The Air We Breathe, The Arteries We Clog

TORONTO, ON – December 04, 2025 – For millions living in urban centers, the daily haze of traffic and industry is an accepted part of the landscape. But a landmark study presented today reveals this ever-present pollution is exacting a hidden, dangerous toll on our cardiovascular health, hardening our arteries long before any symptoms appear. The findings, unveiled at the annual meeting of the Radiological Society of North America (RSNA), link long-term exposure to common air pollutants with more advanced coronary artery disease, even at levels currently considered safe by many regulatory bodies.

The large-scale study of over 11,000 adults in Toronto provides some of the most definitive evidence yet that the air we breathe is a direct and modifiable contributor to the world's number one killer: heart disease. Using advanced cardiac CT imaging, researchers have peered inside the body's most critical plumbing and found a troubling connection between air quality and the silent buildup of arterial plaque, with significant and surprising differences in how men and women are affected.

The Invisible Damage from "Safe" Air

The research team, led by investigators from the University of Toronto and University Health Network (UHN), focused on two ubiquitous urban pollutants: fine particulate matter (PM2.5) and nitrogen dioxide (NO2). PM2.5, particles 30 times smaller than a human hair, comes from sources like vehicle exhaust and industrial emissions, and can penetrate deep into the lungs and bloodstream. NO2 is a harmful gas primarily from burning fossil fuels.

By linking patients' residential postal codes with ten years of air quality data, the researchers could estimate each individual's long-term exposure. They then analyzed cardiac CT scans for three key markers of coronary artery disease: coronary artery calcium (CAC) score, total plaque burden, and obstructive stenosis (severe artery narrowing). The results were stark.

"Even at low exposure levels, air pollution is associated with more plaque in the coronary arteries," stated Dr. Felipe Castillo Aravena, the study's lead author and a cardiothoracic imaging fellow. The data showed that for each single microgram per cubic meter increase in long-term PM2.5 exposure, the odds of obstructive disease jumped by 23%, with an 11% increase in calcium buildup and a 13% greater chance of more plaque.

Crucially, the study notes these associations were found at exposure levels "below or near regulatory standards." This finding challenges the adequacy of current air quality guidelines. For instance, while Canada's annual standard for PM2.5 is 8.8 µg/m³ and the U.S. standard is 9.0 µg/m³, the World Health Organization (WHO) recommends a much stricter guideline of 5 µg/m³. This study suggests that even in cities meeting national standards, residents may still be incurring significant, cumulative cardiovascular damage, effectively redefining what we should consider a "safe" environment.

A Tale of Two Hearts: Pollution's Gender-Specific Impact

Perhaps one of the most compelling aspects of the research is the discovery that air pollution does not affect everyone's heart in the same way. The study identified distinct patterns of damage between women and men, pointing toward a need for more nuanced, sex-specific approaches in both research and clinical practice.

In women, higher long-term exposure to fine particulate matter was linked to higher calcium scores and, notably, more severe narrowing of the arteries (stenosis). In men, while higher PM2.5 exposure was also associated with higher calcium scores, it was more strongly linked to a higher overall plaque burden. Nitrogen dioxide exposure was associated with coronary artery disease in both sexes.

These differences open a new frontier of investigation. "This is one of the largest studies to link long-term gaseous and particulate air pollution at contemporary exposure levels with multiple markers of coronary artery disease assessed by cardiac CT," said Dr. Kate Hanneman, the study's senior author, a cardiac radiologist and vice chair of research at the University of Toronto and UHN. She emphasized the need to understand why these associations differ.

While the study did not establish causality, Dr. Castillo noted that biological factors, such as hormonal differences and vascular reactivity, alongside social and behavioral patterns, could be contributors. This aligns with a growing body of evidence showing that women's cardiovascular systems can respond differently to environmental stressors. Dr. Hanneman's previous research, which found that the effects of air pollution on heart muscle scarring were largest in women, suggests a consistent pattern of sex-specific vulnerability that demands further exploration.

Advanced Imaging: Making the Invisible Visible

This study is a powerful example of how technology is being implemented to bridge environmental health and clinical medicine. The use of cardiac CT is central to its findings, allowing for the non-invasive quantification of coronary artery disease in its earliest stages—a critical window for intervention. By measuring calcium and plaque before a patient experiences chest pain or a heart attack, clinicians can identify at-risk individuals who might otherwise be overlooked by traditional risk calculators.

The methodology itself—linking vast datasets of medical images with longitudinal, location-based environmental data—represents a sophisticated application of data science in public health. It transforms the radiologist's role from simply diagnosing an individual's condition to helping uncover the population-level environmental drivers of disease.

As Dr. Hanneman highlighted, "Heart disease is the number one cause of death globally. The results of this study add to the growing body of evidence that air pollution is a modifiable cardiovascular risk factor." This perspective positions advanced imaging not just as a diagnostic tool, but as a powerful research instrument capable of informing public policy and preventative health strategies on a massive scale. Knowing a patient's long-term pollution exposure could one day become a standard part of their cardiovascular risk assessment, refining and personalizing care.

The Urban Mandate: From Data to Action

With the Toronto study serving as a clear case study for cities worldwide, the implications for urban planning and public health policy are profound. If residents are developing heart disease from air quality levels that meet current legal standards, then those standards are not sufficient to protect public health. The findings provide a strong, data-driven mandate for policymakers to accelerate efforts to clean the air in our cities.

Initiatives like Toronto's TransformTO climate action plan, which aims to reduce emissions through cleaner transportation and greener buildings, are a step in the right direction. However, this research suggests such efforts are not merely environmental niceties but urgent public health imperatives. Reducing vehicle emissions, transitioning away from fossil fuels, and designing cities that promote active transport are direct interventions to protect the cardiovascular health of millions.

The study reinforces that air pollution is not a distant, abstract threat but a personal one, silently shaping the health of our hearts with every breath we take. As our ability to measure its impact with such precision grows, the responsibility to act on that knowledge becomes impossible to ignore.