Study Identifies Mechanism that Links Air Pollution to Heart Disease

Long-term exposure to air pollution—especially motor vehicle traffic-related pollution—has been associated with an increased risk of cardiovascular-related events and mortality. But previous studies have fallen short when it comes to identifying the biological mechanisms by which air pollution leads to cardiovascular disease and determining the level of air pollution that is considered unsafe.

The Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air Pollution) found that as exposure to traffic-related air pollution increases, so does the amount of calcium deposited in the coronary arteries. Looking at the buildup of coronary arterial calcium is a direct way to measure atherosclerosis in the heart, which leads to heart attacks.

“The study provides important new information on how pollution affects the main biological process that leads to heart disease,” says Joel Kaufman, MD, a University of Washington professor of environmental and occupational health sciences, epidemiology, and medicine who led the study.

“The results show that differences in the levels of environmental air pollution in the U.S., which has relatively good environmental air quality compared to many parts of the world, are associated with the development and progression of coronary artery calcium deposits,” says R. Graham Barr, MD, DrPH, professor of medicine and epidemiology at Columbia University Medical Center and an author of the paper, which was published online in The Lancet. “Since coronary artery calcium is predictive of cardiovascular-related events and mortality, this study offers compelling evidence that stricter controls may be warranted, even in the U.S.”

MESA Air Pollution, an observational study that recruited nearly 7,000 healthy participants in Baltimore, Chicago, Los Angeles, New York City, St. Paul, and Winston-Salem, sought to address shortcomings of earlier research. Over 10 years, researchers from several institutions, including Columbia, periodically examined the recruits for signs of cardiovascular disease. The participants underwent CT scans to measure coronary artery calcium deposits, a measure of atherosclerosis.

In addition, the researchers meticulously calculated each participant’s exposure to outdoor air pollutants that are abundant in high-traffic areas, including ambient fine particulate matter smaller than 2.5 microns (PM_2.5), nitrogen oxide (NO_x), nitrogen dioxide (NO₂), and black carbon (soot). The measurements were taken at 27 long-term sites, 771 community snapshot locations, and outside nearly 700 of the participants’ homes.

Depending on where they lived, the study participants were routinely exposed to concentrations between 9.2 and 22.6 µg/m³. Currently, the United States mandates an annual average PM_2.5 concentration of 12 µg/m³.

The research team found that every 5 µg/m³ higher concentration of fine particulate matter, or 35 parts per billion higher concentration of NO_x and NO₂, was associated with a 20 percent increase in calcium deposits.

In a commentary also published online in The Lancet, Professor Bert Brunekreef of the University Medical Center Utretcht, Netherlands, and Professor Barbara Hoffman of the University of Dusseldorf, Germany, note that it was “sobering” to learn that there was no threshold below which the effects of fine particulate matter did not have an impact on coronary artery calcium deposition.

Further details about the study may be found in this article.