Air Pollution Linked to Cardiovascular Disease

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Air Pollution Linked to Heart Deaths

Risk May Be Higher Than Previous Studies Suggest By Salynn Boyles

WebMD Medical News Reviewed By Louise Chang, MD

on Wednesday, January 31, 2007

Jan. 31, 2007 -- Air pollution is a much bigger factor in death from

heart diseaseheart disease or strokestroke 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 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 menopausemenopause.

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.

'Overwhelming Evidence'

Environmental epidemiologist 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 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. "

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SOURCES: , K. The New England Journal of Medicine, Feb. 1,

2007; vol 356: pp 447-458. D. Kaufman, MD, MPH, professor of

environmental and occupational health sciences, epidemiology, and

medicine, University of Washington, Seattle. Luepker, MD,

cardiologist and professor of epidemiology, University of Minnesota;

spokesman, American Heart Association. W. Dockery, ScD,

professor of environmental epidemiology, Harvard School of Public

Health, Boston. " EPA Scientists Urge Tighter Smog Limits, "

Associated Press, Jan. 30, 2007. Environmental Protection Agency web

site: " Air Quality Data, " " EPA Air Quality Statistics by

City, " " Particulate Matter. "