Heart attack survivors are more likely to die over the following years if they live in an area with higher levels of pollution.

Patients released from the hospital following a heart attack are more likely to die over the following years if they go home to an area with higher levels of air pollution, according to a new study in the European Heart Journal.

By air pollution, the study refers specifically to particulate matter that's 2.5 micrometers in diameter (PM2.5). No significant results were found for larger particles or for the presence of nitrogen oxide in the air. But reducing the concentration of PM2.5 to a baseline level, absent human contributions, could reduce post-heart attack mortality by 12 percent, according to the authors.

To arrive at this data, they followed over 150,000 patients in England and Wales, cross-referencing their health records with average air pollution levels for their postcode (that's British for zipcode). At the study's end, a quarter had passed away; the researchers estimate that 4,783 of those deaths occurred prematurely and can be attribtued to the influence of air pollution.

By looking at postcodes, they hoped to get a clearer picture of how the area in which the patients live might be affecting their cardiovascular health. (Although they didn't look at the specific cause of death for patients who passed away within the follow-up period, the majority were assumed to be heart-related, as air pollution has previously been shown to negatively affect cardiovascular health.)

What's interesting about their focus on the patient's location, though, is that one of the aims of the study was to evaluate whether air pollution might be contributing to the socioeconomic disparities seen in mortality following heart attacks: Multiple studies have established that patients with lower income and less education are more likely to die following a heart attack. The same has been established for people living in poorer communities, which are also known to suffer disproportionately from poor air quality. 

But after accounting for factors like smoking and diabetes, the researchers found little support for air pollution's ability to explain the steady decline of recovery rates with lowered socioeconomic status. Something else, yet to be fully understood, must be behind that association; air pollution is more of an equal opportunity health risk. 

So how to reduce exposure, and thus at least this known risk? In the U.S., according to the EPA , major sources of PM2.5 include traffic, wood burned in stoves and fireplaces, field and forest burning, and, to a lesser extent, industrial production. Absent man's influence, its concentration in the air would stand at about 4 µg/m3; in this study, mean concentrations ranged from 8 to 14. Federal standards in the U.S. were officially updated last month to limit the PM2.5 concentration in the air to 12 µg/m3, and most of the country is believed to have already met this goal. That's not terrible news, because the authors estimate that for every 10 µg/m3 of increased PM2.5 pollution, the risk of death following a heart attack increases by 20 percent. Then again, 16 percent increased mortality isn't the most inspiring of minimum standards.

This post originally appeared on The Atlantic.

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