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

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.

Effect of Ingestion of Ice Slurry on the Sleep Quality of Rugby Union Players in the Summer Season

“…Although ingestion of ice slurry 30 min before bedtime did not affect the wake time after sleep onset or sleep efficiency, ice slurry ingestion shortened the sleep latency and improved the subjective OSA-MA score for "feeling refreshed (recovery from fatigue)". Significant seasonal variations are known to exist in sleep quality parameters such as the sleep latency, sleep efficiency, and wake time after sleep onset, and the sleep quality is known to be often worse in the summer season than in other seasons [34]. One of the reported causes of poor sleep quality in the summer season is the change in body and skin temperature in hot environments [35][36][37].…”