The hearts of people who live in polluted areas are weaker than those who regularly breathe cleaner air, according to a new study.

Researchers said they found evidence of harmful effects even when levels of pollution associated with diesel vehicles were less than half the safety limit set by the European Union.

This showed the current permissible levels of air pollution were “not safe and should be lowered”, a cardiologist involved in the study said. When walking on the pavement, people should stay as far away from the curb as possible to reduce exposure to exhaust fumes.

In the new study, researchers used magnetic resonance imaging to examine the hearts of 4,255 people with an average age of 62.

The size and function of parts of their hearts were then compared with the annual average level of fine particles of pollution, known as PM 2.5, at their home address.

Dr Nay Aung, a cardiologist at Queen Mary University of London, said: “We found that as PM2.5 exposure rises, the larger the heart gets and the worse it performs. 

“Both of these measures are associated with increased morbidity and mortality from heart disease.”

“There is strong evidence that particulate matter emitted mainly from diesel road vehicles is associated with increased risk of heart attack, heart failure and death,” he said.

The study found every 5 microgram per cubic meter increase in exposure to PM2.5 was associated with a 4 to 8 per cent increase in the size of the heart's left ventricle and a 2 per cent decrease in its pumping power.

Dr Aung, who presented the research at the European Association of Cardiovascular Imaging conference, advised people to avoid times and places where there were high levels of pollution.

"If you want to cycle into work and there is heavy traffic around that time then try to find a quieter route," he said.

"Walk on the part of the pavement furthest from cars to reduce the amount of pollution you breathe in.

"Those with cardio-respiratory diseases should limit the time spent outdoors during highly polluted periods such as rush hours."

The process by which air pollution harms the body has been poorly understood. Until recently it was not known if fine particles could pass through the lungs into the bloodstream.

However, a study in which volunteers inhaled gold nanoparticles showed it was possible for this to happen with gold showing up in their blood and urine 15 minutes after they had breathed it in. The particles were still there up to three months later.

Dr Aung said the heart problems of those in the polluted areas “appears to be driven by an inflammatory response – inhalation of fine particulate matter causes localized inflammation of the lungs followed by a more systemic inflammation affecting the whole body”.