Krishnan Bhaskaran, an epidemiologist at the London School of Hygiene and Tropical Medicine, and colleagues reviewed 79,288 heart attack cases from 2003 to 2006 -- noting exposure, by the hour, to pollution levels. The authors used the British National Air Quality Archive to investigate the levels of specific pollutants in the atmosphere including pollutant particles, carbon monoxide, nitrogen dioxide, sulphur dioxide and ozone.
Higher levels of pollutant particles and nitrogen dioxide are well-known markers of traffic related pollution, Bhaskaran said.
The study, published in the British Medical Journal, found high levels of pollution could increase the risk of having a heart attack for as long as 6 hours after exposure, but no increased risk after the 6-hour time frame.
Given the transient nature of the increased risk, the researchers speculated the heart attack would have happened anyway and was merely brought forward by a few hours.
This is known as a short-term displacement or "harvesting" effect of pollution, the researchers said.
"Limited potential for reducing the overall burden of myocardial infarction through reductions in pollution alone, but 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," Bhaskaran said.