Tiny particles of pollutants emitted by automobiles, power plants and factories significantly increase the risk of dying from cardiovascular disease in the United States, according to a study led by Brigham Young University epidemiologist Arden Pope.
The research was published in "Circulation: Journal of the American Heart Association" on Dec. 15. Statistical links between air pollution and increased mortality were reported by Pope and others in the mid-1990s. In March of 2002 he and colleagues reported associations between air pollution and lung cancer, as well as the broad category of cardiopulmonary disease, which includes both heart and lung ailments.
The new study narrows the latter finding by identifying a strong link between particulate air pollution and ischemic heart disease (the type that causes heart attacks), and also a link between pollution and the combined category of irregular heart rhythms, heart failure and cardiac arrest. It also suggests general biological pathways through which pollution might cause these diseases that lead to death – increased inflammation and nervous system aberrations that change heart rhythm.
"Not only do we show a statistical link between particulate air pollution and these types of heart disease," Pope said, "but we see specific patterns that are consistent with mechanistic pathways that may help explain how air pollution causes those diseases. The study discusses recent advancements in cardiovascular medicine that have explored the role of inflammation in the development and progression of atherosclerosis. The study results are consistent with recent findings that air pollution may provoke low-grade pulmonary inflammation, accelerate the progression of atherosclerosis, and alter cardiac function. These results add biological plausibility that air pollution really is a risk factor for heart disease."
This study linked health statistics and levels of air pollution in scores of cities across the United States. The researchers used data from the American Cancer Society who tracked 500,000 individuals between 1982 and 1998. Data on date of death and cause of death were collected as were data on body mass, smoking habits, occupational exposures, diet and other individual risk factors. Then the scientists fed the mountains of data into complex statistical models that estimated the effects of air pollution while controlling for these other risk factors of cardiovascular disease.
The pollutant linked to cardiovascular deaths was particulate matter smaller than 2.5 microns, or PM2.5. Particulate matter is generated by combustion, most commonly by automobiles, manufacturing and coal-fired power plants.
The EPA has declared that the annual average level of PM2.5 particles in the air should not exceed 15 micrograms per cubic meter. Pope's study showed that each 10 micrograms-per-cubic-meter increase in fine particulate air pollution is accompanied by an 18-percent increase in risk of death from ischemic heart disease and a 13-percent increase in risk of death from altered heart rhythm, heart failure or cardiac arrest.
Further analysis also showed higher risks associated with air pollution for former and current smokers – 26 percent and 94 percent, respectively. Pope notes that "smoking is clearly a much larger risk factor, but air pollution increases the risk of cardiovascular death in non-smokers and seems to add additional risk to smokers."
"All of these findings illustrate the specific disease processes resulting from particulate air pollution and smoking both independently and together, and help investigators understand both the local and systemic responses of the human body when various types of particles are inhaled into our lungs," said John J. Godleski, M.D., a professor of pathology at Harvard Medical School and a co-author on the study. "The fact that significant associations were found with (specific types of) cardiac diseases. . . is an exciting advance in this field."
Pope emphasized that the study's findings are "good news." Since the early 1980s, the annual U.S. average of PM2.5 has dropped from 21 to 14 micrograms per cubic meter.
"The risk factor we have identified -- fine particulate air pollution -- is controllable," he said. "If we can further reduce our exposure to this pollutant we may reduce the number of deaths attributed to heart disease."
The study's other co-authors are: Richard Burnett and Daniel Krewski of the University of Ottawa; George Thurston of the New York University School of Medicine; Michael Thun and Eugenia Calle of the American Cancer Society; and Kazuhiko Ito of the NYU School of Medicine.
The research was supported by a grant from the National Institute of Environmental Health Sciences and a Health Effects Institute contract.