A recent German study has found that 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. The researchers put most of the blame on polluted air.

The study was funded partly by the U.S. Environmental Protection Agency and appeared in the Thursday edition of The New England Journal of Medicine. The authors estimate that 8 percent of the heart attacks they studied were attributable to traffic. The triggers for a heart attack, which is a sudden event, are rarely understood, but, if the findings are confirmed, traffic will be added to the list of known list of triggers, which include outbursts of anger, strenuous exercise and use of cocaine.

'Given our current knowledge, it is impossible to determine the relative contribution of risk factors such as stress and traffic-related air pollution,' said the research team, led by Annette Peters of the National Research Centre for Environment and Health in Neuherberg.

Nonetheless, because air pollution is known to increase the probability of a heart attack, they said, people already at risk for heart problems 'are likely to profit from recent efforts to improve the air quality in urban areas with the use of cleaner vehicles and improved city planning.'

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. Traffic jams were more likely to take a toll on women and on people 60 and older.

The study
The Neuherberg findings were based on interviews with 691 volunteers based around Augsburg, a German city of about 260,000.

The patients were asked to outline their activities during the four days before their attacks which occurred between 1999 and 2001. The study discounted for the effect of hard exercise -- as when bicycling -- and for typical morning stress linked to heart attacks. The researchers found that one hour before the attack happened, exposure to traffic was twice as frequent as at any other time.

Traffic posed a risk regardless of the mode of transportation, with one in 12 heart attacks being linked to this source. Heart attacks were 2.6 times more common for people stuck in cars, 3.1 times higher for people stalled in traffic while taking public transportation, and 3.9 times greater for those jammed up while on a bicycle.

'We didn't expect it to be that strong,' said Peters. 'There are two things that are surprising: that the effect is so immediate -- you see it in one hour -- and then also the size.'

'Because the association was also observed for persons who used public transportation, it is unlikely that the effect is entirely attributable to the stress linked with driving a car,' the Peters team said.

However, researchers say it is 'unlikely that the effect is entirely attributable to the stress linked with driving a car' because people who traveled by public transport, including buses or trolley cars were equally affected.

Pollution as a Major Factor
Germany's roadways generally do not have speed limits but traffic can often grind to a halt after an accident or during vacation times, and traffic jams can leave motorists stranded for hours.

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.

Conclusively, pollution is likely to be the key factor. Elements in the air expelled by vehicle exhausts have been shown to increase the stickiness of the blood when breathed in, which can lead to blood clots forming, as well as altering the function of the heart and blood vessels, perhaps even moreso than in the lungs.

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.

'These changes have been observed in healthy officers of the highway patrol in association with the concentration of particulate matter in their vehicles and might be consistent with an increased risk of myocardial infarction [heart attack] after a transient elevation in the concentration of ambient particles in vulnerable subjects,' the authors write.

Additionally, air pollution is known to be a factor in heart disease, which develops slowly over decades, and research has shown that people living close to a main road have twice the risk of dying from the condition.

If these results are true, the study may have, in fact, revealed a preventable cause of cardiovascular disease.