Living in polluted areas may accelerate the narrowing of arteries, according to researchers from the Keck School of Medicine of USC.

A team of environmental health experts, cardiologists and other investigators have released initial results of their ongoing studies on air pollution and cardiovascular disease at the American Heart Association’s Scientific Sessions in New Orleans.

The researchers looked at the relationship between the wall thickness of study participants’ neck arteries and the levels of certain air pollutants in the participants’ neighborhoods.

Scientists found that artery wall thickness rose as levels of pollution increased.

“These findings suggest that exposure to air pollutants may play an important role in the development of cardiovascular disease,” said Kenneth Olden, director of the National Institute of Environmental Health Sciences (NIEHS), a federal agency that funded the project.

“We already know that higher artery wall thickness is associated with a higher risk of heart attacks and stroke later in life,” Olden said.

Nino Kuenzli, associate professor of preventive medicine in the Keck School and initiator and principal investigator of the project, noted that researchers must corroborate the findings in other populations.

“If confirmed, the public health relevance would be enormous,” he said. “Atherosclerosis plays a major role in a broad array of diseases, and almost everybody is regularly exposed to ambient air pollution, 24 hours a day, over a lifetime.”

Kuenzli and his colleagues reviewed data from two clinical trials on 798 people age 40 or older who lived in the Los Angeles area. That data included measurements of the thickness of the inner lining of their carotid artery walls. This is called carotid artery intima-media thickness, or CIMT which is measured by ultrasound.

Researchers use CIMT as a way to assess the progression of atherosclerosis, the build-up of fatty material along inner artery walls.

The researchers then determined the levels of certain airborne particulate matter typically found in each participant’s neighborhood. These particles are pollutants with a diameter of 2.5 micrometers or less – smaller than the width of a human hair – and are tiny enough to be inhaled into the smallest of airways. They come from tailpipe emissions and other fossil fuel-burning activities.

Particulate matter levels varied from 5.2 micrograms per cubic meter (µg/m3) to 26.9 µg/m3, depending on the neighborhood.

The researchers found that for every increase of 10 µg/m3 in these particulates, CIMT increased by 5.9 percent. After adjusting for age, demographic, lifestyle (including active and passive smoking) and physiologic factors, researchers found that each 10 µg/m3 increase in particulates accounted for a 3.9 percent to 4.3 percent rise in CIMT.

Air pollution and CIMT were even more strongly associated in people over age 60 and those taking cholesterol-lowering medications.

Atherosclerosis is thought to be an inflammatory process. Mounting evidence shows that pollutants contribute to inflammation in the lung and cardiovascular system. Much further research is needed to clarify the underlying mechanisms of these findings.

Atherosclerotic plaques can grow large enough to choke off blood flow through an artery. Or, more often, the plaques can rupture. These plaques can lead to blood clots that break off and travel down the bloodstream, getting stuck in another artery.

If they block a blood vessel that feeds the heart, it causes a heart attack; when they block a blood vessel that feeds the brain, it causes a stroke. Moreover, higher CIMT is associated with heart attacks and stroke later in life.

Prevention techniques focus on influencing risk factors. These strategies include lowering cholesterol levels, avoiding smoking and losing weight, among others. If these novel findings can be confirmed in other studies, clean air policies may be added to the list of atherosclerosis preventing strategies.

Support for this research came from the Southern California Environmental Health Sciences Center, funded by the NIEHS, and the National Institute on Aging.