While many studies have found associations between long-term exposure to ambient air pollution and cardiovascular disease and death, a new study published in Environmental Health Perspectives provides the first epidemiological evidence of an association between atherosclerosis and exposure to ambient PM_2.5.

Atherosclerosis is a type of arteriosclerosis (hardening of the arteries). Atherosclerosis is the term for the process of fatty substances, cholesterol, cellular waste products, calcium and fibrin (a clotting material in the blood) building up in the inner lining of an artery. The resulting buildup is called plaque, and is a primary mechanism underlying heart attack and stroke.

This study, in other words, finds a direct association of pollution with the incidence of the disease/death mechanism.

The researchers used the thickness of the carotid artery (carotid artery intima-media thickness (CIMT) is a well-established quantitative measure of generalized atherosclerosis) to assess the association with ambient residential levels of  PM_2.5.

Results showed variation across groups, but a combined average 4.4% thickening associated with residential concentrations of 10 µg/m3 PM_2.5. Results were much worse in women over age 60. The chart to the right depicts the results of the different groups. (Click to enlarge.)

To put that in perspective, the thickening resulting from PM exposure is approximately the same—and higher in some groups—as that caused by secondary tobacco smoke (ETS—Environmental Tobacco Smoke).

The authors are careful to point out that PM is probably serving as a surrogate for the mixture of urban air pollution and constituents of PM—i.e., there is likely more at work than simply PM, and that atherosclerosis results from complex processes that may include a combination of various urban pollutants, host factors, and pathways.

The finding of the larger association, however, is an important one for policy and public health—especially given the rapid growth in diesel use in various parts of the world.