© CORBISTraffic fumes: more deadly than cocaine?
If a person with heart disease is exposed to heavy traffic fumes, their chance of having one increases by five per cent.
But because most people are exposed to traffic fumes, and only a small number take cocaine, on a population-wide basis traffic pollution triggers more heart attacks, concluded the Belgian researchers.
Applied to Britain, where there are around 124,000 heart attacks each year, traffic fumes could trigger 9,200 heart attacks, and cocaine around 1,100.
Scientists at Hasselt University and the Catholic University of Leuven, both in Belgium, came to their conclusions after looking at 36 studies.
These looked at heart attack risk factors in people with heart disease, such as taking physical exertion, having sex, eating a large meal, drinking alcohol or coffee, smoking marijuana and snorting cocaine.
These studies looked at how much taking part in such activity raised the risk of heart attack in an individual.
Dr Tim Nawrot, of the Centre for Environmental Sciences at Hasselt University, and colleagues then examined how many people were exposed to each type of risk.
By combining the two, they arrived at figures for what they called the "population attributable fraction". They described this as "a measure of how much disease could be avoided if the risk was no longer present".
They calculated that cocaine was therefore responsible for 0.9 per cent of heart attacks, and traffic fumes for 7.4 per cent.
Other important risks included physical exertion (6.3 per cent), drinking alcohol or coffee (5.0 per cent each), anger (3.1 per cent), eating a large meal (2.7 per cent) and sexual activity (2.2 per cent).
Writing in The Lancet, they concluded: "Our work shows that ever-present small risks might have considerable public health relevance.
"Improvement of the air we breathe is a very relevant target to reduce the incidence of this disease in the general population."
Previous studies have indicated that tiny specks from traffic fumes - called particulates - can worsen hardening of the arteries, a key sign of cardiovascular disease.
Commenting on the research, Dr Andrea Baccarelli, an environmental health expert at Harvard School of Public Health, and Dr Emelia Benjamin, from the Boston University School of Medicine, described the study as "an exemplary piece of epidemiological work that furthers our understanding of myocardial infarction triggers".
They added: "Their work stands as a warning against overlooking the public health relevance of risk factors with moderate or weak strength that have high frequency in the community."
Judy O'Sullivan, senior cardiac nurse at the British Heart Foundation, said: "It's important to remember this study looked at the triggers and not the causes of heart attacks."
She added: "However, given the large number of people living in the UK with heart disease and the likelihood of their exposure to air pollution, this study highlights how important it is that UK governments ensure they meet European Commission targets to improve air quality."
Prof David Spiegelhalter, Winton Professor Of The Public Understanding Of Risk at Cambridge University, had a more light-hearted take on the research.
"The suggestion that heart attacks could be reduced by 2 per cent if everyone stopped having sex is unlikely to be a popular public health message," he said.
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