Nighttime temperature and sleep duration in the Chinese population

Ambient temperature influences sleep by modulating circadian thermoregulation. However, limited evidence exists regarding how extreme nighttime temperatures affect sleep in Chinese real-world settings. We collected 1,245,817 sleep records from 7,682 participants between 2017 and 2019 using wearable devices. Hourly temperature data were obtained from the land component of the fifth generation of European Re-Analysis. We adopted the hot night excess (HNE) and cold night excess (CNE) to quantify the intensity of nocturnal thermal stress. HNE and CNE were obtained by calculating the excess sum of nighttime high and low temperatures during hot and cold seasons, respectively. We employed mixed-effects models to assess the impact of extreme hot nighttime temperatures during the hot season and extreme cold nighttime temperatures during the cold season on sleep. We applied a distributed lag non-linear model to adjust for lagged effects of daytime temperature. Subgroup analyses were conducted to identify susceptible populations. During the hot season, a 5 °C increase in hot night excess was associated with a 0.81-minute reduction in total sleep duration (95% CI: -1.32, -0.31), primarily driven by a decrease in light sleep (-0.77, 95% CI: -1.22, -0.31). Conversely, during the cold season, a 5 °C decrease in cold night excess was linked to a 0.81-minute increase in total sleep (95% CI: 0.05, 1.17), with both light sleep (0.44, 95% CI: 0.12, 0.76) and deep sleep (0.35, 95% CI: 0.17, 0.53). These effects generally remained consistent after adjusting for the lagged effects of daytime temperatures. Elderly and obese individuals were more vulnerable to heat-related sleep disruptions. This study highlights the potential impact of climate change-induced nighttime warming on sleep and underscores the importance of optimizing thermal environments, particularly for the elderly and obese individuals, to enhance sleep duration during the hot season.