Air pollution could affect your upper airways and increase your risk of sleep apnea, but other factors are likely also involved.
Scientists have long known about the effects that air pollution can have on our health, causing problems like respiratory and cardiovascular diseases.
In recent months, air pollution has been making headlines, first after wildfire smoke clouded San Francisco and this week after Thai authorities started to fire water cannons in the hopes of dispersing heavy smog.
Recently, new research has found that air pollution can do more than affect heart and lung health, it can hurt your sleep and impact your mood.
In a recent study published in the Annals of the American Thoracic Society, researchers looked at the link between obstructive sleep apnea and two common air pollutants — a type of fine particle pollution known as PM2.5 and nitrogen dioxide.
PM2.5 consists of particles that are 2.5 micrometers in diameter or smaller. These are produced by power plants, motor vehicles, burning wood, agricultural fires, and certain industrial processes.
To put this in perspective, dust, pollen and mold have a diameter of about 10 micrometers.
The authors of the study found that people who lived in areas with higher amounts of these two types of pollution were more likely to have obstructive sleep apnea.
Sleep apnea is a potentially serious sleep disorder in which breathing repeatedly stops and starts during sleep. Obstructive sleep apnea is the more common type. It occurs when the throat closes and blocks the flow of air.
In the study, the link between air pollution and sleep apnea still remained even after researchers took into account other factors that could affect the results, such as body mass index, high blood pressure, diabetes, smoking, and family income.
The study included 1,974 people who were enrolled in the Multi-Ethnic Study of Atherosclerosis (MESA). They also participated in the sleep and air pollution study.
Participants were a racially diverse group. But the average age was 68 years, so the findings may not apply to other age groups.
Researchers estimated the air pollution exposure at each person’s home using measurements taken in six U.S. cities.
The study was not a randomized, controlled trial, so it can’t show a cause-and-effect relationship between air pollution and sleep apnea.
Dr. Ryan Donald, a sleep medicine specialist at The Ohio State University Wexner Medical Center said this is an “interesting” area of study, but more research is needed.
Many factors contribute to sleep apnea. These would need to be considered in future studies — such as noise and light pollution, different types of sleep environments, stressors, and shape of the airway.
Likewise, seasonal variations in the link between air pollution and sleep apnea seen in some earlier studies may also be due to other factors.
“Air pollution can cause upper airway congestion,” said Donald, “but other things like pollen, mold spores and dust which cause allergies, can increase symptoms of sleep apnea.”
Many of these vary with the season.
Dr. Ray Casciari, a pulmonologist with St. Joseph Hospital in Orange, California, agreed that “further study is going to have to be done to investigate this,” but he said “the findings are not all that surprising.”
If pollution damages the mucous membranes of the nose and throat, it might contribute to sleep apnea, he said. Some studies have found a link between nasal congestion and sleep apnea.
Donald said another potential mechanism proposed by the authors “makes sense.”
“Different models, at least in animals, have found that air pollutants can cause some upper airway swelling and irritation,” said Donald.
This swelling could worsen sleep apnea, depending on where it’s located and how severe.
Casciari offered another possible mechanism — that air pollution might affect the brain directly to interfere with breathing during sleep.
He pointed to a recent study in China that found a link between exposure to air pollution and a drop in cognitive performance.
But even in that study, it’s not clear how — or if — air pollution could directly affect the brain.
Air pollution may even affect your mood.
“Pollution also has an emotional cost,” said lead researcher Siqi Zheng, the Faculty Director of MIT China Future City Lab, in a statement. “People are unhappy, and that means they may make irrational decisions.”
The researchers write that the effect of air pollution on mood may be partly due to direct physical effects, as well as the stress of trying to avoid the air pollution.
Researchers noticed this link was stronger in the cleanest and dirtiest cities. They suggest that the reason for this is that people who dislike air pollution move to cleaner cities, so their mood is more affected when the air is dirty.
On the other hand, people living in dirtier cities know about the long-term health effects of air pollution. So when the air is dirtier, they may become worried about its effect on their health.
Tiny particles coming from factories and fires aren’t the only type of air pollution that can affect your health.
Casciari said smoking and vaping sends chemicals and particulates directly to your lungs. This can be worse in some areas.
“If you smoke and you’re in a high-pollution area, you’re more likely to get lung disease and lung cancer than if you just were in a high-pollution area alone,” said Casciari.
There are also a variety of health conditions linked to air pollution with more years of research to back them up including heart disease, stroke, lung cancer, emergency room visits and hospital admissions, and early death.
Over the past few decades, the United States has made progress in reducing deaths caused by pollution.
A study published in October of last year found that air-pollution related deaths in the United States dropped from about 135,000 in 1990 to 71,000 in 2010.
“We have really done well in the United States with air pollution,” said Casciari. “The number of deaths from air pollution has dropped dramatically.”