BACKGROUND: The sleep-wake cycle and the rest-activity rhythm are known to change with aging, and such changes have been implicated in higher levels of depression as well as an increased incidence of dementia. However, information supporting seasonal changes in the sleep-wake cycle, the rest-activity rhythm and quality of life in older community-dwelling people remains insufficient. The aim of the present study was to prospectively investigate seasonal effects on the sleep-wake cycle, the rest-activity rhythm and quality of life among older people living in areas of Japan or Thailand with different climate classifications.
METHOD: The survey was conducted from March 2016 to May 2017, and 109 participants were recruited from Japan and Thailand: 47 older people living in Akita prefecture, Japan, and 62 older people living in Chiang Mai or Nakhon Ratchasima, Thailand. According to the Köppen-Geiger classification of Asian climates comprising tropical, desert, steppe, temperate and subarctic climates, Akita prefecture, which is located in northern Japan, is classified as a humid subarctic climate, while the Thai study areas are classified as tropical savanna. To monitor parameters of the sleep-wake cycle during nighttime (e.g. total sleep time, sleep latency, sleep efficiency, awaking time and frequency of sleep interruptions) and to calculate parameters of the rest-activity rhythm over the 24 h profile (e.g., interdaily stability, intradaily variability, relative amplitude, mean of least active 5 h period and mean of most active 10 h period), all the participants from both countries wore an Actiwatch 2 device on their nondominant wrist continuously for 7 days during each local season. The World Health Organization Quality of Life Questionnaire-BREF (WHOQOL-BREF) was also assessed during each local season.
RESULTS: The final sample size was 37 older people living in Akita prefecture, Japan, and 44 older people living in Thailand; these subjects completed the data collections during each local season. The dropout rates were 21% in Japan and 29% in Thailand. The results for the Japanese subjects showed a significantly shorter sleep time with higher levels of activity during the nighttime on summer (p < 0.001) and a fragmented rest-activity rhythm over the 24 h profile on winter (p < 0.001). The older Thai participants exhibited a poor state of night sleeping year-round, and a significant relationship was observed between seasonal variations in motor activity and the social domain of WHOQOL-BREF for each Thai season (|r| = 0.4, p < 0.01).
CONCLUSION: These findings provide new and important information regarding seasonal effects on the sleep-wake cycle, the rest-activity rhythm and quality of life in older community-dwelling people living in two different Asian climates. Consequently, clinical preventions targeting such seasonal variations might be useful for improving the quality of life of older Japanese and Thai individuals.
