November 4, 2025

Every marathon runner knows those tough days when legs feel heavy and breathing is hard. Usually, we blame nerves, weather, or diet. But guess what? A fresh study finds that air pollution could be the sneaky villain behind slow finish times! Researchers from Brown University dived into data from millions of marathon finishers in big US races from 2003 to 2019, including New York City, Boston, and Los Angeles. They looked closely at PM2.5 — tiny particles smaller than 2.5 micrometers floating in polluted air. This PM2.5 stuff is what often triggers air quality warnings and health alerts. The findings were striking: for every tiny rise in PM2.5 by 1 microgram per cubic meter, men slowed down by 32 seconds on average, and women by 25 seconds. This means that even moderate pollution can add up to several minutes of slower running. Joseph Braun, an epidemiology pro at Brown, said, "What's notable is that we're looking at people who are all incredibly healthy. But even among really healthy people, air pollution is having an important, albeit subtle, effect on your physiology." Why is this happening? PM2.5 comes from burning things like coal, oil, gas, and even vehicle exhaust. Forest fires and burning wood add to the mix. These tiny particles can sneak deep into your lungs and bloodstream, stirring up trouble like coughing, chest tightness, and inflammation. For people with health problems, these pollutants can worsen asthma or trigger serious events like strokes or heart attacks. In recent years, while some US areas got cleaner air thanks to stricter rules, there’s worry about sudden pollution spikes from wildfires, especially in the West. Also, some pollution controls have been relaxed recently, raising flags among experts. To track pollution during races, researchers used smart machine-learning tools that estimated PM2.5 along marathon routes on race days. Besides air pollution, runners also face heat and humidity challenges. Climate Central’s study of 221 marathons reveals a warming planet means cool, perfect running days are getting rare. So next time you hit the road for a race, remember—the air you breathe could be a secret hurdle slowing your pace!

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Tags: Air pollution, Marathon running, Pm2.5, Brown University, Race Times, Environmental Health,