Air pollution triggers more heart attacks than cocaine and poses as high a risk of acute myocardial infarction as alcohol, coffee and physical exertion say researchers.
Sex, anger, marijuana use and chest or respiratory infections can trigger myocardial infarctions to different extents, the researchers said, but air pollution, particularly in heavy traffic, is the major culprit.
The findings, published in the Lancet, 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.
Dr 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.
Environmental health risk
The World Health Organisation (WHO) describes air pollution as "a major environmental risk to health" and estimates that it causes around 2 million premature deaths worldwide every year.
Dr 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).
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.
"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 exposed to it," the researchers wrote. "PAFs give a measure of how much disease would be avoided if the risk were no longer present."
A report published in 2010 found that air pollution in many major cities in Asia exceeds the WHO's air quality guidelines and that toxic cocktails of pollutants results in more than 530,000 premature deaths a year.
While passive smoking was not included in this study, Dr Nawrot said the effects of second-hand smoke were likely to be similar to that of outdoor air pollution, and noted previous research which found that bans on smoking in public places have significantly reduced heart attack rates.
British researchers said last year that a ban on smoking in public places in England led to a swift and significant drop in the number of heart attacks, saving the health service 8.4 million pounds (about R94 million) in the first year.
A few days ago, New York City issued a ban on smoking in outdoor public places, the ban will take effect closer to the end of 2011.
Dr Tim Chico, a cardiologist at the University of Sheffield who wasn't involved in this research, said the findings would help health authorities focus on which triggers are the most important.
"However, what triggers the heart attack should be considered the "last straw." The foundations of heart disease that lead to a heart attack are laid down over many years, he said.
(Reuters Health, Kate Kelland, February 2011)