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Researchers say people traveling in traffic are 3 times more likely to suffer a heart attack whether driving a car， riding a bus or bicycling. They say the risk of a heart attack is greatest within an hour of being in traffic.? Researchers believe the main reason is polluted air.

The findings are based on a study by the National Research Center for Environment and Health in Neuherberg， Germany. The study involved almost 700 people who suffered heart attacks. The patients described their? ? activities during the 4 days before their heart attack. Researchers found that those who had been in traffic were 3 times more likely to have a heart attack within one hour， compared to those who had not been in traffic.

Most of those in the study had been tra- veling by car. But some had been on bicycles and others were on buses. Women， people over the age of 60 and those already at risk for heart problems were most at risk.

Research shows that people in cars and buses are exposed to 10 times the amount of pollutants as people walking on the street. That is largely because they breathe in the particles and gasses released from the vehicles in front of them. Over time， these small particles speed the buildup of a sticky substance in the blood. This can cause blockages to form in the arteries① around the heart and lead to a heart attack.

Earlier studies have linked traffic， air pollution and heart disease. They found that people who live near major roads are at greater risk of dying from heart and lung problems. Other studies have also linked heart trouble to stress， similar to the kind that people face while driving in heavy traffic. But the researchers of the latest study say they do not know whether the increased heart attack risk was the result of stress or pollution. They suggest it may be a combination of stress， noise and pollution.

The study found that traffic was linked to 8% of heart attacks. But experts note that the overall risk of having a heart attack after being in traffic is still very low.

Annette Peters， who led the research， said the research shows the need for cleaner vehicles and better city planning.

注：① arteries 動脈