Air Pollution's Impact on the Heart Is as Bad as Having Been a Smoker

Air pollution's impact on the heart is as bad as having been a smoker(Embargoed for release 4 p.m. EST, Monday, December 15, 2003)

In a follow-up analysis of the most extensive study of its kind on the long-term effects of air pollution on human health, researchers have found that people living in U.S. cities face an increased risk of dying from a heart attack as a result of long-term exposure to air pollution. This increased risk was found to be as large as that associated with being a former smoker. The new analysis is published as a study in the rapid access issue of the journal Circulation, published by the American Heart Association.

"It is clear that long-term exposure to the levels of air pollution that Americans are routinely exposed to is a significant contributor to ischemic heart disease," says George Thurston, Sc.D., Associate Professor of Environmental Medicine at NYU School of Medicine, and one of the new study's authors. "When we looked at the data, we observed that the increased risk of dying from some forms of heart disease among non-smokers living in polluted cities is roughly comparable to the increased risk caused by being a former smoker."

The new analysis is based on data collected by the American Cancer Society (ACS) on the cause of death of some 500,000 adults over a 16-year period from 1982 to 1998 and on data on pollution levels in cities nationwide. These data sets were also the basis for an earlier study, published in the Journal of the American Medical Association (JAMA) in 2002. The JAMA study showed that over many years, the danger of breathing soot-filled air in American cities significantly raised the risk of dying from lung cancer and heart disease, and the risk was comparable to the health risks of living with a smoker.

The new analysis by researchers George Thurston of New York University School of Medicine, and Arden Pope of Brigham Young University in Provo, Utah, (both Drs. Thurston and Pope were authors of the JAMA study), and by colleagues from other institutions, further categorized the cause of death in the group of 500,000 adults. They identified death from ischemic heart disease (i.e., heart failure resulting from decreased oxygen supply to the heart muscle), and death from other forms of heart disease, such as hypertension, and aortic aneurysms (bulges in the aorta). They also looked at diseases of the respiratory system that were listed as the primary cause of death on death certificates.

They found that long-term exposure to tiny particles of soot and dust, or PM2.5, was linked to a 31 percent increase in the risk of dying from ischemic heart disease, including fatal myocardial infarctions. This risk is comparable to the increased risk of dying of ischemic heart disease found by this study to be associated with being a former smoker (33 percent). The researchers based this calculation on an average mean of 17.1 micrograms of fine particulate matter (PM2.5) per cubic meter in the air of 51 metropolitan areas in the study across the nation. These metro areas include some 319,000 individuals who were part of the earlier study. They used this group because pollution data were available for these cities at both the start and end of the study, allowing the best characterization of long-term PM2.5 exposure in these cities.

Previous studies have linked chronic exposure to small particles in the air to death from heart disease and lung cancer. However, these earlier studies did not include such a large and well-characterized cohort of participants as the ACS cohort does. Consequently, the previous studies could not meaningfully investigate these sub-categories of mortality, such as ischemic heart disease, in order to evaluate the underlying mechanisms of causing deaths associated with air pollution. This study is the first to provide such insight into the origins of this association, and therefore the first also to allow detailed comparisons with other causes of cardiac death, such as smoking.

In addition to Drs. Thurston and Pope, the authors of the study are: Richard Burnett, Ph.D., an Daniel Krewski, Ph.D. of University of Ottawa; Michael Thun, and Eugenia Calle, Ph.D., of the American Cancer Society; and John Godleski, M.D., of Harvard Medical School.