Long-term exposure to air pollution increases the risk of heart attacks – even at levels below current European limits, experts have warned.

Research on more than 100,000 people followed up for almost 12 years found that exposure to particulate matter in the air led to a higher chance of heart attacks and cases of unstable angina.

Over the course of the study, more than 5,100 people from across Finland, Sweden, Denmark, Germany and Italy suffered one of these heart problems.

In the EU, the current yearly limit for particulate matter with a diameter of 2.5 micrometres or less (known as PM2.5) is 25 microgram/m3. In the US, the figure is much lower at 12 microgram/m3.

Researchers found that a five-microgram/m3 increase in the estimated annual level of PM2.5 was associated with a 13 per cent increased risk of heart attacks and angina.

A 10 microgram/m3 increase in estimated annual level of matter known as PM10 was linked to a 12 per cent increased risk.

These factors held true even when taking into account other possible reasons for heart disease, such as smoking and social deprivation.