Air pollution exposure raises cardiac death rate

By Helen Albert, Senior medwireNews Reporter

Long-term exposure to high levels of particulate matter with a diameter of 2.5 mm or below (PM_2.5) increases a person's chance for dying following a heart attack, show results from a large UK study.

These findings add to those of previous studies showing that exposure to high levels of air pollution increases the risk for heart and lung disease, as well as overall mortality, say the researchers.

As reported in the European Heart Journal, Cathryn Tonne and Paul Wilkinson (London School of Hygiene and Tropical Medicine) used data from the Myocardial Ischaemia National Audit Project (MINAP) to assess the impact of air pollution exposure on mortality following admission to hospital with acute coronary syndrome (ACS; including ST and non-ST elevation myocardial infarction).

In total, 154,204 patients from England and Wales were included in the study. The patients had an average follow-up time of 3.7 years after admission, and during this period 39,863 patients died.

Air pollution exposure was calculated using a combination of postcode data and information on air pollution levels during the time the patients were being followed up, collected by the Department for Environment Food and Rural Affairs.

The researchers found that people who were exposed to high levels of PM_2.5, mostly produced by road traffic and industrial emissions, had a significantly increased risk for dying following hospital admission for ACS.

Specifically, each 10 µg/m³ increase in PM_2.5 level was associated with a significant 20% increase in mortality rates following admission for ACS.

Notably, a similar association was not observed for exposure to larger particles or nitrogen oxides.

Tonne and Wilkinson estimate that reducing PM_2.5 exposure to that from natural sources alone could reduce mortality in this cohort by 12%, reducing the number of early deaths per year from exposure to man-made PM_2.5 by 4783.

There is a known link between high air pollution exposure and low socioeconomic class, but the authors found that PM_2.5 exposure only explained a small amount of the difference in survival after ACS in people of different socioeconomic classes when other factors such as smoking and diabetes were accounted for.

"The implication is that while reducing levels of PM_2.5 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," commented Tonne in a press statement.

"There are likely to be many other factors that are more important than PM_2.5 exposure in explaining socioeconomic inequalities in prognosis, and this requires further investigation."

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