Higher levels of air pollution on marathon race days are associated with slower finishing times, with recreational runners appearing to be affected more than elite athletes, new research suggests.
We recently reported on a study that took place during this year’s London Marathon and now, researchers at the University of Leicester have gone global, analysing more than 2.7 million marathon performances from six of the world’s major races between 2010 and 2024.
The study examined 2,756,553 finishing times from the Berlin, Boston, Chicago, London, New York City and Tokyo marathons, alongside levels of air pollution recorded on race days.
The researchers found that for every increase of 1 μg/m³ of NO2, finishing times were around 1.43 minutes slower for men and 1.56 minutes slower for women.
The effect was substantially larger among recreational runners, with the researchers estimating that the impact of nitrogen dioxide was around six times greater than among elite athletes.
Younger runners, aged 18 to 29, also appeared to experience a greater effect than older participants.
Nitrogen dioxide is produced largely by road traffic and combustion, while fine particulate matter, known as PM₂.₅, can come from vehicle emissions, industry, heating and other sources.
The study, published in Sports Medicine Open, found that levels of PM₂.₅ were not significantly associated with marathon finishing times.
Dr James Donaldson, a postdoctoral researcher in health and the environment at the University of Leicester and lead author of the study, said: ‘There are many potential explanations for these patterns. Firstly, slower runners remain on the marathon course for longer, so they may accumulate greater pollutant dose during race day. Secondly, the physiological adaptations that result from the high-intensity training undertaken by elite athletes may offer some protection against the harmful effects of air pollution.
‘Recreational runners may have less training behind them, so the added strain of pollution during a marathon could have a greater effect on their performance.’
The researchers noted that pollution levels recorded during the marathons studied were generally low to moderate compared with the World Health Organization’s 2021 air quality guidelines.
The study was observational, meaning it can identify an association between pollution and performance but cannot establish that air pollution directly caused runners to record slower times.
Professor Bryan Williams, chief scientific and medical officer at the British Heart Foundation, which supported the research, said: ‘Despite the known harms of air pollution, it is important to note that levels of nitrogen dioxide and PM2.5 on marathon day in London appear to have fallen substantially since the 2010 event, which a great news for heart health. As well as this, the fact remains that exercise is still very beneficial for your cardiovascular health – it can reduce the risk of heart and circulatory diseases by up to 35%. While interesting, the findings of this study definitely shouldn’t put people off running.’
The University of Leicester is also developing an app that uses real-time, location-specific air quality information to help people choose when and where to exercise outdoors while reducing exposure to pollution.
The full research can be read here.
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