How air pollution increases heart attack, stroke risk Heavy smog hangs over Beijing's central business district, Feb. 22, 2013. ANN ARBOR, Mich., April 25 (UPI) -- Long-term exposure to air pollution speeds up atherosclerosis, or "hardening of the arteries," and increases the risk of heart attack, U.S. researchers say. Study leader Sara Adar of the University of Michigan School of Public Health and Joel Kaufman of the University of Washington, found higher concentrations of fine particulate air pollution were linked to a faster thickening of the inner two layers of the common carotid artery -- a blood vessel that provides blood to the head, neck and brain. Conversely, the researchers found reductions of fine particulate air pollution over time were linked to slower progression of the blood vessel thickness. The thickness of carotid artery layers is an indicator of how much atherosclerosis is present in arteries throughout the body, even among people with no obvious symptoms of heart disease, Adar said. "Our findings help us to understand how it is that exposures to air pollution may cause the increases in heart attacks and strokes observed by other studies," Adar said in a statement. The researchers tracked 5,362 people ages 45-84 from six U.S. metropolitan areas as part of the Multi-Ethnic Study of Atherosclerosis and Air Pollution. Their research was published in the journal PLOS Medicine.