London School of Hygiene & Tropical Medicine

There has been growing evidence that exposure to fine particulate air pollution is linked to the development of heart disease, but few studies to date have looked at its effect on survival after heart attacks. This study, carried out by researchers at the London School of Hygiene & Tropical Medicine, is the largest yet to investigate this association

Researchers compared air pollution data to the records of 154,204 patients who survived hospital admission for acute coronary syndrome in England and Wales between 2004 and 2007. They found that death rates after leaving hospital were higher among patients who lived in areas with increased exposure to PM2.5 – tiny particulate matter thought particularly damaging to health because it can penetrate deep into the lungs. PM2.5 is caused by emissions from road traffic and industry, including power generation.

Dr Cathryn Tonne, lecturer in environmental epidemiology at the London School of Hygiene & Tropical Medicine says: “We found that for every 10 microgram increase in PM2.5 per cubic metre of air, there was a 20% increase in the death rate. For example, over one year of follow-up after patients had been admitted to hospital with acute coronary syndrome, there would be 20% more deaths among patients exposed to PM2.5 levels of 20 micrograms per cubic metre of air, compared to patients exposed to levels of half that amount.”

Dr Tonne and her colleague Paul Wilkinson, professor of environmental epidemiology at the School, estimate that death rates would be reduced by 12% among acute coronary patients if they were not exposed to this man-made pollution. This translates to 4,783 early deaths among the group studied caused by exposure to particulate matter from man-made sources.

The researchers state that patients living in London had the highest exposure to air pollution levels. They also report that patients from poorer backgrounds often live in more deprived areas with higher levels of air pollution, and after being diagnosed with heart problems they tend to do less well than patients of a higher socioeconomic status.

According to Dr Tonne: “This raises the possibility that exposure to air pollution may explain, in part, the differences in prognosis among heart attack patients from different backgrounds.

“Our findings confirm an association between particle matter and increased rates of death in heart attack survivors. Our findings also show that this particulate matter exposure contributes only a small amount to differences in survival after heart attacks among people living in areas with different socioeconomic conditions after accounting for factors such as smoking and diabetes.

“The implication is that while reducing levels of air pollution will lead to increased life-expectancy and is an important public health priority, it isn’t likely to reduce socioeconomic inequalities in prognosis very much. There are likely to be many other factors that are more important in explaining socioeconomic inequalities in prognosis, and this requires further investigation.”

Publication

• Cathryn Tonne and Paul Wilkinson. Long-term exposure to air pollution is associated with survival following acute coronary syndrome. European Heart Journal. doi:10.1093/eurheartj/ehs480

Image: London traffic. Credit: Anne Koerber