brown.edu
Marathon runners are often meticulous about their gear, nutrition, and training—but air quality may be an overlooked factor influencing performance. A new study by researchers at Brown University, published in Sports Medicine, has revealed that higher levels of fine particulate matter in the air on race day are linked to slower marathon finish times.
The study analyzed data from over 2.5 million runners across nine major U.S. marathons—including Boston, Houston, and Los Angeles—held between 2003 and 2019. Researchers combined public finish-time data with a sophisticated spatial-temporal model developed by Allan Just, an associate professor of epidemiology and environment and society at Brown University, to measure levels of fine particulate matter along marathon routes.
The findings showed that for every 1 microgram per cubic meter (µg/m³) increase in fine particulate matter, male runners’ finish times were an average of 32 seconds slower, while female runners were 25 seconds slower. The effects were more pronounced in faster-than-median runners, suggesting air pollution has a greater impact on those pushing themselves harder.
Lead author Elvira Fleury, who conducted the research while earning her Master of Public Health degree at Brown, emphasized the importance of these results. “For marathon runners trying to achieve a personal record, every second matters,” she said.
Fine particulate matter, or PM2.5, refers to microscopic air pollution particles smaller than 2.5 microns in diameter. These particles are generated by sources such as vehicle emissions, industrial activities, forest fires, and agricultural waste burning. PM2.5 is small enough to penetrate the lungs and bloodstream, contributing to cardiovascular and respiratory issues.
Previous research has shown that air pollution is associated with mortality, heart disease, and lung disease. This study adds a new dimension by demonstrating that even highly fit individuals, like marathon runners, are not immune to the effects of air pollution. “People who can complete a marathon are generally quite healthy, and we can assume they have honed their cardiorespiratory fitness,” said Joseph Braun, a professor of epidemiology at Brown. “This study revealed a negative impact from air pollution, even at levels below current health-based standards, on these very healthy people.”
The findings suggest that ongoing efforts to reduce pollution—through regulation of power generation, transportation, and industry—could benefit not only overall public health but also athletic performance. For runners and athletes looking to optimize race-day conditions, factoring in air quality may be a consideration worth adding to the list.