Does heavy traffic make you feel all sweaty and tight in the chest? It could be more than road rage: It could be a heart attack.
People prone to a heart attack face triple their usual risk as a result of traffic, whether they are in cars, on bicycles or on mass transit, according to a German study. The researchers put most of the blame on polluted air.
Studies have long tied respiratory disease to air pollution. More recent evidence over the past decade shows that microscopic particles in the air also hurt the heart and blood vessels, probably even more than the lungs.
"If these results are true _ and I think the evidence is pretty compelling _ then this is a preventable cause of cardiovascular disease," said pollution researcher Arden Pope of Brigham Young University.
The German study was funded partly by the U.S. Environmental Protection Agency. It was published Thursday in The New England Journal of Medicine.
The researchers interviewed 691 heart attack survivors around Augsburg, a German city of about 260,000. They were questioned about their activities on the four days leading up to their heart attack. The study discounted for the effect of hard exercise _ as when bicycling _ and for typical morning stress linked to heart attacks.
The study participants had traveled largely in Augsburg, but also on some small-town and rural roads.
In the end, they were three times more likely to suffer a heart attack within an hour of driving, riding or bicycling than they were during their activities away from traffic. That would make traffic to blame for 8 percent of their heart attacks.
"We didn't expect it to be that strong," said lead researcher Annette Peters, at the GSF National Research Center in Neuherberg, Germany. "There are two things that are surprising: that the effect is so immediate _ you see it in one hour _ and then also the size."
Previous studies have mostly suggested that pollutants cause gradual heart and circulatory damage over years of exposure. The invading particles may ratchet up the body's immune defenses, contributing to the blood vessel blockages of heart attacks.
However, the immediate risk seen in the German study may stem from the ability of tiny air contaminants to trigger a reflex that disturbs the heart's rhythm, researchers said.
Earlier studies have linked heart trouble to stress _ the kind that commuters encounter daily in traffic. The German researchers acknowledged that stress and noise might have contributed to the higher risk of a heart attack, but they saw the effect even in the quieter, more relaxing setting of a bus or train ride.
"The clever contribution of the Peters study was the exposure to traffic, not exposure to cars," said Dr. Peter Stone, a Harvard Medical School cardiologist who wrote an accompanying commentary. "The road-rage phenomenon, which might be related to cars, is probably much less of a feature in riding bicycles or buses."
Germany uses a lot of diesel fuel, and so its air pollution is somewhat different from that in the United States. EPA air pollution scientist John Bachmann said the risk might be different in magnitude in the United States but would still presumably be present.
The EPA has been working to reduce particle levels since the early 1970s. The smaller particles from manmade sources _ the size implicated in heart attacks _ dropped by 17 percent nationally between 1993 and 2002, according to agency data.
In recent years, cardiovascular risk has joined respiratory damage as a rationale for the regulations, Bachmann said.
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On the Net:
New England Journal of Medicine: http://nejm.org
EPA page on particulate pollution: http://www.epa.gov/airtrends/pm.html
