Diesel fumes raise the risk of heart attacks and strokes by damaging protective cholesterol in the body, research suggests. Breathing in black carbon – the tiny sooty particles particularly linked to diesel exhaust – reduces levels of ‘good’ HDL cholesterol thought to protect the heart and arteries, experts said. A study of more than 6,500 people in the US found that just three months of exposure to high air pollution was enough to see HDL levels fall. Medical experts are increasingly aware of the impact of diesel air pollution fumes on human health, including the risk of asthma, dementia and some forms of cancer. Emerging evidence suggests it also raises the risk of heart disease, but the new study explains why it might do so. Study leader Dr Griffith Bell, from the University of Washington in Seattle, said the damage can happen at ‘comparatively low levels’ of air pollution. He said, “Our study helps strengthen the biological plausibility of the link between traffic related air pollution and cardiovascular disease. We are slowly beginning to understand some of the biology of how that link works.” Fumes and toxins in polluted air are estimated to contribute to the deaths of 40,000 people in Britain every year. The UK is notoriously bad at controlling air pollution, with 37 cities across Britain persistently breaching legal limits of air toxins. It is due later this month to publish new air quality plans, after being ordered to do so by the High Court. Diesel cars have been promoted since the 1970s as an environmentally-friendly choice because they emits less carbon dioxide, the greenhouse gas which causes global warming. Successive governments have put tax incentives on diesel cars, allowing drivers to pay less vehicle excise duty. But in recent years scientists have realised that diesel also produces more of the tiny particles and nitrogen oxides that are damaging to human health. Black carbon is one of these particles that are emitted in high levels from diesel engines. Dr Bell, whose work is published in the journal Arteriosclerosis, Thrombosis & Vascular Biology, suspects black carbon attacks HDL. This results in higher quantities of harmful fat forming in vessels and raising the risk of a clot, blocking off blood supply to the heart or brain. In a study of 6,654 middle aged and elderly Americans, his team found those living in areas with high levels of traffic related air pollution tended to have lower HDL levels. Higher exposure to black carbon, the sooty emissions from diesel engines and a marker of vehicle pollution, over a period of a year was significantly associated with less HDL. More exposure to other particulate matter for just three months was also linked with a lower HDL particle number. Dr Bell said the lower HDL observed with greater air pollution “may put individuals at a higher risk for cardiovascular disease down the line”. He added, “This is the first large observational study to suggest an association between air pollution exposure and HDL particle number. This study contributes to the hypothesis that air pollution may act through HDL to contribute to cardiovascular disease at comparably low levels found in developed countries.” Professor Sir Nilesh Samani, medical director of the British Heart Foundation Medical Director Nilesh Samani said, “There is an urgent need to fund more research that looks in to the dangerous effects of air pollution on the cardiovascular system. This silent killer is related to 40,000 deaths in the UK each year, with eight in ten caused by a heart attack or stroke. This is an interesting study showing an association between higher air pollution and lower levels of HDL-cholesterol, often called ‘good cholesterol. It is still too early to say how these findings might fit in to the wider picture, but the underlying message is the same – air pollution poses a serious risk to heart health.” Anna Heslop, a lawyer at Client Earth, which has taken the government to court several times over air pollution, said, “Government ministers in the UK should read this study with concern. The research focuses on one of the dangerous pollutants spewed from dirty diesel vehicles that blight the air in towns and cities across the UK every day. With the new air quality plans, due by the 24 April, that the Government was forced to produce by our legal action in the High Court, ministers have the opportunity to put our health above the interests of the diesel lobby.”