The scientific evidence has not been strong enough until now to support such a position, said a scientific statement in the June 2 issue of the association journal Circulation. But recent studies clearly establish the risk, especially from the fine particles emitted by sources such as diesel engines, power plants and industrial activity, it said.

No single study was responsible, said Dr. Robert D. Brook, an assistant professor of medicine at the University of Michigan who headed the committee that drew up the statement, just "a sense among those responsible that the level of evidence had risen to "a point where for the first time, the American Heart Association [AHA] should recognize air pollution as a public health problem."

One study cited by the committee, done by the American Cancer Society, reported a numerical relationship between risk and exposure, with the risk of death from a cardiovascular event increasing by 12 percent for every increase of 10 micrograms per cubic meter of air of fine particle pollutants.

Levels of fine particulate pollution can vary by 30 milligrams or 40 milligrams per cubic meter of air day by day, Brook said.

Most of those deaths triggered by air pollution are due to heart attacks and other events that cause blockage of arteries, but deaths from other causes such as heart failure and heart rhythm abnormalities also rise as pollutant levels increase, Brook said.

"Prolonged exposure to elevated levels of particle pollution is a factor reducing overall life expectancy by a few years," the association statement said. "Short-term exposure to elevated levels of particle pollution is associated with the increased risk of death due to a cardiovascular event."

Tracking Daily Pollution Levels

Air pollution does not pose as great a risk as other established factors, such as high blood pressure and high cholesterol, Brook said, but health-care providers and people in general need to pay attention to it.

It's especially important for people at high risk — those older persons or those with diabetes, for example — to be aware of day-to-day levels of air pollution, Brook said. When pollution levels go up, they can take simple protective measures such as restricting activity or staying indoors in a less-polluted environment, he said.

"They should be aware of the Environmental Protection Agency Web site or media sources that make daily air pollution levels available daily," Brook said.

The warning about air pollution laps over to cover secondhand cigarette smoke, the major form of indoor air pollution, said Dr. Sidney C. Smith Jr., a professor of medicine at the University of North Carolina and an AHA spokesman. Cigarette smoke is rich in fine particles, Smith noted.

"Studies show that in people with otherwise normal coronary arteries, exposure to secondhand smoke can change the response of the arteries similar what is seen in smokers," he said.

The AHA will not get into the politically sensitive controversy about controls of power plant emissions, Brook said. But, he added, "We hope that these conclusions will provide further support to the importance of the present-day air quality standards."

More information

Daily pollution readings for more than 150 cities are provided by the U.S. Environmental Protection Agency.