Fine particulate air pollution from fossil fuel-burning cars and other sources can thicken the lining of the carotid artery, leading to an increased risk of heart disease and stroke, according to a long-term study published today in PLOS Medicine.
The 10-year longitudinal study, called MESA Air (Multi-Ethnic Study of Atherosclerosis and Air Pollution), followed 5,362 people ages 45 to 84 living in six U.S. communities: Baltimore, Chicago, Los Angeles, New York, St. Paul, and Winston-Salem. Participants were from varied ethnic backgrounds and none had been previously diagnosed with cardiovascular disease, or CVD.
Data collected in 2.5-year intervals beginning in 2000 showed that participants who were exposed to higher concentrations of fine particulate air pollution experienced more rapid thickening of the inner wall of the carotid artery, a major blood vessel that supplies blood to the head, neck, and brain.
The thickness of the carotid artery is an indicator of how much plaque has built up in blood vessels throughout the body, and is a common marker of CVD. Intima-media thickness, or IMT, is a measurement of the thickness of the inner layers of artery walls.
The researchers measured indoor and outdoor pollution levels and IMT progression, comparing people who lived in highly polluted urban environments to others residing in more rural, less polluted areas.
“We see that even within the same metropolitan areas, people living in the more polluted sections of town have faster rates of progression of IMT than those in the cleaner parts of town,” said study co-author Sara Adar, an Assistant Professor of Epidemiology at the University of Michigan School of Public Health, in an interview with Healthline.
Although the observed changes in patients' artery walls were smaller than the width of a human hair, the accelerated progression of IMT in individuals living in more polluted areas translates into a two percent greater risk of stroke.
The MESA Air study findings support previous research documenting a higher risk of mortality and cardiovascular disease among people with greater long-term exposure to air pollution.
“These studies include the seminal Harvard Six City study, which found that persons in the highly polluted Steubenville, Ohio, had 26 percent higher mortality rates than persons with low-pollution exposure in Portage, Wisconsin, even after control for smoking and other risk factors,” Adar noted.
Living in a Cleaner Environment May Decrease Your CVD Risk
Interestingly, the MESA Air study also found that improvements in air quality were linked to slower IMT progression.
“These findings bolster recent reports that falling pollution levels in the United States after the adoption of the Clean Air Act are associated with reduced mortality and increased life expectancy,” said Adar.
When asked if there is a safe threshold for air pollution, Adar said, “Although our mean long-term concentrations were slightly above the new annual average U.S. National Ambient Air Quality Standard and the World Health Organization guidelines, our findings are expected to hold even at lower concentrations, as past evidence suggests that there is likely no safe threshold for air pollution.”
Future Findings from the MESA Air Study
The paper published today is an interim report based on the study's first three examination periods. Future analyses will include the full 10 years of follow-up data and incorporate more refined exposure estimates that account for how much outdoor air pollution ends up in our homes and how much time people spend indoors versus outdoors.
The MESA Air study was supported by awards from the Environmental Protection Agency (EPA); the National Heart, Lung, and Blood Institute (NHLBI); and the National Institute of Environmental Health Sciences (NIEHS). The funders did not influence the study design, analysis, or reporting.