Air pollution could be directly linked to irregular heartbeat and blood clots in the lungs, but the correlation is less clear for heart attack and stroke.

New research suggests that high levels of air pollutants are linked to heart disease, but researchers are not sure why, a BMJ-British Medical Journal news release reported.

To make their findings the researchers looked at the Myocardial Ischaemia National Audit Project (MINAP), which studies the short-term effects of pollution on heart attack and stroke risk. They also looked at data from the Office of National Statistics (ONS).

"Some 400,000 heart attacks recorded in MINAP; more than [two] million emergency admissions for cardiovascular problems; and 600,000 deaths from a heart attack [or] stroke were linked to average levels of air pollutants over a period of 5 days using data from the monitoring station nearest to the place of residence," the news release reported.

Pollutants that were taken into account were "carbon monoxide, nitrogen dioxide, particulate matter (PM10 and PM2.5), sulphur dioxide, and ozone," the news release reported.

Only Nitrogen Dioxide was found to be linked to a higher rate of hospital admissions for cardiovascular disease. The team did find a link between particulate matter levels and the risk of atrial fibrillation and pulmonary embolism.

The researchers were not able to find a short-term link between pollution and heart attack and stroke.

About three million people across the globe are believed to die from pollution-related conditions every year. These are usually caused by heart attack or stroke.

"The current lack of consistent associations with contemporary UK data may suggest that as the fog begins to clear, the adverse health effects of air pollution are starting to have less of an impact and are more difficult to delineate," the researchers said in the news release.