A longitudinal large-scale objective sleep data analysis revealed a seasonal sleep variation in the Japanese population

ABSTRACT

In the contemporary era, when life habits are largely determined by social needs and individual preferences, sleep is nevertheless affected by seasonal environmental changes. Japan has large seasonal and geographical alterations of photoperiod and climate. Japan does not adopt the daylight saving time (DST) system, making it a suitable country for the study of seasonal variations in natural human sleep. The aim of this study was to analyze the seasonal changes in the sleep properties (timing and quality) and identify their relationship with environmental changes. Here, we report an analysis of objective sleep data of 691 161 nights collected from 1856 Japanese participants (age 20–79 years, male 91%, female 9%) for 3 years using contactless biomotion sensors. Sleep onset time did not show clear seasonal variation, but sleep offset time showed a seasonal change with a single latest peak in winter. Seasonal variation was larger during weekends than during weekdays. Sleep offset time well correlated with sunrise time but was different in spring and autumn even when the sunrise time was same, suggesting the role of temperature difference. Sleep quality, estimated by wake time after sleep onset and sleep efficiency, showed seasonal changes with the lowest trough around mid-summer. In conclusion, despite profound social influences, the timing and quality of sleep showed seasonal fluctuation indicating that they were influenced by climate factors even in the developed country.

Keywords:

• Sleep
• seasonality
• biomotion sensor
• outside temperature
• photoperiod

Acknowledgements

The authors would like to thank the users of the sensor for their participation to this study, Dr. Till Roenneberg (Ludwig Maximilians University) for constructive comments, and Dr. Masahiro Tohkin (Nagoya City University) for advice on the statistics.

Declaration of Interest

The instruments used in this study were developed and sold by Omron Healthcare Co., Ltd. This work was carried out as a collaboration between Omron Corporation, Omron Healthcare Co., Ltd., Kumamoto University, and Kuwamizu Hospital. All the cost of data collection and data analysis were defrayed by Omron Healthcare Co., Ltd.

Supplementary Material

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Additional information

Notes on contributors

Kazuhiko Kume

MH, HN, TS, MT, KK contributed to the sensor development, conceived the study design, MH and KK analyzed the data, wrote the manuscript, KK directed the study.