Air pollution is a serious cardiovascular risk.

Exposure to air pollution contributes to the development of cardiovascular diseases, according to a new American Heart Association scientific statement. The statement was published in the June 1 print issue of Circulation: Journal of the American Heart Association.

"The increase in relative risk for heart disease due to air pollution for an individual is small compared with the impact of established cardiovascular risk factors such as high blood pressure or high cholesterol. Nevertheless, this is a serious public health problem because of the enormous number of people affected and because exposure to air pollution occurs over an entire lifetime," said Robert D. Brook, M.D., lead author of the statement and an assistant professor of medicine in the Division of Cardiovascular Medicine at the University of Michigan in Ann Arbor.

Previously, the American Heart Association had not drawn firm conclusions about the long-term effects of chronic exposure to different pollutants on heart disease and stroke because of flaws in the research design and methodology of many pollution studies.

For the new scientific statement, the association's experts conducted a comprehensive review of the literature on air pollution and cardiovascular disease. The statement focuses on particulate-matter pollution and reaffirms the dangers of environmental tobacco smoke--called secondhand smoke--as an air pollutant. Particulate matter (PM), also known as particle pollution, is composed of solid and liquid particles within the air.

The statement referenced several significant studies.

"A recent report from the American Cancer Society study cohort found that long-term exposure to fine-particulate air pollution at levels that occur in North America increased the risk for cardiovascular mortality. The risk increased by 12 percent for every increase of 10 micrograms per cubic meter of air ([micro]g/[m.sup.3]) in fine-particle concentration," Brook said.

He said that long term, levels of fine-particulate matter can vary among North American cities by as much as 30-40 [micro]g/[m.sup.3].

"The largest portion of this increased mortality rate was accounted for by ischemic heart diseases (i.e., coronary attacks): however, other causes also were increased, such as heart failure and fatal arrhythmias," he said.

The statement cited another study that suggested a person's exposure to the harmful components of air pollution may vary as much within a single city as across different cities. After studying 5,000 adults for eight years, the researchers of that study also found that exposure to traffic-related air pollutants was more highly related to mortality than were citywide background levels. For example, those who lived near a major road were more likely to die of a cardiovascular event.

The panel drew several conclusions about pollution:

* Prolonged exposure to elevated levels of particle pollution is a factor in reducing overall life expectancy by a few years.

* Short-term exposure to elevated levels of particle pollution is associated with the increased risk of death due to a cardiovascular event.

* Hospital admissions for several cardiovascular and pulmonary diseases are increased in response to higher concentrations of particle pollution.

The panel recommends that people with heart disease, cardiovascular risk factors, diabetes, or pulmonary disease limit outdoor activities when pollution is high, in accordance with U.S. Environmental Protection Agency (U.S. EPA) Air Quality Index recommendations.

During the last decade, epidemiological studies conducted worldwide have shown that elderly patients, people with underlying heart or lung disease, populations of lower socioeconomic status, and people with diabetes may be at particularly increased risk of incurring cardiovascular disease from air pollution.

All Americans should be aware of the potentially hazardous cardiovascular health effects of air pollution, according to the scientific statement. U.S. EPA provides daily information about ozone and particulate-matter levels for more than 150 cities at www.epa.gov/airnow.

"Health care providers and at-risk patients should be educated about the health risks related to air pollution and about the availability of daily air pollution updates," Brook said.

Air pollution is composed of many environmental factors, such as carbon monoxide, nitrates, sulfur dioxide, ozone, lead, secondhand tobacco smoke, and particulate matter. Particulate matter can be generated from vehicle emissions, tire fragmentation and road dust, power generation and industrial combustion, smelting and other metal processing, construction and demolition activities, residential wood burning, windblown soil, pollens, molds, forest fires, volcanic emissions, and sea spray.

Secondhand smoke is the single largest contributor to indoor air pollution when a smoker is present, according to the statement. Studies of secondhand smoke indicate that air pollution in general can affect the heart and circulatory system. Previous research has established that exposure to the secondhand smoke of just one cigarette per day accelerates the progression of atherosclerosis (hardening of the arteries), so the panel finds it plausible that even low doses of air pollution could have negative effects on coronary functions.

The statement noted that more research is needed to determine the underlying biological mechanisms and pathophysiological pathways that may contribute to the development of cardiovascular disease and to identify the toxicities of various air pollutants. The statement detailed several areas for future research.