Rising nighttime temperatures worsen sleep and sleep apnea
STUDY: Krčum J et al, Clocks & Sleep 2026
STUDY TYPE: Scoping review
FUNDING: Ministry of Science, Innovation and Technological Development of Serbia
Background
As nights get hotter, sleep quality suffers, and older adults lose the ability to cool down efficiently. Aging blunts sweating and skin blood flow, both needed to drop core body temperature enough to fall and stay asleep.
The Review
- 31 studies across six continents, spanning objective, subjective, and lab-based sleep measures in adults 45 and up.
- No single control group. Most studies compared sleep on hot versus cooler nights within the same people.
- Outcomes included total sleep time, sleep efficiency, sleep architecture, and sleep apnea severity.
Sleep Quality
Heat consistently shortened sleep. Total sleep time dropped 10 to 45 minutes on hot nights, and sleep efficiency fell 5 to 15%.
One 12-month study of older adults found the sweet spot for sleep sits between 20 and 25 degrees Celsius (68 to 77°F); above 25°C, sleep efficiency dropped and total sleep time fell by about an hour at 30°C compared with 22°C. In line with these temperatures, sleep doctors recommend 65-70°F at night for insomnia.
Sleep quality is lighter and REM sleep melts in the heat. Raising bedroom temperature from 27°C to 30°C reduced REM sleep by 5 minutes and added 27 minutes of nighttime wakefulness in adults over 65 (in a lab study). Adding a fan recovered some of that lost deep and REM sleep, even without air conditioning.
Sleep Apnea
Hotter nights worsened sleep apnea in two large wearable-based studies. Each 10°C rise in temperature raised the odds of an apnea flare by 8.4%. The hottest nights nearly doubled the risk of apnea compared with the coolest nights.
Who is at Risk
Women, older adults, low-income patients, and those with chronic disease fared worst. Air conditioning and simple ventilation blunted much of the damage, but access to cooling was uneven.
Though not included in the review, antipsychotics and anticholinergics might worsen these problems by impairing temperature regulation.
Practice Implications
- Look for worsening sleep, and sleep apnea, during heat waves.
- Cooler bedrooms, and even a low-cost fan, can deepen sleep.
- A cool shower may help just before bed, but a hot bath 2-3 hours before bed is a proven. It raises body temperature, which then lowers after the bath, and the lowering deepens sleep. Caution: it can cause hypotension and falls when getting out of the bath, and don’t stay in the bath for longer than 20 minutes to avoid skin problems.
—Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
