New findings indicate that smog, which largely consists of ambient ozone, may lead to atherosclerosis, a cardiovascular condition.
Over time, the buildup of plaque inside the blood vessels' walls thickens the arteries, which restricts the blood, nutrients, and oxygen that would normally reach the rest of the body.
While researchers do not yet know what triggers atherosclerosis, factors such as high blood pressure, high cholesterol, and cigarette smoking are believed to cause much of the damage.
New research points the finger at another possible culprit: air pollution. Meng Wang, Ph.D., an assistant professor of epidemiology and environmental health at the University at Buffalo School of Public Health and Health Professions in New York, is the lead author of the study.
Wang and the team published their findings in the journal Environmental Health Perspectives.
Ozone exposure and atherosclerosis
Wang and colleagues clinically followed 6,619 adults, who were 45–84 years old and who did not have cardiovascular disease or any other conditions at the start of the study.
They followed the participants for a mean period of 6.5 years, as part of the Multi-Ethnic Study of Atherosclerosis in which the participants had enrolled. They came from six cities across the United States: Winston-Salem, NC; New York City, NY; Baltimore, MD; St. Paul, MN; Chicago, IL; and Los Angeles, CA.
"We used statistical models to capture whether there are significant associations between ozone exposure and [atherosclerosis]," explains Wang.
"[The model] suggests that there is an association between long-term exposure to ozone and progression of atherosclerosis," he goes on to report.
Specifically, the study found an association between chronic ozone exposure and an "increased rate of carotid wall thickness progression and risk of new plaque formation." These results suggested arterial injury in the carotid arteries — the two large vessels that supply blood to the head and neck.
"This may indicate that the association between long-term exposure to ozone and cardiovascular mortality that has been observed in some studies is due to arterial injury and acceleration of atherosclerosis," comments Wang.
However, the researchers admit that they're in the dark regarding what may cause this link. "We can show that there is an association between ozone exposure and this outcome, but the biological mechanism for this association is not well understood," Wang notes.
To the authors' knowledge, this is the first epidemiological study to examine the link between ozone exposure and "subclinical vascular disease" — that is, injuries that damage the artery walls before a heart attack or a stroke occurs.
According to the American Lung Association, ground-level ozone also damages lung tissue when we breathe it in. Frequently referred to as smog, ozone is a gas molecule that harms lung tissue by chemically reacting to it.