title: Fatigue and sleep under large summer temperature differences.
abstract: BACKGROUND
  It has been recognized that an increase in outdoor ambient temperatures has a negative impact on health, particularly fatigue and sleep quality; however, the relationship among fatigue, sleep quality, and air temperature has yet to be sufficiently elucidated.
  
  
  OBJECTIVE
  To examine whether fatigue and sleep quality in a healthy Japanese population were affected by rising air temperature at three time points in summer and to investigate the confounding factors for fatigue.
  
  
  METHODS
  A total of 602 healthy volunteers in Osaka, Japan, participated in a survey that was conducted at the end of July, August, and September in 2010. The questionnaire consisted of four sections; demographic variables, accommodation status, fatigue, and sleep quality. We used the Chalder fatigue scale for assessment of fatigue, and the Japanese version of the Pittsburgh Sleep Quality Index (PSQI) for assessment of sleep quality.
  
  
  RESULTS
  The fatigue score was positively correlated with the sleep quality score in the total cohort. All the questionnaires at the three time points were completed by 162 participants. There were significant differences in fatigue scores among the surveys. We stratified the subjects into two groups of good and poor sleepers using a cutoff value of the PSQI. The good sleepers did not show differences in fatigue score regardless of the change in air temperature. However, the fatigue score of poor sleepers was greater at higher air temperatures. The use of air conditioners, accommodation type, and subject's age were confounding factors for fatigue.
  
  
  CONCLUSIONS
  High air temperatures in summer increased fatigue in healthy volunteers, especially those with poor sleep patterns, depending on the use of air conditioners, accommodation status, and subject's age.
authors: Osaka City University, Graduate School of Medicine, Osaka 540-0051, Japan. Electronic address: hfujii@med.osaka-cu.ac.jp.
authors: Hisako
authors: H
authors: Fujii
authors: Osaka City University, Graduate School of Medicine, Osaka 540-0051, Japan; RIKEN Center for Life Science Technologies, Kobe 650-0047, Japan; Kansai University of Walfare Sciences, Department of Health Science, 3-11-1 Asahigaoka, Kashihara-shi, Osaka 582-0026, Japan. Electronic address: sfukuda@fuksi-kagk-u.ac.jp.
authors: Sanae
authors: S
authors: Fukuda
authors: Yokohama National University, Graduate School of Environment and Information Science, Yokohama 240-8501, Japan. Electronic address: narumi@ynu.ac.jp.
authors: Daisuke
authors: D
authors: Narumi
authors: The University of Tokyo, Graduate School of Frontier Sciences, Kashiwa, Chiba 277-8563, Japan. Electronic address: ihara-t@k.u-tokyo.ac.jp.
authors: Tomohiko
authors: T
authors: Ihara
authors: Osaka City University, Graduate School of Medicine, Osaka 540-0051, Japan; RIKEN Center for Life Science Technologies, Kobe 650-0047, Japan. Electronic address: yywata@riken.jp.
authors: Yasuyoshi
authors: Y
authors: Watanabe
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000389:Air Conditioning; D005221:Fatigue / Q000453:epidemiology* / Q000209:etiology; D005260:Female; D006798:Housing; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012621:Seasons; D012737:Sex Factors; D012890:Sleep; D012893:Sleep Wake Disorders / Q000453:epidemiology* / Q000209:etiology; D013696:Temperature; D055815:Young Adult
keywords: Fatigue; Sleep; Temperature differences