In a new study published in the Annals of the American Thoracic Society, researchers from the University of Washington, Harvard University and Columbia University report a link between obstructive sleep apnea and increases in two of the most common air pollutants: fine particulate pollution (PM_2.5) and nitrogen dioxide (NO₂), a traffic-related pollutant.

According to the Mayo Clinic, sleep apnea is a potentially serious sleep disorder in which breathing repeatedly stops and starts.

Sleep disruption and obstructive sleep apnea (OSA) are associated with hypertension, diabetes, stroke, ischemic heart disease, cancer, and cardiac death. Proposed mechanisms include altered autonomic tone, increased inflammation and metabolic dysregulation. Similarly, air pollution has been linked with cerebrovascular disease, cancer and cardiovascular morbidity and overall mortality, attributed in part to an increased systemic inflammatory response to fine particles. Ambient air pollution consists of fine particulate matter as well as gaseous products of combustion (oxides of nitrogen), produced through burning fossil fuels from automobiles emissions to power plants. Although there is increasing interest in the influence of the environment on sleep, there is limited research evaluating the relationship between sleep and air pollution.

—Billings et al.

Prior studies have shown that air pollution impacts lung and heart health, but only a few studies have looked at how air pollution might affect sleep. It seemed likely that air pollution was detrimental to sleep, given that air pollution causes upper airway irritation, swelling and congestion, and may also affect the parts of the brain and central nervous system that control breathing patterns and sleep.

—Dr. Martha Billings, lead study author and associate professor of medicine at the University of Washington

The researchers analyzed data from 1,974 participants in the Multi-Ethnic Study of Atherosclerosis (MESA) who also enrolled in both MESA’s Sleep and Air Pollution studies. (MESA is a longitudinal study of cardiovascular disease among adults aged 45-84 years.) The participants (average age 68) were a diverse group: 36% were white, 28% black, 24% Hispanic and 12% Asian. Nearly half (48%) of the participants had sleep apnea.

Using air pollution measurements gathered from hundreds of MESA Air and Environmental Protection Agency monitoring sites in six US cities, plus local environment features and sophisticated statistical tools, the research team was able to estimate air pollution exposures at each participant’s home.

The study found a participant’s odds of having sleep apnea increased by:

• 60% for each 5 micrograms per cubic meter (μg/m³) increase in yearly PM_2.5 exposure; and

• 39% for each 10 parts per billion increase in yearly NO₂.

The researchers adjusted their findings for factors that may have biased their results, including body mass index, family income, diabetes, high blood pressure, smoking and the social economic status of the neighborhood in which participants lived.

The researchers also looked at sleep efficiency—the percentage of time in bed spent actually asleep compared to total time in bed—using a device called a wrist actigraph that measures small movements. They did not find an association between air pollution and sleep efficiency when they adjusted for those same factors.

Because the study was not a randomized, controlled trial, it cannot prove a cause and effect relationship between air pollution and sleep apnea. The researchers said another study limitation was that they could not adjust their findings for noise and light pollution, which may affect sleep.

This study demonstrates an association of ambient air pollution exposure with sleep apnea. Chronic exposure to greater levels of air pollution may adversely influence breathing during sleep, suggesting possible etiologies of sleep health disparities. Future studies are needed to discern the effects of specific air pollutants from other neighborhood and regional features, to explore possible mechanisms, and to evaluate if improving air quality improves sleep health.

—Billings et al.

Resources

• Martha E Billings, Diane Gold, Adam Szpiro, Carrie P Aaron, Neal Jorgensen, Amanda Gassett, Peter J Leary, Joel D. Kaufman, Susan R Redline (2018) “The Association of Ambient Air Pollution with Sleep Apnea: The Multi-Ethnic Study of Atherosclerosis” Annals ATS doi: 10.1513/AnnalsATS.201804-248OC