Now, direct evidence from the Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air), a 10-year epidemiological study of 6,795 people aged 45–84 years from six US states, shows that air pollution—even at levels below regulatory standards—accelerates the progression of atherosclerosis. The condition, also called hardening of the arteries, can cause heart attacks.

Repeated scans were done for nearly all participants between 2002 and 2005; for a subset of participants between 2005 and 2007; and for half of all participants between 2010 and 2012. Common carotid artery intima-media thickness (a measurement of the thickness of tunica intima and tunica media, the innermost two layers of the wall of an artery) was measured by ultrasound in all participants at baseline and in 2010–12 for 3,459 participants.

Residence-specific spatio-temporal pollution concentration models, incorporating community-specific measurements, agency monitoring data, and geographical predictors, estimated concentrations of PM_2.5 and NO_x between 1999 and 2012.

The researchers found that coronary calcium in the subject population increased on average by 24 Agatston units (a measure of calcium generally included in the results from a CT Test for Coronary Calcification) per year (SD 58), and intima-media thickness by 12 μm per year, before adjusting for risk factors or air pollutant exposures.

Participant-specific pollutant concentrations averaged over the years 2000–10 ranged from 9.2–22.6 μg PM_2.5/m³ and 7.2–139.2 parts per billion (ppb) NO_x. For each 5 μg PM_2.5/m³ increase, coronary calcium progressed by 4.1 Agatston units per year (95% CI 1.4–6.8) and for each 40 ppb NO_x coronary calcium progressed by 4.8 Agatston units per year (0.9–8.7)—about a 20% acceleration in the rate of these calcium deposits.

This was the most in-depth study of air pollution exposures ever applied to a large study group specifically designed to examine influences on cardiovascular health. The study provides important new information on how pollution affects the main biological process that leads to heart disease. The evidence supports worldwide efforts to reduce exposures to ambient air pollutants.

—lead author Dr. Joel Kaufman

The effects were seen even in the United States where efforts to reduce exposure have been notably successful compared with many other parts of the world, Dr. Kaufman noted. Exposures were low when compared to US ambient air quality standards, which permit an annual average PM_2.5 concentration of 12 µg/m³. (As noted above, the participants in this MESA-Air study experienced concentrations between 9.2 and 22.6 µg/m³.)

In an accompanying editorial in The Lancet, Dr. Bert Brunekreef, a professor at Utrecht University in The Netherlands, and Dr. Barbara Hoffmann, a professor of the University of Düsseldorf in Germany, described the study as “exemplary.” Noting that the results are sobering, they called for decisive action in controlling pollution levels worldwide.

The MESA Air study was funded in 2004 by the US Environmental Protection Agency (EPA). The project involved researchers at a number of institutions, and characterized air pollutant exposures experienced by people in the National Heart, Lung, and Blood Institute’s Multi-Ethnic Study of Atherosclerosis (MESA). The participants lived in six major cities across the United States. The clinics were in Baltimore, Chicago, Los Angeles, New York City, St. Paul and Winston-Salem. Of the people in the study, 39% were white, 27% black, 22% Hispanic, and 12% Chinese.

The authors come from institutions that include the University of Washington, Columbia University, University of California, Los Angeles; Wake Forest University, Northwestern University, Johns Hopkins University, University of Michigan, University of Vermont, University of Minnesota, and University of Wisconsin, among others.

Resources

• Kaufman, Joel D et al. (2016) “Association between air pollution and coronary artery calcification within six metropolitan areas in the USA (the Multi-Ethnic Study of Atherosclerosis and Air Pollution): a longitudinal cohort study” The Lancet doi: 10.1016/S0140-6736(16)30375-0