LOS ANGELES (Sept. 20)-Experts may be significantlyunderestimating air pollution's role in causing early death, accordingto a team of American and Canadian researchers, who studied twodecades' worth of data on residents of the Los Angeles metro area.
Whenthe epidemiologists examined links between particle pollution andmortality within more than 260 Los Angeles neighborhoods, they foundthat pollution's chronic health effects are two to three times greaterthan earlier believed. The study appears in the November issue ofEpidemiology but was published early on the journal's Web site.
Amongparticipants, for each increase of 10 micrograms per cubic meter(µg/m3) of fine particles in the neighborhood's air, the risk of deathfrom any cause rose by 11 to 17 percent, according to Michael Jerrett,Ph.D., associate professor of preventive medicine at the Keck School ofMedicine of the University of Southern California and the paper's leadauthor. Fine particle levels can differ by about 20 µg/m3 from thecleanest parts of Los Angeles to the most polluted.
"By lookingat the effects of pollution within communities, not only did we observepollution's influence on overall mortality, but we saw specific linksbetween particulate matter and death from ischemic heart disease, suchas heart attack, as well as lung cancers," Jerrett says. Ischemic heartdisease mortality risks rose by 25 to 39 percent for the 10µg/m3increase in air pollution.
Earlier studies took one or twopollution measures from several cities and compared health effectsamong cities. This study digs more deeply, taking pollution measures at23 sites within Los Angeles to more accurately reflect air pollutionexposure where residents live and work.
Researchers examined datafrom 22,906 residents of Los Angeles, Riverside, San Bernardino andVentura counties in the American Cancer Society's Cancer PreventionStudy II since 1982. They determined air pollution exposure in 267different zip codes where participants lived. The vast number ofparticipants allowed scientists to control for dozens of factors thatinfluence health outcome, such as smoking, diet and education. Finally,they compiled causes of death for the 5,856 participants who died by2000.
When considering air pollution, the epidemiologistsspecifically looked at levels of particulate matter, a mixture ofairborne microscopic solids and liquid droplets. That includes acids(such as nitrates), organic chemicals, metals, dust and allergens.
Smallparticles less than 2.5 micrometers in diameter pose the greatestproblems to health because they can penetrate deep into the lungs andsometimes even enter the bloodstream. In this study, the researcherstracked this particulate matter, called PM2.5 for short, across theneighborhoods of Los Angeles. It is often found in smoke, vehicleexhaust, industrial emissions and haze, driven by the burning of fossilfuels. Scientists also tracked ozone pollution, but found no linkbetween ozone levels and mortality.
Increased deaths from heartdisease jibe with the scientists' earlier research showing linksbetween air pollution and atherosclerosis, a thickening of artery wallsthat may lead to heart attack and stroke. They believe particulatematter may promote inflammatory processes, including atherosclerosis,in key tissues. "We have convincing evidence that those causes of deaththat we might expect from inflammation, ischemic heart disease and lungdisorders, are elevated in areas of higher pollution levels," he says.
Researchersalso saw more than a twofold increased risk of death from diabetes,although numbers of diabetes-related deaths were smaller than thosefrom heart disease, making findings less reliable. "People who arediabetic may be more susceptible to day-to-day fluctuations in airpollution," Jerrett says. "They may experience a state of greaterinflammation-related to insulin resistance-that makes their lungs morereceptive to receiving harmful particles."
Jerrett notes thatfindings might have been affected by participants who moved during thestudy or who changed their lifestyle since 1982. Another limitation isthat scientists could only use participants' zip codes, rather thantheir home addresses, to determine their home neighborhood.
Researcherswill conduct a similar study in New York City to try to duplicatefindings. They hope to determine whether Los Angeles'tailpipe-emission-driven pollution poses a greater danger than that inthe eastern United States, where power plants and factories contributemore heavily to pollution. They also plan to better understandpollution's effects on diabetes, and will use more specific measures toassess pollution within neighborhoods.
Because of the largenumber of participants in the American Cancer Society's study (morethan a million people in 150 cities), policymakers in the past haverelied heavily on findings from the study to set the nation'sair-quality standards.
"These findings should give us some pauseto think about what we need to do as a society," Jerrett says."Restrictions on tailpipe emissions have gotten tighter, but there aremore trucks and cars on the roads and people are driving farther. Thisstudy may cause us to reflect on how we use our cars, what cars wedrive and whether we can do anything to make tailpipe emissions fromall vehicles less harmful to health."
The Health Effects Institute and the National Institute of Environmental Health Sciences supported the research.
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