Higher nighttime temperatures are strongly linked to shorter sleep durations and poorer sleep quality in US adults, says a new USC study. Researchers warn that people may lose up to 24 hours of sleep each year by 2099 if temperatures continue rising.
These findings underscore how climate change could directly affect sleep health, particularly among vulnerable communities and regions facing frequent heat exposure.
How Heat Disrupts Sleep
Warm nighttime conditions prevent the body from cooling down naturally, which is essential for falling asleep comfortably. Rising temperatures can also trigger stress responses that disrupt deep sleep and REM sleep.
These sleep interruptions can increase risks for cardiovascular disease, respiratory issues, and mental health problems. The study’s authors warn that climate-driven sleep loss may worsen public health outcomes over time.
Why This Study Is Different
Most earlier studies linking temperature to sleep lacked detailed health and demographic information. This limited understanding of who is most affected and why. The new research fills that gap by analysing rich data from the All of Us Research Program, a large US cohort that includes demographic, socioeconomic, and wearable-device information.
The findings were published in Environment International and conducted in collaboration with Harvard Medical School and Brigham and Women’s Hospital.
What the Data Revealed
Researchers examined sleep data from 14,232 adults collected between 2010 and 2022. Participants shared detailed demographic information along with Fitbit sleep data, allowing scientists to track sleep duration, sleep stages, and nighttime interruptions.
In total, the study analysed over 12 million nights of sleep and more than 8 million nights of sleep-stage data.
Key Findings
- A 10°C increase in daytime temperature led to an average 2.19 minutes of lost sleep.
- A 10°C nighttime increase caused 2.63 minutes of lost sleep.
- The impact was greater from June to September, when nighttime heat peaks.
- People on the West Coast lost nearly three times more sleep than those in other regions.
- Females, Hispanic individuals, people with chronic diseases, and those with lower socioeconomic status were most affected.
Although the loss may seem small per night, researchers emphasise its enormous cumulative impact across the population.
More Sleep Loss Expected as Climate Warms
Based on future temperature trends, the study estimates that US adults could lose 8.5 to 24 hours of sleep annually by 2099. Rising temperatures were also linked to more nighttime awakenings and longer periods spent awake in bed.
Which Groups Are Most at Risk?
Some populations face higher risks due to social, medical, or environmental factors. Lower-income households may lack access to cooling, while people with chronic illnesses often experience more heat sensitivity.
Communities in hotter regions, especially along the West Coast, face increased risk due to persistent nighttime heat events, says said Jiawen Liao, PhD, a postdoctoral research associate in population and public health sciences at the Keck School of Medicine of USC and first author of the study.
What Can Help Improve Sleep?
Researchers say targeted interventions and climate-adaptive policies could reduce heat-related sleep problems. Examples include:
- Expanding access to air conditioning in vulnerable neighbourhoods
- Increasing green roofs and urban green spaces to cool cities
- Updating building codes to require better insulation and ventilation
- Promoting indoor cooling programs for at-risk populations
Future research will also examine whether improving sleep through cooling strategies or sleep hygiene programs can reduce heat-related illness and mortality.
Q&A: What Readers Should Know
Q: Why do warmer nights affect sleep more than warmer days?
Nighttime heat interferes with the body’s ability to cool naturally, making it harder to fall asleep and stay asleep.
Q: Who is most vulnerable to heat-related sleep loss?
People with chronic health conditions, lower socioeconomic status, females, and Hispanic individuals are disproportionately affected.
Q: Why is the West Coast more affected?
Persistent heat waves, urban heat islands, and warmer nighttime temperatures contribute to greater sleep loss.
Q: Can losing a few minutes of sleep really matter?
Yes. Small nightly losses accumulate, leading to major annual declines in sleep and potentially higher health risks.
FAQs
How does climate change affect sleep?
Rising temperatures disrupt the body’s thermal regulation, leading to shorter and more fragmented sleep.
Are sleep disruptions harmful long-term?
Yes. Chronic poor sleep increases risks for heart disease, respiratory problems, and mental health conditions.
What data did researchers use?
Fitbit sleep data, demographic information, health records, and environmental temperature data from the All of Us Research Program.
Can policies reduce the impact of heat on sleep?
Improved housing design, urban cooling measures, and better access to air conditioning can help protect vulnerable populations.
Will sleep loss worsen as temperatures rise?
Researchers project significant annual sleep losses by 2099 unless effective interventions are implemented.
