Rising heat is causing millions of people to lose sleep

New research points to a strong link between hot nights and poor sleep. The study helps explain how rising temperatures disturb rest and why some groups face stronger effects.

Researchers used long-term sleep records from the All of Us program. These records show clear connections between hotter air, lighter sleep, more waking, and personal factors such as age, income, or health.

The findings matter for communities across the country. Hotter nights may lead to wider sleep problems in the future, and public health may shift as a result.

Hot nights hurt sleep

Hot nights reduce sleep for many groups. People with long-term health problems or low income lose even more rest.

Warm air prevents the body from cooling enough for natural sleep. Hot conditions raise stress and interrupt normal sleep cycles. Deep sleep becomes shorter, and REM sleep also drops.

People wake up more often and stay awake longer, which reduces overall rest and makes nights feel less refreshing.

More heat, less sleep

Study lead author Dr. Jiawen Liao is an expert in the Keck School of Medicine at the University of Southern California (USC).

“We already know that when there are extreme heat events, more people die from cardiovascular disease and pulmonary disease,” said Dr. Liao. “What will this mean for population health as global temperatures continue to rise?”

The All of Us wearable data offer millions of nights of measurements. Patterns reveal clear reductions in total sleep time with every jump in temperature anomalies.

The researchers found that a 10-degree nighttime temperature increase was linked to an average sleep loss of 2.63 minutes. 

“This may seem like a small amount, but when it adds up across millions of people, the total impact is enormous,” said Dr. Liao.

Heat affects all sleep stages

Heat changes more than how long people sleep. Warm nights break the normal rhythm of rest. People wake up more, sleep feels less steady, and sleep starts later.

All sleep stages become shorter, including light, deep, and REM sleep. These cuts can affect heart health, thinking, and mood over time. Frequent sleep breaks add stress to the body.

Some regions face stronger problems. Marine zones on the West Coast lose more sleep because many homes use less air conditioning.

Summer months bring the steepest declines in rest. Late spring and early fall also show clear reductions.

Who loses the most sleep

Vulnerability does not spread evenly across the map. Middle-aged adults show sharper declines in rest. Female participants show larger losses than male participants.

Hispanic groups experience stronger disruptions than non Hispanic groups. Lower income households, renters, and single adults show deeper losses compared with higher income homeowners and partnered adults.

Chronic conditions increase sensitivity as well. Cardiovascular disease, depression, and obesity appear to amplify sleep loss under higher heat exposure. Wearable records show stronger disruptions for individuals living with those conditions.

Personal living environments also matter. Rental units often have weaker insulation and fewer cooling options, which raises exposure to warm night air. Limited green space compounds heat buildup in many urban settings.

Future projections vary across regions

Climate models paired with sleep data offer a preview of future patterns. Projections across decades suggest additional sleep loss piling up each year as heat intensifies.

Hot zones, cold zones, mixed zones, and marine zones face distinct trajectories. Marine zones show the highest projected losses by the end of the century.

Annual sleep losses could reach several hours per person under high-emission scenarios. On peak summer days, the nightly deficit may rise to levels that noticeably impair mental clarity, mood stability, and long-term health.

Protecting sleep from heat

Researchers highlight clear paths for future work. Cooling strategies, stronger building standards, and wider access to green roofs or urban vegetation could reduce exposure.

Indoor cooling interventions may support healthier sleep patterns during warm seasons. Public policy may also prioritize communities with lower resources and higher documented risks.

“If we can help people sleep better, we may be able to reduce illness and save lives,” said Dr. Liao.

The study is published in the journal Environment International.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–