International Journal of Biometeorology

, Volume 49, Issue 4, pp 232–237 | Cite as

Effects of humid heat exposure in later sleep segments on sleep stages and body temperature in humans

  • Kazue Okamoto-MizunoEmail author
  • Kazuyo Tsuzuki
  • Koh Mizuno
Original Article


This study sought to investigate the effects of humid heat exposure in later sleep segments on sleep stages and body temperature in humans. The subjects were eight healthy males, from whom informed consent had been obtained. The experiments were carried out under three different sets of conditions: a control climate [air temperature (Ta)=26°C, relative humidity (RH)=50%] (C); a humid heat climate (Ta=32°C, RH=80%) (H); and a humid heat exposure in later sleep segments (C for the first 3 h 45 min, followed by a 30-min transition to H, which was then maintained for the last 3 h 45 min) (C–H). Electroencephalogram, EOG, and mental electromyogram, rectal temperature (Tre), and skin temperature (Tsk) were continuously measured. The total amount of wakefulness was significantly increased in H compared to C–H or C. Compared to C, wakefulness in C–H and H was significantly increased during later sleep segments. Tre and mean Tsk were significantly higher in H than in C–H or C. In C–H, Tsk and Tre increased to levels equal to those observed in H after Ta and RH increase. Whole body sweat loss was significantly lower in C–H and C than in H. These results suggest that humid heat exposure in the later sleep segment reduces thermal load as compared to full-night humid heat exposure. In daily life, the use of air conditioning in the initial sleep hours can protect sleep and thermoregulation.

Key words

Humidity Ambient temperature Sleep stages Body temperature 



This study was performed with Special Coordination Funds of the Ministry of Education, Culture, Sports, Science and Technology, the Japanese Government


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Copyright information

© ISB 2004

Authors and Affiliations

  • Kazue Okamoto-Mizuno
    • 1
    Email author
  • Kazuyo Tsuzuki
    • 1
  • Koh Mizuno
    • 2
  1. 1.National Institute of Advanced Industrial Science and Technology (AIST)IbarakiJapan
  2. 2.National Institute of Mental HealthNational Centre of Neurology and PsychiatryIchikawaJapan

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