Study: Air Pollution Potentially Reduces Benefits of Physical Activity On the Brain

Individuals who got the greatest amounts of vigorous exercise each week had more gray matter volume than individuals who did not get any vigorous exercise.

New research suggests that individuals who do vigorous physical activities in areas with higher air pollution may show less benefit from that exercise with certain markers of brain disease.

According to a press release from the American Academy of Neurology, researchers examined markers including white matter hyperintensities, which indicate injury to the brain’s white matter, and gray matter volume. Larger volumes of gray matter and smaller volumes of white matter hyperintensity are signifiers of overall better brain health. However, air pollution could limit the impacts of exercise on these markers of brain health, according to the study.

“Vigorous exercise may increase exposure to air pollution, and prior studies have shown adverse effects of air pollution on the brain,” said study author Melissa Furlong, PhD, in the press release. “We did show that physical activity is associated with improved markers of brain health in areas with lower air pollution. However, some beneficial effects essentially disappeared for vigorous physical activity in areas with the highest levels of air pollution.”

In the study, researchers examined 8600 individuals with an average age of 56 years from the UK Biobank database. Individuals’ exposure to pollution, including nitrogen dioxide and particulate matter, was estimated with land use regression, which models air pollution levels based on air monitors and land use characteristics such as traffic, agriculture, and industrial sources of air pollution.

Participants’ exposure to air pollution was categorized into 4 equal groups, from lowest air pollution to highest, and each individual’s physical activity was measured for 1 week with a wearable movement-detecting device. Researchers then characterized their physical activity patterns depending on how much vigorous physical activity they got, ranging from none to 30 minutes or more per week.

On average, individuals who got the greatest amounts of vigorous physical activity each week had 800 cm3 gray matter volume, compared to an average of 790 cm3 in individuals who did not get any vigorous exercise. Researchers also found that air pollution exposures did not alter the effects of physical activity on gray matter volume.

However, the study found that air pollution exposures altered the impact of vigorous physical activity when looking at white matter hyperintensities. After adjusting for age, sex, and other covariates, researchers found that vigorous physical activity reduced white matter hyperintensities in areas of low air pollution, but these benefits were not found in individuals in high air pollution areas.

“That’s not to say people should avoid exercise,” Furlong said in the press release. “Overall, the effect of air pollution on brain health was modest—roughly equivalent to half the effect of 1 year of aging, while the effects of vigorous activity on brain health were much larger—approximately equivalent to being 3 years younger.”

The study used air pollution values from 1 year only, and levels may vary from year to year, according to the researchers.

“More research is needed, but if our findings are replicated, public policy could be used to address people’s exposure to air pollution during exercise,” Furlong said in the press release. “For example, since a significant amount of air pollution comes from traffic, promoting running or bicycling along paths far from heavy traffic may be more beneficial.”

REFERENCE

Does Air Pollution Reduce the Benefits of Physical Activity on the Brain? News release. American Academy of Neurology; December 8, 2021. Accessed January 19, 2022. https://www.aan.com/PressRoom/Home/PressRelease/4940

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