Key Takeaway
Higher outdoor or indoor temperatures are consistently associated with degraded sleep quality and quantity worldwide, with limited evidence of fast human adaptation to heat.
Summary
This systematic review examined the relationship between ambient temperature and sleep outcomes measured in real-world settings across the globe. The authors searched PubMed, Scopus, JSTOR, GreenFILE, GeoRef, and PsycARTICLES for studies published before February 2023, including research conducted among adults, adolescents, and children.
The findings showed that higher outdoor or indoor temperatures are generally associated with degraded sleep quality and quantity worldwide. The negative effects of heat persist across multiple sleep measures and are strongest during the hottest months and days, in vulnerable populations (elderly, low-income), and in the warmest regions. Critically, the review found limited evidence of fast sleep adaptation to heat, suggesting that rising temperatures from climate change and urbanization pose a serious threat to human sleep, health, performance, and wellbeing.
Only six of the included studies investigated temperature-related sleep responses in tropical regions, despite those areas being home to roughly 40% of the global population. Study quality was generally assessed as low to moderate, highlighting the need for higher-quality research using objective sleep measures in diverse climates.
Methods
- Systematic review of multiple databases (PubMed, Scopus, JSTOR, GreenFILE, GeoRef, PsycARTICLES)
- Included studies published before February 2023
- Focused on real-world ambient temperature and valid sleep outcomes
- Included studies of adults, adolescents, and children
- Quality assessed using a 14-item research quality checklist
- Narrative synthesis of findings
Key Results
- Higher temperatures consistently associated with worse sleep quality and quantity
- Negative effects strongest during hottest months and days
- Vulnerable populations (elderly, low-income) more affected
- Warmest regions showed strongest associations
- Limited evidence of rapid human adaptation to heat during sleep
- Both outdoor and indoor temperature elevations impair sleep
Limitations
- Study quality generally low to moderate
- Only 6 studies from tropical regions (40% of global population)
- Heterogeneity in sleep outcome measures across studies
- Narrative synthesis rather than quantitative meta-analysis
- Most studies from temperate climates in developed countries