Jan. 31, 2007 -- Air pollution is a much bigger factor in death from heart disease or stroke than has previously been recognized, according to findings from one of the largest studies ever to examine the issue.
Researchers followed close to 66,000 women -- aged 50-79 -- living in 36 cities. All the women were enrolled in the ongoing health study, the Women’s Health Initiative.
After adjusting for other risk factors for heart disease and stroke, they found that air quality was a strong predictor of heart disease and stroke risks -- and an even stronger predictor of death from heart disease or stroke.
Fine particulate air pollution -- caused primarily by vehicle exhausts, coal-fired power plants, and other industrial sources -- was the sole type of air pollution associated with increased risk.
When all other risk factors were equal, the researchers found that women living in the most polluted cities had the highest heart disease and stroke risks, while women living in the cleanest cities had the lowest.
A resident of Birmingham, Ala., one of the smoggiest cities included in the study, would have roughly a 76% increased risk of dying from cardiovascular causes than someone living in Tucson, Ariz., which was among the cities with the cleanest air.
Researcher Joel Kaufman, MD, MPH, of the University of Washington, tells WebMD that the findings highlight the importance of taking steps to reduce levels of fine particulate pollution in the air.
The study, funded in part by the Environmental Protection Agency (EPA), is published in the Feb. 1 issue of The New England Journal of Medicine.
“We have to think seriously about pollution exposures,” Kaufman says. “Pollution is not just a nuisance, it affects human health. We should be working to reduce exposures in whatever ways we can.”
More Exposure, Greater Risk
The study included only postmenopausal women, and there is some suggestion that this group is particularly vulnerable to the effects of air pollution. That is because a woman’s heart disease and stroke risks rise dramatically with menopause.
But there is little reason to believe that heart disease and stroke risks associated with exposure to dirty air are dramatically different for women and men, Kaufman says.
A total of 65,893 women without a history of heart disease or stroke were followed for an average of six years. During this time, 1,816 of the women experienced fatal or nonfatal cardiovascular events.
EPA air quality data were examined to determine each woman’s level of exposure to air pollutants, depending on where she lived.
Fine particulate air pollution is measured in micrograms per cubic meter. According to the EPA, fine particles of 2.5 micrometers or smaller are in smoke and haze. They can occur because of gases from industrial plants and cars.
The 36 cities represented in the study had average levels of this type of pollution ranging from 3.4 micrograms per cubic meter (in Honolulu) to 28.3 (in Riverside, Calif.), write the researchers.
According to the EPA, in 2005, Los Angeles, Birmingham, Detroit, and Pittsburgh were among the cities with the most fine particulate air pollution, with pollution levels ranging from 18 to 21 micrograms per cubic meter.
Tucson, Ariz.; Miami; and Reno, Nev., were among the cities with the cleanest air, with levels below 10.
After adjusting for other heart disease and stroke risk factors, Kaufman and colleagues concluded that each 10-unit increase in air levels of fine particulate matter was associated with a 76% increase in the risk of death from cardiovascular disease.
Higher long-term exposure to air pollution was also linked to an increased risk for developing cardiovascular disease.
Environmental epidemiologist Douglas Dockery, ScD, of the Harvard School of Public Health, tells WebMD that it is now clear that fine particle air pollutants poses a unique risk to health, but the reason for this is not so clear.
“It may be their chemical composition, their size, or their ability to transport other pollutants deep into the lungs,” he says. “There is a lot of research going on right now attempting to figure this out.”
Dockery says the scientific evidence supporting tighter restrictions on fine particle pollution levels is now overwhelming.
EPA officials failed to tighten these restrictions when they considered the matter last fall, ignoring the recommendations of the agency’s own scientists.
On Wednesday, EPA scientists called for tightened restrictions on ozone pollution, according to the Associated Press, which quoted a government official as saying that the move was also likely to stir controversy within the agency.
“The [Washington University] findings provide important new information about the health risks associated with air pollution that needs to be addressed,” Dockery says.
American Heart Association spokesman Russell Luepker, MD, MS, agrees that federal regulators could be doing much more to address the problem.
Luepker is a cardiologist and a professor of epidemiology at the University of Minnesota.
“We have the technology to reduce the fine particle pollutants in the air, but we don’t have the political will,” he says. “As with many environmental issues, we have seen a great deal of resistance to change.”