Even moderate levels of air pollution have now been linked to increased risk of heart attacks in people with heart disease. That's according to new research presented Sunday at the American Heart Association's annual conference.
Researchers analyzed 20 years of data on 16,000 heart attacks treated at Intermountain Healthcare in Utah. They matched the medical records to weather data on fine particulate matter 1 in the air. That's the kind of pollution that comes from burning fuel in vehicles or power plants, or other sources, such as wildfires.
They found that elevated risk of heart attacks began at a pollution level that U.S. environmental regulators consider "moderate." The threshold was around 25 micrograms of fine particles per cubic meter, which translates to an air quality index of 78 on the Environmental Protection Agency's scale. That's considered a yellow warning—acceptable air quality for most people but potential concern for a "very small number of people who are unusually sensitive to air pollution," according to the EPA.
The analysis is the first to link the most dangerous types of heart attacks, where an artery is entirely blocked, to short-term exposure to moderately polluted air, said Dr. Kent Meredith, an interventional cardiologist at Intermountain and lead investigator on the study. Researchers didn't find an increased risk for people without heart disease, and they didn't find risk at lower levels of pollution.
How does air pollution trigger heart attacks? "When you have exposure to that high a level of inhaled fine particulate matter, you’re triggering your immune system," Meredith said. The immune response can cause plaque built up in the arteries to become unstable and dislodge, clogging arteries and blocking blood flow to the heart.
In the Salt Lake City area, where Intermountain is based, cold air masses tend to settle in the valley in January and February, Meredith said, bringing smog with them. "It’ll look pretty gray, the air is thick and brown," he said. "In mountains a thousand feet above that, you can actually see that layer."
For people with heart disease, the study suggests limiting time outdoors and exercise at relatively modest levels of pollution. The risk to people with heart disease increases with more particulates above that threshold. "The data suggests that you can recommend that patients with heart disease are more vulnerable for those types of events when they’re exposed to higher levels of pollution," Meredith said.