Study warns even moderate levels of air pollution causes heart damage

By Stephen Beech

Even moderate levels of air pollution can cause heart damage, warns a new study.

Long-term exposure to just low levels of fumes is associated with more advanced coronary artery disease, according to the findings.

Canadian researchers examined the relationship between long-term air pollution exposure and coronary atherosclerosis - known as "hardening of the arteries" - in one of the largest studies of its kind.

Their findings, published in the journal Radiology, showed that, even at moderate levels, long-term exposure to air pollution is associated with more advanced coronary artery disease.

Air pollution is the leading environmental risk factor for heart disease around the world, contributing to around 2.5 million cardiovascular deaths each year.

It plays a major role in causing heart attacks and stroke, according to the World Health Organization (WHO).

Study senior author Kate Hanneman said: "This is one of the largest studies to use cardiac CT to show that air pollution is linked to more advanced coronary artery disease - going beyond calcium scoring to include total plaque burden and obstructive disease - in a population with moderate exposure levels typical of high-income countries."

Previous studies have shown that short-term air pollution exposure, for hours to days, is associated with increased hospital visits for ischemic heart disease, hospital admissions for heart failure and greater use of medical imaging.

Exposure over the longer term - months to years - is linked to increased risks of myocardial infarction, stroke and cardiovascular mortality.

Hanneman's team at the University of Toronto analyzed data from 11,128 adults who had undergone cardiac CT exams from 2012 through to 2023 across three major hospitals in the city.

They linked patients' residential postal codes with air quality data to estimate each person's average exposure to air pollution over the 10-year period prior to CT.

Three markers of coronary artery disease were assessed: calcium score, total plaque burden and obstructive stenosis, or artery narrowing.

The team evaluated the relationship between long-term exposures to two common pollutants found in urban air, ambient fine particulate matter (PM2.5) and nitrogen dioxide (NO2).

PM2.5 sources include vehicle exhaust, industrial emissions and wildfire smoke.

At around 30 times smaller than a human hair, the tiny particles can penetrate deep into the lungs and bloodstream.

NO2 is a harmful gas produced mainly by burning fossil fuels in vehicles, power plants and industrial processes.

For each increase in long-term PM2.5 of one microgram per cubic metre, there was an 11% increase in calcium build-up in the coronary arteries, 13% greater odds of more plaque and 23% greater odds of obstructive disease.

Exposure to nitrogen dioxide showed similar trends, though with smaller effect sizes for every one part-per-billion increase.

Hanneman said: "Medical imaging is emerging as a powerful tool for environmental health research.

"By directly visualizing coronary atherosclerosis, cardiac CT allows us to detect and quantify the cardiovascular effects of long-term air pollution exposure in ways that go beyond traditional risk factors."

She says the findings show that even levels of air pollution below or near regulatory standards and typical urban exposures are associated with early signs of heart disease - often before symptoms appear - and underscore the importance of improving air quality to reduce the risk.

For individual patients, Hanneman believes the findings may open the way to incorporating environmental exposure history into cardiovascular risk assessment, like clinicians would ask about smoking and family history.

She said: "Even at exposure levels below current Canadian air quality standards, long-term air pollution was independently associated with more advanced coronary artery disease - suggesting current regulations may not be fully protective and that air pollution belongs alongside blood pressure, cholesterol and smoking as a modifiable cardiovascular risk factor."

Hanneman noted that what makes it particularly important is the exposure context.

The current 10-year PM2.5 exposure in the study group was well below the current Canadian Ambient Air Quality Standard.

Hanneman said: "The fact that we can detect a measurable signal in coronary atherosclerosis at these levels suggests there may be no clear, safe threshold for cardiovascular harm from air pollution, and that even populations in countries with relatively clean air face meaningful cardiovascular risk from environmental exposure."

She says the research also illustrates the need for prevention as reducing air pollution exposure through policy, urban planning and personal decisions is itself a health intervention.

Hanneman added: "It is also worth noting the connection between air pollution and climate change.

"Because fossil fuel combustion drives both air pollution and greenhouse gas emissions, policies that improve air quality can deliver simultaneous benefits for cardiovascular health and the planet."

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