Fatigue and sleep under large summer temperature differences

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. Objectives: 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.