Rising Temperatures Are Quietly Stealing Sleep From Millions of US Adults, According to New Research

Rising temperatures are no longer just about uncomfortable summers or record-breaking heatwaves. According to a major new study from researchers at the Keck School of Medicine of USC, warmer days and nights are now measurably cutting into how long — and how well — Americans sleep. The findings suggest that climate change may be shaping public health in ways many people have not fully considered yet, starting with something as fundamental as sleep.

The study, published in the journal Environment International, links higher outdoor temperatures to shorter sleep duration, poorer sleep quality, and more frequent nighttime disruptions. While the effects per night may seem small, the long-term consequences could add up to dozens of hours of lost sleep every year for the average adult by the end of the century.

How the Study Was Conducted

To understand how temperature affects sleep in real-world conditions, the research team analyzed data from 14,232 adults across the United States who are part of the All of Us Research Program, a large, long-term health initiative supported by the National Institutes of Health.

The data covered the years 2010 through 2022 and included an impressive more than 12 million nights of sleep data collected from wearable devices such as Fitbits. This allowed researchers to go far beyond self-reported sleep habits and look at objective sleep measurements, including:

Total sleep duration
Time taken to fall asleep
Sleep efficiency
Sleep stages such as deep sleep and REM sleep
Frequency of nighttime awakenings

In addition to sleep data, the researchers linked participants’ locations with meteorological records, enabling them to examine how daily and nighttime temperatures influenced sleep patterns.

What the Researchers Found About Temperature and Sleep

The results showed a clear and consistent relationship between higher temperatures and reduced sleep.

A 10-degree Celsius increase in daytime temperature was associated with an average loss of 2.19 minutes of sleep per night. Even more striking, a 10-degree Celsius increase in nighttime temperature led to a loss of 2.63 minutes of sleep per night.

While losing two or three minutes of sleep may not sound alarming at first, the researchers emphasized that this effect compounds over time and across populations. When multiplied over months, years, and millions of people, the total sleep loss becomes substantial.

Warmer Nights Are Especially Harmful

Nighttime heat appears to be particularly disruptive. The human body relies on a natural drop in core temperature to initiate and maintain sleep. When the surrounding environment stays warm, that cooling process becomes less efficient.

As a result, higher nighttime temperatures were linked not only to shorter sleep duration, but also to:

More frequent awakenings
Longer periods of wakefulness during the night
Lower sleep efficiency
Reduced time spent in deep sleep and REM sleep, both of which are crucial for physical and mental recovery

These changes can leave people feeling less rested even if they technically spend enough time in bed.

Certain Groups Are More Vulnerable Than Others

One of the most important contributions of this study is its detailed analysis of who is most affected by heat-related sleep loss.

The researchers found stronger effects among:

Women
People of Hispanic ethnicity
Individuals with chronic health conditions
Adults with lower socioeconomic status
People living in West Coast regions of the United States

The reasons for these differences are likely complex. Limited access to air conditioning, housing quality, occupational exposure, and pre-existing health conditions may all play a role. The findings suggest that heat-related sleep disruption is not evenly distributed and may worsen existing health and social inequalities.

Seasonal and Regional Differences Matter

Sleep loss linked to temperature was not uniform throughout the year. The strongest effects were observed during the summer months, from June through September, when sustained heat is more common.

Geography also played a significant role. People living in West Coast and marine climate regions experienced nearly three times as much sleep loss compared to those in other parts of the country. These areas often have cooler historical climates and lower rates of air conditioning, which may make residents more vulnerable to rising temperatures.

Projected Sleep Loss by the End of the Century

Using climate models and their observed data, the researchers estimated how future warming could affect sleep.

By the year 2099, adults in the United States could lose between 8.5 and 24 hours of sleep per year, depending on where they live and how temperatures continue to rise. This projection highlights how climate change may gradually reshape daily life in subtle but meaningful ways.

Why Sleep Loss Matters for Health

Sleep is deeply connected to nearly every aspect of health. Chronic sleep disruption has been linked to an increased risk of:

Cardiovascular disease
Respiratory problems
Metabolic disorders
Mental health conditions, including anxiety and depression

The researchers pointed out that extreme heat events are already known to increase deaths from heart and lung diseases. If rising temperatures also undermine sleep, they may further amplify these risks at a population level.

What Can Be Done to Protect Sleep in a Warming Climate

The findings point toward several possible interventions that could help reduce heat-related sleep loss, particularly for vulnerable populations.

Potential solutions include:

Expanding access to air conditioning, especially in high-risk regions
Improving building design, insulation, and ventilation
Promoting heat-resistant architecture through updated building codes
Increasing urban green spaces, tree cover, and green roofs to reduce local temperatures

The research team plans to study whether targeted interventions such as indoor cooling strategies, green infrastructure, and sleep hygiene programs can improve sleep and reduce heat-related health risks.

How Heat Disrupts the Biology of Sleep

From a biological perspective, sleep depends on a delicate balance between circadian rhythms and temperature regulation. As evening approaches, the body naturally lowers its core temperature to prepare for sleep.

When ambient temperatures remain high, this process is disrupted. Heat can also trigger stress responses in the body, increasing alertness and reducing the time spent in restorative sleep stages. Over time, repeated disruptions may contribute to chronic sleep problems.

A Growing Public Health Concern

This study adds to a growing body of evidence that climate change affects health in ways that extend beyond heatstroke and extreme weather. Sleep health may become an increasingly important, and often overlooked, dimension of climate-related risk.

By identifying who is most affected and how sleep is disrupted, the research provides valuable insight for policymakers, urban planners, and public health officials looking to adapt to a warming world.

Research paper:
Impact of heat exposure on sleep health and its population vulnerability in the United States – Environment International
https://doi.org/10.1016/j.envint.2025.109942