Higher Nocturnal Temperatures Shorten and Worsen Sleep with No Clear Evidence of Short-Term Compensatory Patterns

Background & Objectives Rising nighttime temperatures menace sleep, yet evidence from large longitudinal studies combining objective and subjective sleep measures remains limited. Here, we therefore examined associations of nocturnal air and wet-bulb temperature with seven sleep parameters, including possible delayed effects. Methods We analysed wearable-derived and subjective sleep data from 326 home-care workers (270 women) in Switzerland between June and Early October 2025, resulting in 14,290 participant-nights. Nocturnal air temperature and humidity data were obtained from the dense MeteoSwiss monitoring network (mean distance from participants' homes, 8.6 km). Bayesian multilevel models estimated nonlinear same-night within-person and between-person associations, while exploratory lag models examined whether associations with nocturnal temperature were also evident for exposures one and two nights earlier. Results Sleep maintenance efficiency, the primary outcome, showed no meaningful association with nocturnal air temperature. In contrast, warmer-than-usual nights were associated with shorter total sleep time and poorer subjective sleep quality. Compared with a participant's usual exposure, total sleep time was 13.3 min shorter at +5C, while subjective sleep-quality scores worsened by 1.2 points. At +5C, the probability of sleeping less than 7 h was 10.6 percentage points higher than at -4C relative to a participant's usual exposure. Changes in sleep-stage percentages and recovery index were very small. Wet-bulb results were broadly comparable while exploratory lag analyses provided little evidence of consistent delayed effects. Conclusions Higher nocturnal ambient temperatures were associated with shorter and poorer sleep, with no evidence of short-term compensatory patterns. The results thus underline that sleep disturbances may represent an important pathway linking warming nights to human health.