Even 'Safe' Levels of Air Pollution Linked to Coronary Artery Disease, Especially in Women
Key Insights
Long-term exposure to fine particulate matter and nitrogen dioxide (search) at levels below current regulatory limits is associated with advanced coronary artery disease (search), according to a study of over 11,000 adults in Toronto.
Women showed significantly greater odds of serious artery narrowing with higher pollution exposure, while the association in men was not statistically significant.
A separate review of 95 global studies found that 67% showed significant links between low-level PM2.5 (search) exposure and cardiovascular harm, with vulnerable populations at heightened risk.
Even the relatively clean air typical of North American cities may damage heart arteries, particularly in women, according to new research that challenges the notion of a "safe" level of air pollution for cardiovascular health.
A study published in the June 2026 issue of Radiology found that long-term exposure to common air pollutants from automobiles, industrial activity, and fossil fuel burning is linked to advanced coronary artery disease (search), even at concentrations near or below current regulatory safety limits. The findings add weight to a growing body of evidence connecting air pollution to heart disease and suggest there may be no threshold below which air quality can be considered entirely safe.
"There may be no 'floor' at which air quality can be considered entirely safe for the human heart," said cardiac surgeon Salil Deo of Case Western Reserve University School of Medicine in Cleveland, who was not involved in the work.
Imaging Reveals Subclinical Disease Progression
Rather than focusing on acute cardiovascular events like heart attacks, the study used heart scans to demonstrate how long-term pollutant exposure is associated with the buildup and progression of coronary artery disease (search). Kate Hanneman, a cardiac radiologist at the University of Toronto, and colleagues tracked more than 11,000 adults in Toronto and surrounding areas who underwent heart scans between 2012 and 2023. Each participant's residential history was linked to air quality data from the preceding decade to estimate long-term exposure.
The team focused on two pollutants: fine particulate matter (PM2.5 (search)) and nitrogen dioxide (search) (NO₂). Fine particulate matter consists of tiny airborne particles small enough to be inhaled deep into the lungs, while NO₂ is a gas produced mainly by vehicle traffic and fossil fuel combustion. Both can contribute to inflammation affecting the heart and blood vessels. Most participants were exposed to levels below Canada's annual air quality standards and within ranges commonly seen across North American and European cities.
The higher the exposure to fine particulate air pollution, the more signs of heart artery disease the researchers observed on scans. As exposure increased, calcium buildup in the heart arteries was higher and plaque was more common. The odds of serious artery narrowing were greater, especially in women. The scans showed similar, but smaller, effects for NO₂.
"There was no level at which the risk clearly flattened or disappeared," Hanneman said.
Sex-Based Differences Emerge
In men, the association between severe artery narrowing and higher pollutant exposure was not statistically significant, though both sexes showed more calcium and plaque as pollution increased.
"The pattern is consistent with earlier research," Hanneman said. "It may reflect biological differences, such as breathing rates relative to body size, hormone-related inflammatory responses and higher levels of noncalcified, harder-to-detect plaque in women."
Adjusting for established cardiovascular risk factors such as high blood pressure and cholesterol weakened the association, suggesting that pollution may partly work by worsening these conditions.
Broader Evidence from Global Research
A separate review published in Environmental Pollution reinforces these concerns. University of Mississippi researchers examined 95 studies from around the world on the impact of low-level PM2.5 (search) exposure on cardiovascular health. Some 67% of the studies showed significant associations with heart disease.
"If we were looking to make a regulation that was just focused on human health, our reviews suggest that the regulation should be lowered because we are seeing cardiovascular impacts," said Courtney Roper, assistant professor of environmental toxicology at the University of Mississippi.
Certain populations—including older adults, very young children, people with preexisting heart conditions, impoverished individuals, and marginalized populations—were found to be particularly vulnerable to low-level exposure.
"The risk is also dependent upon the source of PM2.5 (search)," said James Stewart, associate professor of pharmacology at the University of Mississippi. "Whether it's traffic pollution or manufacturing industrial pollution, or even rural pollution, where you have harvesting or plowing generating dust, that can impact human health on so many levels."
Clinical and Public Health Implications
Coronary artery disease (search) develops when calcium deposits and plaque buildup narrow the heart's arteries, raising the risk of heart attack. Earlier studies have associated air pollution with heart attacks and strokes, and experts estimate air pollution contributes to 4 million to 6 million of the 20 million cardiovascular deaths worldwide each year.
The findings do not suggest that most people need to change their daily routines. However, during heavy pollution episodes, such as wildfire smoke events, people at higher risk—including those with heart disease, diabetes, or advanced age—may benefit from staying indoors, using air filtration, or wearing an N95 mask outdoors, Deo said.
"Reducing long-term exposure and moving toward stricter air quality standards could meaningfully protect cardiovascular health," Hanneman said. "It's an intervention that benefits both public health and the planet."
Roper and Stewart emphasized the importance of public awareness. High-efficiency particulate air (HEPA) filters can remove particles as small as 0.03 microns, and N95 masks can filter PM2.5 (search) pollution. Air quality reports are available daily on most weather applications.
"Public awareness is the next step," Stewart said. "We need to increase education and general public awareness around this problem. Health care workers should be paying attention to fluxes in pollution to better address health needs of patients. The question is not just, 'How can we treat exposure?' but 'How can we prevent it?' That starts with public awareness."