The health risks associated with air pollution may be nearly three times greater than previously thought, according to a new report.

Researchers say earlier studies may have seriously underestimated air pollution’s health risks by basing their calculations on one or two air pollution measures from several cities and then comparing the health effects.

In the study, researchers took air pollution measurements at 23 sites within more than 260 neighborhoods in Los Angeles and then compared the risk of death and disease among 22,906 residents by ZIP code over two decades.

The results of this in-depth analysis show that the risk of death from any cause rose by 11 percent to 17 percent for each increase in the level of fine particles found in vehicle exhaust, smoke, and industrial emissions in the neighborhood’s air.

"By looking at the effects of pollution within communities, not only did we observe pollution's influence on overall mortality, but we saw specific links between particulate matter and death from ischemic heart disease, such as heart attack, as well as lung cancers," says researcher Michael Jarrett, PhD, associate professor of preventive medicine at the University of Southern California, in a news release.

Air Pollution Raises Risk of Death

Researchers say the fine particles less than 2.5 micrometers in diameter that are released into the air by the burning of fossil fuels -- such as gasoline, wood, and coal -- pose the greatest health risk because they can penetrate deep into the lungs and sometimes enter the bloodstream and lead to heart attack or stroke.

The results, published in the journal Epidemiology, showed that for each increase of 10 micrograms per cubic meter of fine particles in the neighborhood’s air, the overall risk of death rose 11 percent to 17 percent; heart-disease-related deaths rose by 25 percent to 39 percent.

In addition, the risk of death from diabetes was more than two times higher in areas of high air pollution, although the numbers of diabetes-related deaths was less reliable due to their smaller numbers.

"People who are diabetic may be more susceptible to day-to-day fluctuations in air pollution," says Jerrett. "They may experience a state of greater inflammation related to insulin resistance that makes their lungs more receptive to receiving harmful particles."

Previous Studies May Have Underestimated Risk

The study also showed that the level of fine particles in the air varied by about 20 micrograms per cubic meter from the cleanest parts of Los Angeles to the most polluted.

Researchers say these results suggest that a large air pollution study by the American Cancer Society that included more than a million people in 150 cities may have underestimated the health risks caused by air pollution by using average citywide air pollution levels rather than neighborhood-specific levels.

Health officials and policymakers have relied on findings from that study to set the nation’s air quality standards.

Researchers say the type of air pollution found in Los Angeles is strongly influenced by vehicle exhaust and more research is needed to determine if this type of air pollution is more dangerous than the type of air pollution found in the Eastern U.S., where power plants and factories contribute more heavily to air pollution.

By Jennifer Warner, reviewed by Louise Chang, MD

SOURCES: Jerrett, M. Epidemiology, November 2005; vol 16. News release, University of Southern California.