Traffic fumes can raise risk for heart attack for at least six hours: Study

By Dr. Ananya Mandal, MDSep 22 2011

According to British researchers breathing in heavy traffic fumes can trigger a heart attack. Heart attack risk is raised for about six hours post-exposure and goes down again after that, researchers found. They say in the British Medical Journal that pollution probably hastens rather than directly cause attacks. But repeated exposure is still bad for health, they say, substantially shortening life expectancy, and so the advice to people remains the same - avoid as far as is possible.

Prof Jeremy Pearson, associate medical director at the British Heart Foundation, which co-funded the study, said, “This large-scale study shows conclusively that your risk of having a heart attack goes up temporarily, for around six hours, after breathing in higher levels of vehicle exhaust. We know that pollution can have a major effect on your heart health, possibly because it can 'thicken' the blood to make it more likely to clot, putting you at higher risk of a heart attack. Our advice to patients remains the same - if you've been diagnosed with heart disease, try to avoid spending long periods outside in areas where there are likely to be high traffic pollution levels, such as on or near busy roads.”

Krishnan Bhaskaran and six colleagues at the London School of Hygiene and Tropical Medicine examined 79,288 heart attacks that occurred in 15 urban areas of England and Wales in 2003-06, from the Myocardial Ischemia National Audit Project. They then examined how much pollution occurred in those areas at the time those patients suffered their heart attack, using data from UK National Air Quality Archive. This enabled the investigators to plot hourly levels of air pollution (PM10, ozone, CO, NO2, and SO2) against onset of heart attack symptoms and see if there was any link. Higher levels of air pollution did appear to be linked with onset of a heart attack lasting for six hours after exposure. After this time frame, risk went back down again.

Krishnan Bhaskaran, who led the research, said the findings suggested that pollution was not a major contributing factor to heart attacks. For example, being exposed to a spell of medium-level rather than low-level pollution would raise heart attack risk by 5%, by his calculations. “If anything, it looks like it brings heart attack forward by a few hours. These are cardiac events that probably would have happened anyway.” But he said the findings should not detract from the fact that chronic exposure to air pollution was hazardous to health.

“We estimated that higher ambient levels of the traffic-associated pollutants, PM₁₀ and NO₂, were followed by a transiently increased risk of myocardial infarction up to six hours later,” the authors write. Prof Pearson from the BHF agrees, “Unhealthy diets and smoking etc are much bigger heart attack risk factors, but car fumes are the cream on the cake that can tip you over.”

Pollution is estimated to cause 29,000 premature deaths a year in the UK, including 4,200 in London alone, said Jenny Bates, an air pollution campaigner at Friends of the Earth. “This study adds to the urgent need for bold action to cut air pollution in order to comply with EU limits…It's outrageous that we're continuing to breathe this dirty air and that ministers haven't done enough to clean up our air,” she said.

A Department for Environment, Food and Rural Affairs spokesman said, “We want to keep improving air quality and reduce the impact it can have on human health and the environment. Our air quality has improved significantly in recent decades and almost all of the UK meets EU air quality limits for all pollutants…There are some limited areas where air pollution remains an issue but that's being dealt with by the air quality plans, which set out all the important work being done at national, regional and local levels to make sure we meet EU limits as soon as we can.”

Commenting on the study, Dr. Bertram Pitt, a professor of medicine emeritus at the University of Michigan School of Medicine in Ann Arbor, described the findings as “unsurprising,” but “credible.” “There's lots of data that shows that air pollution is a tremendous cardiac risk…So if you are part of a vulnerable population and you go out into traffic or something like that and it takes you beyond your threshold you might very well have a heart attack. And once you do, the damage that ensues can go on forever…So, the answer is of course to decrease air pollution. Which is, of course, nothing that we haven't heard before. But this is one more indication telling us to do whatever we can do to reduce air pollution exposure,” Pitt said.