Air pollution is slowing down marathon runners, study finds

Higher levels of nitrogen dioxide on race day are linked to slower marathon times, particularly among non-elite runners, new research suggests.

Air pollution added minutes to marathon runners' finishing times across six major races, a new study has found.

Runners in the Berlin, Boston, Chicago, London, New York City and Tokyo marathons have seen their finishing times affected by air pollution levels on race days in recent years.

Researchers at the University of Leicester analysed more than 2.7 million race performances from some of the most popular World Marathon Majors, which host thousands of athletes every year, across editions held between 2010 and 2024.

“From our analysis of more than two million marathon runners, we observed that levels of nitrogen dioxide were strongly associated with their finishing time,” said James Donaldson, the study’s lead author.

For every microgram-per-cubic-metre (µg/m3) increase in nitrogen dioxide, finishing times were 1.43 minutes slower for men and 1.56 minutes slower for women, the researchers found.

On a high-pollution race day when nitrogen dioxide levels reached 10.3 µg/m³ compared with a low-pollution level of 5.2 µg/m³, finishing times were around seven to eight minutes longer.

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