Air pollution triggers (引发)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. Anger, marijuana (大麻)use and chest or respiratory (与呼吸有关的)     1     can also trigger heart attacks to different extents, the researchers said, but air pollution,       2     in heavy traffic, is the major cause.

The findings, published in The Lancet journal, suggest population-wide       3     like polluted air should be taken more       4     when looking at heart risks, and should be put into context besides 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.

Nawrot’s team combined data from thirty-six       5     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. “Of the triggers for 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       6     to it,” the researchers wrote. “PAFs give a measure of how much disease would be avoided if the risk was no longer       7    . ”

A report published late last year found that air pollution in many major cities in Asia exceeds the WHO’s air quality guidelines and that poisonous       8     of pollutants result in more than 530,000 earlier deaths a year. While       9     smoking was not included in this study, Nawrot said the effects of secondhand smoke were likely to be similar to that of outdoor air pollution, and noted previous research found that bans on smoking in public places have       10     reduced heart attack rates.