There’s 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 researcher at Flinders University investigating the subject.
At the same time, sleep apnea is already expected to become a growing problem for those living in cities, due to the chronic impact of air pollution on nighttime breathing, something which is only predicted to get worse. Last year, Hong Kong researchers led a study where they found that both short and long-term exposure to PM2.5 particles—tiny airborne particles, less than 2.5 micrometers wide, which are generated by sources such as vehicle exhausts, factory emissions, and wildfires 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 for people with existing sleep apnea.
“Obstructive sleep apnea occurs when the upper airway becomes unstable and collapses during sleep,” says Martino Pengo, associate professor from the University of Milano-Bicocca who studies the subject. “Air pollutants can increase this instability by irritating the tissues of the throat, making the airway narrower and more prone to collapse when muscle tone naturally falls at night. Nitrogen dioxide is a strong airway irritant and may promote local inflammation that can fragment sleep and destabilize breathing.”
While concerning, such research also points to possible ways of mitigating risk. Martha Billings, professor of medicine in the University of Washington’s division of pulmonary, critical care, and sleep medicine advises using indoor air filtering devices if online air quality databases show that your city ranks particularly poorly. “I would recommend it especially if the air quality index is greater than 200 as can happen with forest fires or other stagnant air,” she says.
Likewise with rising temperatures, losing weight could be a way of mitigating your sleep apnea risk. Research has highlighted how those who are overweight or obese are more at risk of experiencing more severe episodes of sleep apnea in hot weather, with their breathing stopping and starting more often during the night. Pinilla says this relates to how accumulating body fat alters the body’s internal temperature regulation. “People with higher fat mass tend to retain more heat, and dissipate it less efficiently making it harder to maintain a comfortable core temperature at night,” she says. “On hot nights, this can lead to lighter and more fragmented sleep.”
Men, who are more vulnerable to sleep apnea anyway as they are more prone to accumulating fat in the neck and have a longer and more collapsible upper airway, are particularly at risk, as are those with preexisting mental health or sleep disorders.
The Flinders team is hoping to ultimately be able to develop personalized advice and heat-warning systems for those who are at greater risk of experiencing sleep apnea events during heatwaves, as well as simple solutions which anyone can turn to. They are hoping to gain funding to be able to run experiments where people receive cooling mattress toppers or follow specific behavioral advice, such as ensuring they are well hydrated when going to bed, to see if this can actively prevent apnea events in warmer weather.
“Ultimately, our goal is to develop practical, evidence-based recommendations that can be applied during heat waves, particularly for vulnerable groups and people at higher risk,” says Pinilla.
