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Air Pollution Linked to Heart Attacks

Risk raised even for short-term exposure

MONDAY, June 11, 2001 (HealthDayNews) -- If you're at risk for a heart attack, the coming summer months may further raise your odds: A new study finds that even brief exposure to air pollution can almost immediately increase the risk.

The study adds to the evidence linking heart attack risk to pollutants, specifically to fine particles from automobile exhausts, power plants, refineries and other sources.

The particles, designated PM2.5 because they are less than 2.5 microns in diameter (a micron is one millionth of a meter), are small enough to get through the normal defense mechanisms of the lung. Studies indicate they can then cause inflammation, thicken blood so that it flows less freely and stimulate formation of artery-clogging blood clots.

Recent studies have linked the incidence of heart attacks to day-to-day changes in particulate pollution, says Dr. Murray A. Mittleman, director of cardiovascular epidemiology at Beth Israel Deaconess Medical Center in Boston and lead author of a report in the June 12 issue of Circulation: Journal of the American Heart Association. The new study correlated hourly levels of air pollution with the occurrence of heart attacks in Boston.

"We started with patients who had heart attacks and survived," Mittleman says. "We interviewed them in hospitals to get precise information about when their symptoms began. Then we looked at the air pollution levels in the hours preceding the heart attacks and compared them with air pollution levels at other times."

Interviews with 772 heart attack patients confirmed previous findings linking heart attack risk to 24-hour average pollution levels, Mittleman says. Many were high-risk patients; one-third had already had a heart attack; nearly one-fifth were diabetic; 32 percent were smokers; 41 percent had high blood pressure, and 34 percent were obese.

"Because we were able to get fine data on timing, we were able to answer a question about whether there is a quick, short-time effect of particulate pollution. "We found that the effect occurred as little as two hours after an increase in air pollution," he says.

The report is timely because fine-particle pollution is highest on hot, hazy days in summer, the researchers say. And particulate pollutants can be blown far from their sources into regions away from major cities.

The U.S. Environmental Protection Agency's (EPA) current acceptable standard is 65 micrograms of PM2.5 per cubic meter of air. However, the Boston data shows a 48 percent higher risk for heart attack when the PM2.5 concentration rose by 25 micrograms per cubic centimeter.

Nevertheless, "the EPA standard is reasonable and should be enforced," Mittleman says. "EPA regulates 24-hour particulate levels. At this point, it is premature to consider whether shorter-term regulations are needed."

The finding has a political dimension since the energy plan proposed by Vice President Dick Cheney says environmental restrictions might be eased to avoid an energy shortage, Mittleman says.

"Based on these data, lowering the standards probably is not in the best interests of reducing heart disease," Mittleman says.

Other studies to confirm and expand the new findings are under way, says Dan Greenbaum, president of the Health Effects Institute, a nonprofit organization in Boston that helped fund the Mittleman work and is itself funded by the EPA and by private industry.

A study is underway in Germany to confirm the Boston findings, he says. Several other trials are attempting to single out the specific kinds of particles that affect the heart and lungs. In those studies, healthy volunteers will breathe air containing carefully measured amounts of pollutants.

"Are all particles equal in their effect on the cardiorespiratory system?" Greenbaum says. "It is important that we answer that question so that we can target our pollution reduction efforts."

What To Do

"People at risk of heart attacks should limit their outdoor activities on hot, hazy days when particulate levels are high, particularly if a warning is issued on high levels of particulates," says Mittleman. "They should stay indoors, preferably in an air-conditioned environment."

For research on air pollution and heart disease, go to the Health Effects Institute. You can also try the EPA.

Read other HealthDay articles about pollution.

SOURCES: Interviews with Murray A. Mittleman, M.D., Dr.Ph., director of cardiovascular epidemiology, Beth Israel Deaconess Medical Center, Boston, and Dan Greenbaum, president, Health Effects Institute, Boston; June 12, 2001 Circulation: Journal of the American Heart Association
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