By Brian Bienkowski
Environmental Health News
Nonsmoking women who live many years in communities polluted with fine particles have an elevated risk of lung cancer, according to new research.
The study, which is the largest to date to examine the link, adds to mounting evidence that chronic exposure to soot may raise the risk of lung cancer, particularly among nonsmokers.
"The results are dramatic in the sense that there appears to be a substantial effect of being close to air pollution in terms of risk for cancer," said Dr. Norman Edelman, a senior medical advisor with the American Lung Association who was not involved in the study.
Led by Harvard University researchers, the study estimated exposures of 103,650 U.S. women to three sizes of airborne particulates. They calculated how many women contracted cancer – 2,155 – between 1994 and 2010, and analyzed the pollution levels near their homes for the previous six years.
All sizes of particle pollution, particularly the smallest, or PM2.5, were linked to an increased risk of lung cancer. For every small (10-microgram per cubic meter) increase in PM2.5 the risk of lung cancer increased 37 percent among nonsmoking women or women who had quit smoking at least 10 years earlier, according to the study, which was published online in the journal Environmental Health Perspectives.
"Once you restrict to nonsmokers – people not getting bombarded with cigarette smoke – these associations do get much stronger," said senior author Francine Laden, a Harvard professor of environmental epidemiology.
The sources of the pollutants varied. Although the research suggested that traffic played a role in the higher cancer risk, the finding was not scientifically significant because too few women in the study lived near major roads.
Spewed by trucks, buses, cars, factories and fires, fine particles can penetrate deep into lungs, raising people's risks of respiratory problems and heart attacks.
More than 46 million Americans, or almost 15 percent, live in areas with unhealthful year-round levels of fine particle pollution, according to the American Lung Association. U.S. areas with the highest levels include the Los Angeles region, California's Central Valley, Chicago and Houston.
In the new study, about half of the women lived in the Northeast.
The research doesn't prove air pollution causes lung cancer. But it is the latest of multiple human health studies that have linked fine particles to lung cancer. Such studies prompted the International Agency for Research on Cancer to classify particulate matter as carcinogenic to humans last year.
Lung cancer is the leading cause of cancer death, killing about 160,000 Americans every year. Almost 90 percent of lung cancers are attributed to cigarette smoking, but an estimated 16,000 to 24,000 nonsmokers die of lung cancer every year in the United States, according to the American Cancer Society.
The researchers didn't have personal exposure for the women. Instead, they estimated their exposures by plugging local air quality data into models that took into account how close the women lived to major roads, as well as nearby industries and weather conditions.
Edelman of the American Lung Association said the study's strength was that it looked at a period of six years of exposure instead of a snapshot in time.
However, one researcher said the study didn't look far enough back in the women's past. Previous exposures may be more important because cancer can develop over a period of decades.
The study uses "more or less current exposure to categorize long-term response," said Fred Lipfert, an environmental engineer formerly of the Brookhaven National Laboratory who has published multiple articles on air pollution and health.
"The other problem I have? The words 'indoor air' don't appear anywhere," Lipfert said.
Indoor sources of particulates include cigarette smoke, cooking, wood-burners and kerosene heaters. The researchers don't know how often the women's windows were closed or how much time they spent outdoors, Laden said.
Laden agreed that past exposures are important, but the scientists were limited by the data. Particulates were not routinely measured a decade or two ago. "Ideally we would have exposure data for 20 years back," she said.
Nevertheless, it's "pretty certain that air pollution, specifically particulates, is a very important hazard," Laden said. "We're not sure that there's any safe level."