Air Pollution Can Undermine the Health Benefits of Exercise

Most of us don’t notice it, but every time we step outside we may be exposed to varying levels of air pollution. When polluted air is inhaled, tiny particles can penetrate deep into the lungs, damaging lung tissue and increasing the risk of respiratory disease and cancer.

“Under certain conditions, air pollution can reach levels where avoiding outdoor physical activity may be the healthier choice. This can also occur in Denmark during specific pollution episodes,” says Adelina Rogowska-Wrzesinska, research leader at the Department of Biochemistry and Molecular Biology and the SDU representative in the EU-funded research project MARKOPOLO. The MARKOPOLO project investigates how particle and noise pollution affect the brain and the heart.

As part of their work, Rogowska-Wrzesinska and her colleagues have followed a major international study recently published in The Lancet Regional Health – Western Pacific.

A study of 500.000 people

The study tracked half a million Chinese adults and examined how outdoor physical activity influences the risk of hospitalization for chronic obstructive pulmonary disease (COPD) under different levels of air pollution.

“What makes this study so striking is that it challenges the idea that exercise is always healthy. In highly polluted environments, the health benefits of outdoor physical activity can be substantially reduced and, in some cases, may even reverse” she says,“in highly polluted environments, being physically active outdoors can actually be harmful.”

The study results are described in the scientific article Effect modification of long-term air pollution exposure on the association of physical activity with COPD hospitalization: a prospective cohort study of 0.5 million Chinese adults and can be found here. 

Also a problem in Europe

Although the study was conducted in China, its findings are highly relevant for Europe as well.

“Air pollution is a global public health issue, and findings from large international studies are relevant far beyond the region in which they are conducted,” Rogowska-Wrzesinska emphasizes. “Many Europeans are exposed to unhealthy air, and that exposure can undermine their health over time.”

At first glance, it might seem obvious that air pollution is mainly a big-city problem—and that urban residents should therefore avoid outdoor exercise. But the reality is far more complex. Air pollution can occur on a very local scale and vary greatly from place to place, explains Adelina Rogowska-Wrzesinska:

“We tend to think of air pollution as something that happens along busy roads or in city centers,” she explains. “But particles can accumulate or be redirected by buildings, trees, or parks. Pollution levels can change dramatically within just a few hundred meters.”

Farmers and road workers at risk

Adelina Rogowska-Wrzesinska therefore recommends that Danish health authorities make greater efforts to identify and issue warnings about local occurrences of air pollution.

“People who work in agriculture and frequently spend time near petrol- and diesel-powered vehicles and machinery, as well as dust-generating agricultural activities, are also in a risk group. The same applies to road workers. Around these people, ultra-local air pollution can develop,” she says.

In her view, this leads to a major dilemma: Is it still healthy to exercise outdoors when there may be air pollution, or should one, on certain occasions, refrain from doing so?

Higher Risk of COPD

In the Chinese study, researchers found that physical activity among adults living in areas with low air pollution was generally associated with a lower risk of hospitalization for COPD. However, in areas with high pollution levels, this benefit was either weakened or entirely absent. In some cases, there was even a tendency for high levels of physical activity to increase the risk of hospitalization for COPD when pollution levels were very high.

"This suggests that exposure to very high levels of air pollution can reduce—or possibly offset—the positive health effects that exercise would otherwise provide." 

When people are physically active or exercising, they inhale much larger volumes of air into their lungs. This supplies oxygen to the lungs, increases lung volume, and generally boosts the circulation of oxygen throughout the body.

“This raises an important question about when and where outdoor exercise is most appropriate", Rogowska-Wrzesinska concludes.

The MARKOPOLO project is a four-year, EU-funded research collaboration involving scientists from ten countries, including three researchers from the University of Southern Denmark. More information on the project homepage here.