Road pollution link to heart attacks and strokes

Scientists have found new evidence that pollution from cars, lorries and buses triggers a chain reaction in the blood that leads to potentially deadly hardening of the arteries.

British heart experts said the findings reinforced earlier advice that people with chronic lung or heart disease should avoid staying outside for long periods when pollution levels were high.

Although the link between pollution and heart disease and stroke has long been known, the study is the first to explain how the fine diesel particles "conspire" with artery-clogging cholesterol to switch on the genes that cause blood vessel inflammation.

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Dr Andrew Nel, who led the study at the University of California, Los Angeles, said: "When you add one plus one it normally totals two. But we found that adding diesel particles to cholesterol fat equals three. "Their combination creates a dangerous synergy that wreaks cardiovascular havoc far beyond what's caused by the diesel or cholesterol alone."

The findings, published in the journal Genome Biology, are based on laboratory studies of human tissue. The scientists combined diesel particles and the "bad" form of cholesterol in a test tube, and added them with cells taken from the inner lining of human blood vessels.

A few hours later, DNA tests of the human cells showed that the diesel particles were working in tandem with cholesterol to encourage inflammation of the blood vessels. The same effect was later seen in living mice. "Exactly how air pollutants cause cardiovascular injury is poorly understood," said Dr Nel. "But we do know that these particles are coated with chemicals that damage tissue and cause inflammation of the nose and lungs.

"Vascular inflammation in turn leads to cholesterol deposits and clogged arteries which can give rise to blood clots that trigger heart attack or stroke."

Cathy Ross, a spokesman for the British Heart Foundation, said: "We already know that prolonged exposure to air pollution results in a small increase in risk of death from heart disease and stroke.

"This study provides evidence that one reason for the increased risk may be because small particles from the air pollution reach the bloodstream, where they interact with fats, making them more likely to be trapped in the vessel wall, leading to the fatty build upcalled atherosclerosis.

The BHF is funding research into this area to identify how risk may be reduced.

"For most people, we know that everyday measures such as eating a healthy diet low in saturated fat, taking regular physical activity and giving up smoking will have more impact on reducing the risk of developing heart disease.

"But, anyone with chronic lung disease or coronary heart disease should avoid staying outside for long periods when pollution levels are high."