High temperatures negatively affect sleep health

There is also the physiological effect of heat itself on our breathing. “Heat may also destabilize breathing control, increase fluid retention, and promote dehydration, all of which can make the upper airway more collapsible and increase the likelihood of sleep apnea,” says Lucia Pinilla, another Flinders University researcher studying the topic.

Meanwhile, sleep apnea is already expected to become a growing problem for those living in cities, due to the chronic impact of air pollution on night-time breathing, which is expected to get worse. Last year, researchers from Hong Kong led a study in which they found that short- and long-term exposure to PM2.5 particles — tiny airborne particles, less than 2.5 micrometers across, that are generated by sources such as automobile exhaust, factory emissions, and forest fires, and can penetrate deep into the lungs and bloodstream — makes sleep apnea more likely.

Others have shown that the same is true for nitrogen dioxide, a reddish-brown gas released into the air from exhausts, power plants and other industrial facilities, while exposure to pollution also worsens symptoms in people with sleep apnea.

“Obstructive sleep apnea occurs when the upper airway becomes unstable and collapses during sleep,” says Martino Pingo, an associate professor from the University of Milan-Bicocca who studies the topic. “Air pollutants can increase this instability by irritating throat tissue, making the airway narrower and more likely to collapse when muscle tone naturally decreases at night. Nitrogen dioxide is a powerful airway irritant and may promote local inflammation that can lead to sleep fragmentation and destabilization of breathing.”

Although worrying, this research also points to possible ways to mitigate risks. Martha Billings, MD, professor of medicine in the Department of Pulmonary, Critical Care and Sleep Medicine at the University of Washington, recommends using indoor air purifiers if online air quality databases show your city ranks particularly poorly. “I recommend it especially if the air quality index is greater than 200 as can happen with wildfires or other stagnant air,” she says.

As with rising temperatures, losing weight can be a way to mitigate the risk of sleep apnea. Research has highlighted that people who are overweight or obese are more at risk of experiencing more severe episodes of sleep apnea in hot weather, with breathing stopping and starting more often during the night. This is related to how body fat accumulation affects the regulation of the body’s internal temperature, Pinilla says. “People with higher fat mass tend to retain more heat and dissipate it less efficiently, making it difficult to maintain a comfortable core temperature at night,” she says. “On hot nights, this can lead to lighter, more fragmented sleep.”

Men, who are more susceptible to sleep apnea anyway because they are more likely to accumulate fat in the neck and have a longer, more collapsible upper airway, are particularly at risk, as are those with pre-existing mental health or sleep disorders.

Flinders’ team hopes to eventually develop personalized advice and heat warning systems for those who are most at risk of developing sleep apnea during heatwaves, as well as simple solutions that anyone can use. They are hoping to secure funding so they can run trials where people receive cooling mattress covers or follow specific behavioral tips, such as making sure they are well hydrated when going to bed, to see if this can effectively prevent apnea in warm weather.

“Ultimately, our goal is to develop practical, evidence-based recommendations that can be applied during heatwaves, especially for vulnerable groups and people most at risk,” Pinilla says.