The research team examined 2,756,553 net finishing times from marathons held in Berlin, Boston, Chicago, London, New York City and Tokyo between 2010 and 2024. By combining this vast performance dataset with race-day measurements of air pollutants at each event, the researchers were able to test whether short-term exposure to urban air pollution left a measurable imprint on human endurance. The study, led by Dr James Donaldson, Postdoctoral Researcher in Health and the Environment at the University of Leicester, and involving investigators including Professor Andre Ng, Dr Samuel Cai and Professor Anna Hansell, was published in Sports Medicine Open in September 2026 and was supported by the National Institute for Health and Care Research Biomedical Research Centre Leicester.

The headline finding concerns nitrogen dioxide, a pollutant generated mainly by road traffic and combustion processes. According to Dr Donaldson, each additional microgram per cubic metre of nitrogen dioxide was associated with a finishing time 1.43 minutes slower in men and 1.56 minutes slower in women. In the context of a marathon, where elite competitors are separated by seconds and where personal bests are often chased for years, a slowdown of more than a minute per microgram per cubic metre represents a substantial effect, particularly given that pollution levels across the studied races were generally only low to moderate by global standards.

The pattern of vulnerability within the field of runners was striking. The negative effects of nitrogen dioxide were approximately six times larger for recreational runners than for elite athletes, and younger runners aged 18 to 29 showed larger effects than older participants. This gradient suggests that the performance cost of polluted air is not distributed evenly across the field, but instead concentrates among the mass of amateur runners who make up the overwhelming majority of participants in the World Marathon Majors and who often spend four, five or more hours on the course.

Dr Donaldson offered several potential explanations for these patterns. Slower runners remain on the marathon course for longer, meaning they accumulate a greater dose of pollutants over the duration of the race. In addition, the physiological adaptations produced by the high-intensity training undertaken by elite athletes may confer some protection against the harmful effects of air pollution on performance. Recreational runners, who typically have less training behind them, may find that the added physiological strain imposed by pollution during a marathon has a comparatively greater effect on their result.

Notably, the study did not find a statistically significant relationship between fine particulate matter, known as PM2.5, and marathon finishing times. Fine particulate matter consists of tiny airborne particles generated by vehicle emissions, industry, heating and other combustion-related sources, and both nitrogen dioxide and particulate pollution have been linked to adverse health effects, particularly on the heart and lungs. The absence of a significant particulate-matter signal in this dataset may reflect the relatively low and narrow range of PM2.5 concentrations observed on race days, which limits the ability of statistical models to detect an effect even if one exists at higher exposures.

An important contextual point is that race-day concentrations of nitrogen dioxide and PM2.5 in this sample were generally low to moderate relative to the 2021 World Health Organization air quality guideline levels, with most of the marathons falling near or below those thresholds. That effects of this size emerged at such modest concentrations carries implications well beyond elite sport. It suggests that even air quality considered acceptable by international standards may measurably constrain human physical performance during prolonged maximal exertion, when ventilation rates rise dramatically and large volumes of air are drawn deep into the lungs.

Professor Bryan Williams, Chief Scientific and Medical Officer at the British Heart Foundation, which supported the study, cautioned that the research is observational and cannot prove cause and effect, while noting that the result is unsurprising given what is known about the biological effects of polluted air. Breathing polluted air can trigger inflammation, damage blood vessels and affect breathing, all of which could plausibly impair endurance performance. He also highlighted a positive trend: levels of nitrogen dioxide and PM2.5 on marathon day in London appear to have fallen substantially since the 2010 event, news he described as welcome for heart health, and he emphasised that exercise itself remains highly beneficial, capable of reducing the risk of heart and circulatory diseases by up to 35 per cent. The findings, he stressed, should not put people off running.

From a practical standpoint, the Leicester researchers argue that air quality and event-related traffic policies should now be considered alongside temperature and humidity when cities plan urban endurance events and when runners are advised about race preparation. Large marathons already close roads and reroute traffic; the new evidence suggests such measures may do more than manage congestion, potentially influencing the times recorded by hundreds of thousands of amateur participants. Race organisers might also weigh start times, course design and real-time air quality forecasts when scheduling and managing mass-participation events in dense urban environments.

The implications extend past the marathon finish line to anyone exercising outdoors in a city, from commuters cycling to work to children playing sport in traffic-exposed neighbourhoods. Recognising this broader relevance, researchers at the University of Leicester are developing the P-STEP app, the Personalised Space Technology Exercise Platform, with support from the European Space Agency. The app uses real-time, location-specific air quality information to help people decide when and where to exercise outdoors while minimising their exposure to pollution. Work of this kind sits within the British Heart Foundation Leicester Centre of Research Excellence, led by Director Professor André Ng, which unites discovery science, clinical intervention and population health research, and within the NIHR Biomedical Research Centre Leicester, hosted by the University Hospitals of Leicester NHS Trust in partnership with the University of Leicester, Loughborough University and University Hospitals of Northamptonshire NHS Group. Together, the study and the tools emerging from it point toward a future in which air quality data becomes a routine part of athletic planning, much as weather forecasts already are, and in which the invisible chemistry of city air is recognised as a genuine factor in human performance.

Subject of Research: The association between race-day air pollution exposure and marathon running performance across the six World Marathon Majors

Article Title: Higher pollution levels linked to slower marathon times across six world marathon majors

Article References: Higher pollution levels linked to slower marathon times across six world marathon majors. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: air pollution, nitrogen dioxide, PM2.5, marathon, World Marathon Majors, exercise performance, University of Leicester, recreational runners, public health, urban air quality, cardiovascular health, endurance sport