Breathing air pollutants raises the risk of having a heart attack, a new review suggests.

Other studies have linked air pollution levels to hospital admissions and deaths from cardiovascular disease. But making that link for heart attacks has been controversial, since the research has been mixed.

In Wednesday's issue of the Journal of the American Medical Association, Dr. Hazrije Mustafic from the Paris Cardiovascular Research Center and his team in France, the U.S. and Montenegro reviewed studies on air pollutants and heart attack risk.

The breathing of pollutants from traffic such as carbon monoxide, nitrogen dioxide, sulphur dioxide and tiny soot-like particles for up to a week boosted heart attack risk by one to three per cent in the following week.

The size of the link was relatively small when compared to risk factors such as smoking and high blood pressure, the researchers said.

Since nearly everyone in cities is exposed to the pollutants, "an improvement in air quality could have a significant effect on public health," the study's authors concluded.

As for how the pollutants could cause harm, the researchers pointed to inflammation, which is associated with heart attacks.

Poor air quality could also increase the heart rate, speed up atherosclerosis, or hardening of the arteries, and make the blood more likely to form potentially dangerous clots, they speculated.

Ozone was the only type of air pollutant that was not implicated in the increased risk.