Air pollution doesn’t raise heart attack risk in smokers — because they’re already ‘self-intoxicating with pollutants’

BARCELONA, Spain — A new study has found a causal relationship between air pollution and heart attacks. While the impact of pollution on health may not be a surprise, researchers note they only found a correlation among non-smokers. This suggests that smokers may actually be more resilient to the toxic effects of smog.

“The correlation between air pollution and heart attacks in our study was absent in smokers. This may indicate that bad air can actually cause heart attacks since smokers, who are continuously self-intoxicating with air pollutants, seem less affected by additional external pollutants,” says study author Dr. Insa de Buhr-Stockburger of Berlin Brandenburg Myocardial Infarction Registry (B2HIR), in a media release.

More specifically, researchers looked for associations between nitric oxide, particulate matter with a diameter less than 10 µm (PM10), and weather and the local rate of heart attacks in Berlin. Nitric oxide is a byproduct of combustion at high temperatures, usually from diesel vehicles. Similarly, combustion is also a source of PM10. Other PM10 sources include abrasion from brakes and tires as well as dust.

Poor air quality did not increase heart attacks among smokers

The project included 17,873 patients who had a heart attack between 2008 and 2014 and took part in the B2HIR. The team extracted daily heart attack statistics from the B2HIR database, as well as baseline patient characteristics such as sex, age, smoking status, and diabetes. Berlin’s senate provided information on daily PM10 and nitric oxide concentrations. Information regarding weather (sunshine duration, minimum and maximum temperature, precipitation) came from the Berlin Tempelhof weather station.

Study authors analyzed any and all associations between the incidence of heart attacks and average smog levels on that particular day, the previous day, and an average of the three preceding days among all patients and according to baseline characteristics. Researchers also performed additional analyses focusing on any associations between the incidence of acute myocardial and weather patterns.

All that research led scientists to find heart attacks were significantly more common on days with high nitric oxide concentrations. They noted a one-percent higher heart attack incidence rate for every 10 µg/m3 increase. Heart attacks were also more common whenever there were higher average PM10 concentrations over the three preceding days (a 4% higher incidence for every 10 µg/m3 increase). Notably, though, nitric oxide and PM10 concentrations did not affect heart attack rates among smokers.

What about the weather?

Heart attack rates displayed a strong relationship to the maximum temperature, showing a six-percent incidence drop for every 10°C (50°F) rise in temperature. The researchers did not see an association between either sunshine duration or precipitation.

“The study indicates that dirty air is a risk factor for acute myocardial infarction and more efforts are needed to lower pollution from traffic and combustion. Causation cannot be established by an observational study. It is plausible that air pollution is a contributing cause of myocardial infarction, given that nitric oxide and PM10 promote inflammation, atherosclerosis is partly caused by inflammatory processes, and no associations were found in smokers,” Dr. de Buhr-Stockburger concludes.

The study authors are presenting their findings at ESC Congress 2022.

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