1270 Effects of Heat and Humidity on Sleep Parameters: Insights from 24.2 Million Nights Using an Under-Mattress Sleep Monitoring Device

Abstract Introduction Environmental conditions, particularly temperature and humidity, are increasingly recognized as modifiable factors influencing sleep. Amid global warming, rising temperatures and greater humidity variability make understanding these environmental effects even more essential. Leveraging under-mattress sensors, large-scale real-world datasets now allow precise quantification of night-to-night environmental perturbations and their impact on sleep parameters. Methods We analyzed the relationship between bedroom environment and sleep parameters using a large longitudinal dataset comprising approximately 24.2 million nights from 201,619 users (45.2% female, 53.8% male, 1.0% unspecified gender, with mean (SD) age of 49.7(13.0) years) collected across three summer-centered periods (2023–2025) recorded with validated commercial under-mattress sleep-monitoring devices (Fullpower Technologies). The impacts of within-participant indoor temperature and relative humidity (RH) changes on sleep stage composition and on AHI were modeled via mixed-effects models. Results Warmer-than-usual nights were associated with consistent shifts in sleep-stage composition. Each +1°C increase was linked to a decrease in REM proportion by 0.44% (99.9% CI −0.46 to −0.42) and Deep Sleep proportion by 0.12% (99.9% CI −0.15 to −0.08), with a concomitant increase in Light proportion by 0.16% (99.9% CI +0.16 to +0.17). Humidity anomalies showed similar but smaller effects. Each +1 percentage-point RH increase reduced REM proportion by 0.064% (99.9% CI −0.070 to −0.058) and Deep Sleep proportion by 0.081% (99.9% CI −0.091 to −0.072), while increasing Light Sleep proportion by 0.035% (99.9% CI +0.033 to +0.038). Additionally, AHI increased 0.88% (99.9% CI [0.82%,0.94%]) per +1°C increase and 0.29% (99.9% CI [0.27%,0.31%]) per +1 percentage-point RH. Conclusion In this population-scale real-world study, warmer and more humid nights shifted sleep toward lighter stages and increased respiratory burden. These findings highlight the physiologic sensitivity of sleep to small environmental changes and the importance of microenvironment monitoring in sleep research and clinical care. As global warming accelerates such fluctuations, these effects are likely to become increasingly relevant for population sleep health. Support (if any)