore rhythm was significantly advanced, while Tcore was significantly lower from 2300 to 0200 h and significantly higher from 0600 to 1000 h. The nocturnal concentration of 6-hydroxymelatonin sulfate in the urine during sleep was significantly higher during cyclic Ta. Waking sensation just after rising was significantly better with cyclic Ta. (Skin temperatures in the extremities−Ta) were significantly higher with cyclic Ta especially during the evening and night. Our results suggest that gradual change of room temperature in the evening and early morning is important in terms of sleep promotion and fresh awakening. It seems probable that mankind has been evolved to have deeper sleep under the influence of cyclic Ta around dusk and dawn.
