Exposure to high levels of traffic pollution may boost your risk of heart attack, according to a new study published on BMJ.com.
But the study found that the risk was transient, lasting one to six hours, and that rather than increasing overall risk of heart attack, exposure to pollution appeared to precipitate cardiac events in people who were already at higher-than-average risk.
Researchers in epidemiology at the London School of Hygiene and Tropical Medicine analyzed data on 79,288 patients who had a heart attack between 2003 and 2006 in 15 urban areas of England and Wales. To determine patients’ exposure to ambient air pollution, the team compared the recorded hour of each heart attack with regional air pollution information from the U.K. National Air Quality Archive. That data offered information about pollutant particles, ozone, carbon monoxide, sulfur dioxide and nitrogen dioxide levels.
After controlling for environmental factors like air temperature, humidity and viral infection rates, along with social factors like holidays and day of the week, the researchers found that exposure to high levels of certain components of air pollution — pollutant particles and nitrogen dioxide, which are a byproduct of car traffic — was associated with a greater risk of heart attack. The heavier the traffic pollution, the higher the risk of heart attack.
The researchers looked at heart attack risk for 72 hours after exposure to pollution, but found that the risk remained elevated for only six hours. The findings are in line with previous research that has also found air pollution to have an immediate, negative impact on heart health.
Although the overall heart risk of air pollution is short-lived and likely most dangerous to those who are already at risk of heart attack, there’s still good reason to reduce traffic pollution as much as possible. “Given other evidence that exposure to air pollution increases overall mortality and morbidity, the case for stringent controls on pollutant levels remains strong,” wrote epidemiologists Prof. Richard Edwards and Dr. Simon Hales from the University of Otago in New Zealand in an editorial accompanying the study.
Meredith Melnick is a reporter at TIME. Find her on Twitter at @MeredithCM. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.