Traffic Pollution May Raise Short-Term Heart Attack Risk

Effect only lasts up to 6 hours, seems to affect mainly those already at risk, study suggests

WEDNESDAY, Sept. 21, 2011 (HealthDay News) -- Exposure to high levels of traffic-related air pollution appears to temporarily boost the risk for experiencing a heart attack, new British research suggests.

However, the apparent elevation in risk is short-lived, the study team noted, lasting for only one to six hours following exposure and dissipating entirely thereafter.

What's more, air pollution exposure may not bump up overall cardiac risk as much as fast-track it, increasing the chances that an individual already facing a probable heart attack threat will experience it slightly sooner than otherwise.

The finding, published in the Sept. 20 issue of the BMJ, is the work of a team led by Krishnan Bhaskaran, a lecturer in statistical epidemiology in the department of non-communicable diseases epidemiology at the London School of Hygiene and Tropical Medicine.

To assess the potential impact of air pollution on heart health, the investigators analyzed the cases of just over 79,000 patients in England and Wales who experienced a heart attack between 2003 and 2006 in one of 15 different relatively large (London) and small (Cardiff) urban settings.

After noting the hour of each patient's heart attack, the team analyzed relevant time-sensitive regional air pollution data regarding pollutant particles (PM10), carbon monoxide, sulfur dioxide, ozone and nitrogen dioxide levels that had been gleaned from the U.K. National Air Quality Archive.

Nitrogen dioxide and PM10, Bhaskaran and colleagues specifically noted, are primarily the product of motor vehicles in urban settings. As such, the team attributed elevations of each to be an indicator of exposure to traffic-related pollution.

After adjusting for various factors such as air temperature, humidity, general flu and viral conditions, holiday occurrences and specific days of the week, the team found that higher ambient levels of both PM10 and nitrogen dioxide did appear to be linked to a short-term rise in the risk of experiencing a heart attack.

But although they looked at heart attack risk for up to 72 hours following air pollution exposure, there appeared to be no increase in risk outside of the one- to six-hour range.

Despite that observation, the team noted in a journal news release that although there may be "limited potential for reducing the overall burden of myocardial infarction through reductions in pollution alone . . . that should not undermine calls for action on air pollution, which has well-established associations with broader health outcomes including overall, respiratory and cardiovascular mortality."

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," he noted. "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," Pitt explained.

"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.

More information

For more on pollution and heart disease, visit the U.S. National Institute of Environmental Health Sciences.

SOURCES: BMJ, news release, Sept. 20, 2011; Bertram Pitt, M.D., professor, medicine emeritus, University of Michigan School of Medicine, Ann Arbor
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