Higher nighttime temperatures are linked to shorter sleep times and lower sleep quality, especially for people with chronic health conditions, lower socioeconomic status, or those living on the West Coast, according to a new USC study. Researchers estimate that by 2099, people could lose up to 24 hours of sleep each year due to heat, highlighting the potential impact of climate change on sleep health. The findings were just published in the journal Environment International .
Warm weather can disturb sleep in several ways, including by preventing the body from cooling down, triggering a stress response, and reducing time spent in deep sleep and rapid eye movement (REM) sleep. Poor sleep can in turn increase risk for a number of health problems, including heart and respiratory issues and mental health concerns.
"We already know that when there are extreme heat events, more people die from cardiovascular disease and pulmonary disease. What will this mean for population health as global temperatures continue to rise?" 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.
Past research has documented the link between rising temperatures and sleep problems, but most studies lacked details on the demographics, socioeconomic, and health information of participants. That prevented researchers from gaining a full understanding of who is most at risk and how best to respond.
The new study, done in collaboration with Harvard Medical School/Brigham and Women's Hospital and funded in part by the National Institutes of Health, leverages data from 14,232 U.S. adults in the All of Us Research Program to begin filling in those gaps. All of Us is a longitudinal study that includes detailed data from surveys, health records, wearable devices and other sources.
"This work is an important step toward understanding how sleep is affected by environmental stressors like heat, which can increase the risk of disease and even death," Liao said. "If we can help people sleep better, we may be able to reduce illness and save lives."
Warmer nights, shorter sleep
The researchers obtained data on U.S. adults enrolled in All of Us that was collected between 2010 and 2022. Along with detailed demographic, socioeconomic and health information, participants also shared their FitBit data, giving the research team a rich picture of sleep patterns.
In total, the researchers analyzed more than 12 million nights of sleep, looking at how long people slept and how easily they fell asleep. They also examined 8 million nights of data on sleep stages and how often sleep was interrupted. Finally, they used location and meteorological data to find out whether sleep patterns were linked to changing temperatures.
They found that a 10-degree Celsius increase in daytime temperature was associated with 2.19 minutes of lost sleep, while a 10-degree nighttime temperature increase was associated with a loss of 2.63 minutes. The effects were greater among females, people of Hispanic ethnicity, people with chronic diseases, and those with a lower socioeconomic status.
"This may seem like a small amount, but when it adds up across millions of people, the total impact is enormous," Liao said.
The researchers also found that effects differed by season, with more sleep loss occurring from June to September, and geographic region, with people in West Coast areas losing nearly three times as much sleep as people in other regions. Based on the findings, the researchers project that U.S. adults could lose between 8.5 and 24 hours of sleep per year by 2099, depending on their location.
In addition to shorter sleep times, rising temperatures were also associated with more disrupted sleep throughout the night and more time spent awake in bed.
Improving sleep and health
A key takeaway from the study is that some populations face higher risks than others. Targeting interventions and policy changes to those groups may be particularly impactful, Liao said.
For example, policymakers in West Coast regions could promote access to air conditioning, expand green roofs or increase urban green space. Building codes that require better insulation, improved ventilation or heat-resistant design could also be strengthened in these areas to protect population health.
Next, Liao and his colleagues plan to explore whether interventions designed to improve sleep, such as indoor cooling, green roof or sleep hygiene programs, can help reduce the harmful effects of heat exposure. They aim to test whether improving sleep through these interventions can reduce heat-related health problems and lower the risk of disease and death.
About this study
In addition to Liao, the study's other authors are Rima Habre, Erika Garcia, Sandrah P. Eckel, Megan M Herting, Wu Chen, Chenyu Qiu, Zhenchun Yang, Rob McConnell, Frank Gilliland and Zhanghua Chen from the Department of Population and Public Health Sciences, Keck School of Medicine of USC, University of Southern California; Joe Kossowsky from Boston Children's Hospital and Harvard Medical School, Boston, Massachusetts; and Susan Redline from Harvard Medical School and Brigham and Women's Hospital, Boston, Massachusetts.
This work was supported by the National Institutes of Health [R01ES033707, P30ES007048]. Jiawen Liao is also supported by the GeoCAFE Scholar Program with grant 2427815 from the National Science Foundation and CAFE Research Coordinating Center of the NIH Climate Change and Health Initiative [NIH U24ES035309].
