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. This review looks at those effects in older adults (45+). Aging blunts sweating and skin blood flow, both of which are needed to lower core body temperature to induce sleep.
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 age, 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.
A Hot Bath or Cold Shower?
[Dr. Aiken’s Addendum]
A cold shower before bed sounds like an intuitive fix, but a hot bath a few hours earlier may work better.
In the 1990’s, sleep researchers discovered they could lower core body temperature and deepen sleep with a 20 minute hot bath 2-3 hours before bed. It worked in small trials, most of which involved women over 50.
There are a few cautions, so read the description carefully.
- It can cause falls by lowering blood pressure
- Limit to 20 minutes to avoid skin problems
- Don’t use if pregnant, planning pregnancy, or have skin disorders
I tried the hot-bath technique before and can report:
- It is difficult to set in hot water that long — my heart raced like aerobic exercise
- I slept deeper that night than ever before, and felt a lot cooler the next day
A weekly hot bath also has evidence to treat depression.
Practice Implications
- Look for worsening sleep, and sleep apnea, during heat waves.
- Cooler bedrooms, and even a low-cost fan, can deepen sleep.
- A hot bath also works, but is not without risks.
—Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
