Even Clean Air Isn’t Risk-Free: Low-Level Air Pollution Tied to Coronary Atherosclerosis in Canada

Introduction
While smoggy skylines in industrial megacities dominate public discourse around air pollution, a new study from Canada suggests that even relatively low levels of particulate matter (PM2.5) are significantly associated with coronary artery calcium (CAC), plaque burden, and obstructive coronary artery disease (CAD). The findings, presented at the 2025 Society of Cardiovascular Computed Tomography (SCCT) meeting, challenge existing perceptions of what constitutes “safe” air quality and call for a re-evaluation of how we monitor and manage cardiovascular risk.

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Pollution and Plaque: The Study at a Glance

Researchers from the University of Toronto conducted a retrospective analysis of 11,128 patients undergoing cardiac CT for suspected CAD across outpatient centers in Canada between 2014 and 2023. The median age was 59.1 years, with 51.7% of participants being men.

Participants were exposed to a median PM2.5 concentration of 7.5 µg/m³—below the World Health Organization (WHO) safety thresholds. Yet the results were revealing:

• Every 1 µg/m³ increase in PM2.5 was associated with:

  • 10.7% higher CAC score

  • 12.5% greater odds of increased total coronary plaque

  • 22.6% higher odds of obstructive CAD (≥70% stenosis)

Source: American Heart Association

Sex-Specific Differences

The study found distinct gender-based effects:

• In women, higher PM2.5 levels correlated with:

  • Elevated CAC scores

  • Increased risk of obstructive CAD

  • No significant change in total plaque burden

• In men, higher PM2.5 levels were linked to:

  • Increased CAC scores

  • Elevated total plaque burden

  • No significant increase in obstructive CAD

These nuances highlight the importance of sex-stratified cardiovascular risk assessments in environmental health studies.

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Why This Matters—Even in "Clean" Countries

Most study participants lived in areas with pollution levels considered "safe" by global standards. Still, they showed clear subclinical markers of atherosclerosis. This adds weight to recent calls by the World Health Organization to lower the annual safe limit of PM2.5 from 10 to 5 µg/m³.

Lead investigator Dr. Kate Hanneman emphasized the importance of this finding:

“We see the association at relatively low exposure levels. This is really important and distinct from areas like China where patients typically have much higher exposure levels.”

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Implications for Clinical Practice

These findings suggest several key takeaways for clinicians:

• Air pollution should be considered a modifiable cardiovascular risk factor, even at low ambient levels.

• CAC scanning could be more widely utilized in individuals with occupational or residential exposure to pollution.

• Sex-specific patterns of atherosclerosis progression warrant more individualized risk stratification.

Furthermore, these insights may catalyze public health action toward:

• Improving air quality monitoring

• Implementing urban planning to reduce exposure zones

• Educating both patients and providers about environmental cardiovascular risk

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Key Takeaways

• Even low levels of air pollution (PM2.5 < 10 µg/m³) are associated with higher CAC, plaque burden, and obstructive CAD.

• The association is sex-specific, affecting plaque burden in men and obstructive CAD in women.

• These data challenge current “safe” pollution limits and suggest that environmental exposure should be integrated into cardiovascular risk assessments.

• CAC scanning may be a useful tool for early detection in patients with chronic exposure to pollution.