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Smog Linked to Heart Attacks

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WebMD Health News
Reviewed by Gary D. Vogin, MD

June 11, 2001 -- Those lazy, hazy days of summer can be hard on your heart, says a team of Harvard researchers.

The summer season usually comes with an increase in tailpipe and smokestack exhaust, and that type of air pollution can trigger heart attacks, says Murray A. Mittleman, MD, PhD, who reports the findings in Circulation, the Journal of the American Heart Association. Heart attacks can occur "within two hours of exposure to pollutants," he tells WebMD.

Earlier studies have linked heart attacks to exposure to pollution caused by relatively large particles, but Mittleman says his work shows that even microscopic particles less than 2.5 micrometers in diameter -- "a type of pollution associated with cars and industrial emissions," he says -- can be dangerous.

These toxins are breathed into the lungs, where their tiny size allows them to escape the lung's natural filtering system and enter the bloodstream. Mittleman says he doesn't know how these poisonous particles cause heart attacks but says they may make the blood thicker and stickier, which could lead to blood-clot formation and, ultimately, heart attacks.

Another theory, he says, is that the particles may actually damage the delicate lining of blood vessels.

The Environmental Protection Agency standards allow for a concentration of 65 mcg of these particles per cubic meter of air, but Mittleman says actual risk for heart attack starts at a much lower threshold -- only 25 mcg/m3. Breathing smoggy air that contains even this so-called safe level of pollutants can increase risk for heart attack by 48% during the period immediately following exposure, he says.

And it can do so quickly. Mittleman, assistant professor at Harvard Medical School and director of cardiovascular epidemiology at Beth Israel Deaconess Hospital, both in Boston, says he and his colleagues found that heart attacks can occur within two hours of breathing contaminated air.

As a result, "People with existing heart disease should stay indoors in a filtered environment on days when air pollution alerts are issued," Mittleman tells WebMD.

Mittleman's team arrived at its conclusion by interviewing 772 heart-attack patients treated between January 1995 and May 1996. Patients were asked about activities immediately before their heart attack. The researchers connected the onset of heart attack symptoms to daily pollution measurements collected during the study.

This paper is the "first to really provide a link between air pollution and the acute triggering of heart attacks," says Greg Burke, MD, MS, professor and chair of the department of public health sciences at Wake Forest University School of Medicine, in Winston-Salem, N.C.

"In my view this is a confirmation for what is being said when pollution warnings are issued: that those at high risk, especially the elderly and the very young, need to be careful," says Burke, a spokesperson for the American Heart Association who was not involved in the study.

"Being careful" probably means staying in an air-conditioned environment, Mittleman says, because "these very tiny particles can easily penetrate the interior, nonfiltered air in a home."

If one does have to venture outside on day when the air-quality index is in the unhealthy range, "then it is a good idea to avoid any type of exercise," he says. "We don't know if exercise can make the heart attack risk even greater, but it is logical to assume that taking in a bigger dose -- as is the case when one is breathing rapidly -- increases exposure and could increase risk."

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