Heart attacks can be triggered by air pollution, more so than cocaine, scientists have found.
Heart attacks can also come on through alcohol consumption, coffee consumption and physical exertion.
Sex, anger, marijuana use and chest or respiratory infections, were not ruled out by scientists, either.
Air pollution, though, is by far the main culprit, particularly in areas of heavy traffic.
The findings, published in The Lancet journal, suggest widespread 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.
Air pollution is a “a major environmental risk to health”, according to the World Health Organisation (WHO), which estimates that it causes around 2 million premature deaths worldwide every year.
Nawrot’s team combined data from 36 separate heart attack studies and calculated the proportion of those estimated to have been caused by each trigger.
The highest risk population-attributable fraction (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 was no longer present.”
Air pollution in many major cities in Asia exceeds the WHO’s air quality guidelines. Toxic cocktails of pollutants in such countries results in more than 530,000 premature deaths a year.
Nawrot said the effects of passive-smoking were likely to be similar to that of outdoor air pollution, too.
He noted previous research, which found that bans on smoking in public places have significantly reduced heart attack rates.
British researchers have said that a smoking ban has slashed the incidence of heart attacks, saving the health service £8.4 million pounds in the first year.
It has been long established that not smoking, exercising, eating a healthy diet and maintaining their ideal weight can keep a heart attack at bay.