Impact of overheated bedroom conditions on sleep thermal comfort and sleep quality based on an experimental study

<p dir="ltr">This study investigates the effects of overheated bedroom conditions on measured sleep quality, subjective sleep experience, and sleep thermal comfort, specifically testing the new overheating threshold of 29°C proposed for UK bedrooms that places an upper limit on the mean night-time bedroom temperature. 22 participants (11 females, 11 males) in the age range of 25-50 years with no sleep disorders were monitored over two periods: a baseline period of 5 nights when the participants slept in their own bedrooms under typical summertime temperatures in English bedrooms, and a period of 3 nights in a thermally controlled overheated bedroom in which the temperature was maintained at 30°C ±0.5°C. Objective sleep metrics, such as Total Sleep Time (TST), Time in Bed (TIB), Sleep Efficiency (SE),Wake%, Sleep Onset Latency (SOL), and Fragmentation Index (FI) were measured using wrist actigraphy, alongside self-reported sleep quality, freshness, and sleep thermal comfort. Baseline sleep quality and sleep thermal comfort metrics were compared with those experienced under overheated condition. While TIB, SE, and SOL remained relatively stable, TST showed a significant reduction of 24 minutes under overheated conditions, indicating a meaningful decline in sleep duration. Participants reported significantly lower self-rated sleep quality (p<0.001) and freshness (p<0.001) in overheated conditions, highlighting the value of self-reported sleep quality monitoring. The analysis of thermal comfort votes confirmed significant discomfort in overheated conditions (p=0.002) with participants reporting a significant preference for cooler temperatures (p=0.008). Our results show that a bedroom temperature of higher than 29°C degrade both sleep quality and sleep thermal comfort, supporting the newly proposed upper threshold for temperature in UK bedrooms. Further research on mitigation strategies, such as cooling technologies and personalised interventions, is needed to reduce thermal stress and protect sleep health.</p>