Numerous studies have shown associations of chronic exposure to airborne particles and increased health risks. Recent evidence on adverse effects of particulate air pollution on public health has motivated the development of more stringent standards for levels of particulate matter in outdoor air in the United States and in other countries, according to background information in the article. In 1997, the standard for airborne particulate matter was revised, maintaining the previous indicator of particulate matter of less than or equal to 10 μm in aerodynamic diameter (PM10) and creating a new indicator for fine particulate matter of less than or equal to 2.5 μm in aerodynamic diameter (PM2.5). Particles in this size range have a much greater probability of reaching the small airways and the alveoli (air sacs) of the lung than do larger particles. Evidence is limited on the health risks of this size range of particulate matter.
Francesca Dominici, Ph.D., of Johns Hopkins University, Baltimore, and colleagues conducted a study to estimate the risk for cardiac and respiratory diseases from exposure to fine particulate air pollution. The researchers analyzed data from a national database for 1999 through 2002 on hospital admission rates (constructed from the Medicare National Claims History Files) for cardiovascular and respiratory outcomes and injuries for 11.5 million Medicare enrollees (aged 65 years or older) who lived in 204 U.S. urban counties (population greater than 200,000). The individuals lived an average of 5.9 miles from a PM2.5 monitor.
The researchers found there was a short-term increase in hospital admission rates associated with exposure to PM2.5 for all of the health outcomes except injuries. The largest association was for heart failure, which had a 1.28 percent increase in risk per 10-μg/m3 increase in same-day PM2.5. Cardiovascular risks tended to be higher in counties located in the Eastern region of the United States, which included the Northeast, the Southeast, the Midwest, and the South.
"In the lung, particulate matter may promote inflammation and thereby exacerbate underlying lung disease and reduce the efficacy of lung-defense mechanisms. Cardiovascular effects may reflect neurogenic [arising in or stimulated by nerve tissues] and inflammatory processes," the authors write.
"Our findings indicate an ongoing threat to the health of the elderly population from airborne particles and provide a rationale for setting a PM2.5 National Ambient Air Quality Standard that is as protective of their health as possible," the researchers write. "The sources of particles contributing to the observed risks need to be identified so that control strategies can be targeted efficiently."
(JAMA. 2006;295:1127-1134. Available pre-embargo to the media at www.jamamedia.org)
Editor's Note: For funding/support information, please see the JAMA article.