High night-to-night variability in ambient temperature is associated with increased sleep timing irregularity

OBJECTIVES: Daily temperature variability is projected to increase in some world regions up to 100% by 2100. This study investigated associations between night-to-night temperature variability with sleep duration timing and regularity. METHODS: Data were collected from global users of the Withings Sleep Analyzer (n = 125,295) and ScanWatch (n = 238,550) between January 2020-September 2023. Sleep regularity was assessed using intra-monthly variation in sleep duration and timing (onset, midpoint and offset). Ambient temperature data were extracted from established climate models to calculate night-to-night temperature variability. Fixed-effects models were used to assess the association between night-to-night temperature variability and sleep regularity (duration and timing). RESULTS: Participants (n = 313,822) were middle-aged (50 ± 15 years), 70% male, with an average 17 months of data. During months with high vs. low night-to-night temperature variability (99th percentile: 4.3°C vs. 50th percentile: 1.9°C), sleep onset variability was higher in southern (mean [95%CI]; 17.9 [16.1, 19.6]min), central (6.5°C vs. 1.0°C; 32.2 [29.8, 34.6]min) and northern locations (5.5°C vs. 2.1°C; 11.4 [11.2, 11.7]min). There was greater variability in sleep midpoint and offset with higher night-to-night temperature variability, with similar effect sizes. High night-to-night temperature variability was associated with