Air pollution is a bigger trigger of heart attacks in the population than physical exertion, alcohol and taking cocaine, a study has shown.

On an individual basis, cocaine is a huge risk factor for having a heart attack, raising the risk 23 times. But since far more people are exposed to traffic fumes and factory emissions than cocaine, air quality is a far more important population-wide threat.

Scientists looked at “final straw” risk factors for triggering heart attacks, rather than underlying causes of heart disease.

Analysing evidence from 36 epidemiological studies, they calculated “population-attributable fractions” (PAFs), giving the proportion of total heart attacks caused by a different triggers.

The highest PAF of 7.4 per cent was attributed to traffic exposure, followed by physical exertion (6.2 per cent), alcohol (five per cent), coffee (five per cent), and higher levels of small air pollutant particles known as PM10s (4.8 per cent). Other risk factors included negative emotions, with a PAF of 3.9 per cent, anger (3.1 per cent), eating a heavy meal (2.7 per cent), positive emotions (2.4 per cent) and sexual activity (2.2 per cent). Overall, air pollution triggered between five per cent and seven per cent of heart attacks in the population.

Although cocaine raised a person’s risk of having a heart attack 23 times, it accounted for just 0.9 per cent of all heart attacks. The researchers, led by Tim Nawrot, from Hasselt University in Diepenbeek, Belgium, wrote in The Lancet medical journal online: “Of the triggers for myocardial infarction (heart attack) studied, cocaine is the most likely to trigger an event in an individual, but traffic has the greatest population effect as more people are exposed to the trigger.