Seasonal Sleep Variations and Their Association With Meteorological Factors: A Japanese Population Study Using Large-Scale Body Acceleration Data.

Li Li,Yoshiharu Yamamoto,Junichiro Hayano,Toru Nakamura

doi:10.3389/fdgth.2021.677043

Abstract

Seasonal changes in meteorological factors [e.g., ambient temperature (Ta), humidity, and sunlight] could significantly influence a person's sleep, possibly resulting in the seasonality of sleep properties (timing and quality). However, population-based studies on sleep seasonality or its association with meteorological factors remain limited, especially those using objective sleep data. Japan has clear seasonality with distinctive changes in meteorological variables among seasons, thereby suitable for examining sleep seasonality and the effects of meteorological factors. This study aimed to investigate seasonal variations in sleep properties in a Japanese population (68,604 individuals) and further identify meteorological factors contributing to sleep seasonality. Here we used large-scale objective sleep data estimated from body accelerations by machine learning. Sleep parameters such as total sleep time, sleep latency, sleep efficiency, and wake time after sleep onset demonstrated significant seasonal variations, showing that sleep quality in summer was worse than that in other seasons. While bedtime did not show clear seasonality, get-up time varied seasonally, with a nadir during summer, and positively correlated with the sunrise time. Estimated by the abovementioned sleep parameters, Ta had a practically meaningful association with sleep quality, indicating that sleep quality worsened with the increase of Ta. This association would partly explain seasonal variations in sleep quality among seasons. In conclusion, Ta had a principal role for seasonality in sleep quality, and the sunrise time chiefly determined the get-up time.

Highlights

Several meteorological factors, such as ambient temperature (Ta), humidity, and sunlight, have significant influences on human biological rhythms, including endogenous circadian rhythms and sleep–wake cycles [1,2,3]
The present study aimed to examine the seasonal variations of sleep parameters in a Japanese population by using large-scale objective sleep data and to identity which meteorological factor significantly contributed to seasonal variations in each sleep parameter, if they exist, by multiple regression analysis combined with a bootstrapping method
The current study aimed [1] to examine seasonality in various sleep parameters (TST, in-bed time, get-up time, sleep latency (SL), sleep efficiency (SE), wake time after sleep onset (WASO), and wake episodes (WEP)) by using a large-scale objective sleep data of a Japanese population and [2] to identify meteorological factors statistically associated with sleep seasonality

Summary

Introduction

Several meteorological factors, such as ambient temperature (Ta), humidity, and sunlight, have significant influences on human biological rhythms, including endogenous circadian rhythms (e.g., rectal temperature and melatonin rhythms) and sleep–wake cycles [1,2,3]. The response of the systems to these seasonal inputs results in seasonal variations of biological variables, such as those of sleep properties. Seasonal variations in sleep quality or prevalence of insomnia has been well-studied in terms of associations with characteristic seasonal changes in sunlight durations, such as the midnight sun in summer and the dark period in midwinter, especially among Nordic populations. In the epidemiological survey on Norwegian sleep using questionnaires, insomnia was more frequent in winter than in other seasons of the year [6]. Other Nordic interview surveys demonstrated that the prevalence of reported insomnia, sleep onset problems, increased from summer to winter in northern Norway but decreased in the southern regions [7]. In a general population in Finland, the prevalence of sleep dissatisfaction increased during summer [8]

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