Air pollution triggers more heart attacks than using cocaine and poses as high a risk of sparking a heart attack as alcohol, coffee and physical exertion, scientists said on Thursday.

Sex, anger, marijuana use and chest or respiratory infections and can also trigger heart attacks to different extents, the researchers said, but air pollution, particularly in heavy traffic, is the major culprit.

The findings, published in The Lancet journal, suggest population-wide factors like polluted air should be taken more seriously when looking at heart risks, and should be put into context beside higher but relatively rarer risks like drug use.

Tim Nawrot of Hasselt University in Belgium, who led the study, said he hoped his findings would also encourage doctors to think more often about population level risks.

“Physicians are always looking at individual patients — and low risk factors might not look important at an individual level, but if they are prevalent in the population then they have a greater public health relevance,” he said in a telephone interview.

The World Health Organization (WHO) describes air pollution as “a major environmental risk to health” and estimates that it causes around 2 million premature deaths worldwide every year.

Nawrot’s team combined data from 36 separate studies and calculated the relative risk posed by a series of heart attack triggers and their population-attributable fraction (PAF) — in other words the proportion of total heart attacks estimated to have been caused by each trigger.

The highest risk PAF was exposure to traffic, followed by physical exertion, alcohol, coffee, air pollution, and then things like anger, sex, cocaine use, smoking marijuana and respiratory infections.