Should We Exercise When Air Pollution Is High?

Is it safe to exercise in polluted air? Discover how physical activity and air pollution interact, and what the latest science recommends to stay healthy.

[This text was written jointly by Alícia Josa, predoctoral researcher at ISGlobal, Ioar Rivas, Associated Researcher at ISGlobal, and Sarah Koch, Associated Researcher at ISGlobal.]

Physical activity improves health. But in polluted environments, could it actually do more harm than good? When we engage in physical activity, our breathing rate increases. This means we inhale more air and, with it, more air pollutants. Therefore, in polluted environments, practicing physical activity could worsen the effects of air pollution on our health. Given that 99% of the world population lives in areas where air pollution levels exceed the World Health Organization (WHO) guidelines, understanding how physical activity in polluted environments affects our health is paramount.

Measuring the combined effects of exercise and air pollution on health

In the past, research has examined physical activity and air pollution as separate factors. In recent years, a more integrated measure has been emerging: the inhaled dose of air pollution (IDoAP). This parameter is a measure of the exposure to air pollutants that also accounts for current activity levels. It factors in the rate and volume of breathing, and therefore captures the amount of air pollutants that enter the respiratory tract. Expressed in mathematical terms, the IDoAP is estimated as the product of the minute ventilation (how much air we breathe per minute), the air pollutant concentration, and the exposure duration.

The inhaled dose of air pollution (IDoAP) is a measure that captures the amount of air pollutants that enter the respiratory tract

Estimating the health effects in dependence of the IDoAP might help us address the question of whether the benefits of physical activity outweigh the risks of air pollution exposure. To summarise the current evidence on the health effects of IDoAP, we conducted a systematic review that was published in the European Respiratory Review.

What is the inhaled dose of air pollution and how does it affect us?

The review included 25 original-research studies in which participants performed different types of physical activity such as walking or cycling while they were exposed to different types of air pollutants. They included both field and laboratory studies, and mainly measured ozone (O₃) and particulate matter < 2.5 µm (PM_2.5). Ozone is a secondary pollutant formed in the atmosphere from precursors such as nitrogen oxides (NOₓ) and volatile organic compounds (VOCs) in the presence of sunlight. PM_2.5 in turn are tiny particles that can be emitted by several sources, like traffic, factories, wildfires, and even cooking.

It appears that healthy adults should adhere to their physical activity routines, also at higher intensities, while trying to avoid times and areas with peak air pollutant concentrations. This includes morning peak hours and streets with high-intensity traffic. These measures should be accompanied by initiatives that reduce air pollution levels

We found that a greater IDoAP of ozone was associated with an immediate reduction in lung function. Notably, this effect was driven by the concentration of ozone rather than minute ventilation. This means that reducing the IDoAP by lowering the intensity of physical activity and thus reducing the amount of air that we inhale does not appear to be a strategy to reduce the harmful effects of air pollution. Rather, it appears that healthy adults should adhere to their physical activity routines, also at higher intensities, while trying to avoid times and areas with peak air pollutant concentrations. This includes morning peak hours and streets with high-intensity traffic. These measures should be accompanied by initiatives that reduce air pollution levels.

Who’s Missing from the Research on Air Pollution and Physical Activity?

The review also highlighted some gaps in the current research. Most studies focused on healthy adults, while vulnerable or susceptible populations were largely overlooked. This means populations that are more likely to be exposed to air pollution or to suffer the harmful effects of air pollution have not been sufficiently studied yet. This includes:

• Individuals with pre-existing conditions
• Children and adolescents
• Pregnant individuals
• People with significant occupational exposures
• People from low- and middle-income regions

Also, most studies focused on the effects of IDoAP of ozone and particulate matter on lung function. We need further research to understand the effect of IDoAP of other air pollutants, like nitrogen dioxide or black carbon, which are very relevant traffic-related air pollutants and thus of particular relevance in cities or areas where traffic is dense and congestions a daily occurrence. We also need more research on other health outcomes, such as the cardiovascular, cognitive and mental health, to see if IDoAP has different effects on these outcomes.

As research advances, understanding IDoAP could help us maximize the benefits of physical activity, even in polluted areas, while pushing for cleaner air worldwide.