According to new research, living in a busy city is bad for your heart.

It seems breathing in diesel exhaust fumes at levels typically found in large cities, disrupts important blood vessel functions and could be linked to increased heart attack rates during periods of high air pollution.

Over the last 20 years many studies have shown that the numbers of deaths and hospitalizations due to heart attack and stroke go up as traffic-induced air pollution rises.

Apparently the link between air pollution and cardiovascular disease is strongest for fine-particle pollutants, of which the combustion of fossil fuels from vehicles is a major source.

But until now the underlying factors responsible for air pollution’s effects on the heart and blood vessels were largely unknown.

This latest study by researchers at the Centre for Cardiovascular Science at the University of Edinburgh, provides some suggestions as to what those factors might be.

In the Scottish study researchers found that exposure to diesel exhaust for one hour during exercise caused a significant decrease in the blood vessels’ ability to expand, or dilate.

It was also seen that exposure to the air pollution also decreased levels of an enzyme that helps prevent clots from forming in the blood and possibly causing a heart attack.

Lead researcher Dr. Nicholas Mills, says that low levels of diesel exhaust are having real effects on our blood vessels, and the way in which they function, and may potentially be sufficient to act as a trigger for a heart attack.

Dr. Mills, says short-term exposure to air pollution can worsen existing problems and lead to hospitalization for heart attack and other heart and lung conditions, while long-term repeated exposure increases the risk of death from coronary heart disease, abnormal heart rhythms and heart failure.

The study involved 30 healthy, non-smoking men, aged 20 to 38, who were evaluated during two one-hour tests, two weeks apart.

During each test, the men were randomly assigned to be exposed to either filtered air or diesel exhaust while riding a stationary bicycle for 15-minute intervals while inside a specially built diesel exposure chamber, while diesel exhaust was generated from an idling engine.

During exposure, the particle concentration was kept at a level comparable to curb-side exposure on a busy street in a large city.

At two and then at six hours after being in the chamber, researchers injected one arm of each participant with drugs that cause blood vessels to relax and expand, then measured blood flow in the infused and non-infused arms.

The drugs, known as vasodilators, caused increases in forearm blood flow after exposure to both filtered air and diesel exhaust.

Mills says they found that blood flow fell markedly two hours after diesel exposure, and the reduced response to the vasodilators continued to persist up to six hours later.

The researchers had a particular interest in diesel engines because they generate 100 times more pollutant particles than comparable-sized gasoline engines, and it seems the number of diesel-powered automobiles is on the rise around the world, especially in Europe.

Mills says whether these findings apply to gasoline-powered engines is unclear, since diesel fuel and gasoline are consumed and break down differently during engine operation.

The study is published in the Journal of the American Heart Association.