Exercising in Polluted Air May Dampen the Brain Benefits of Exercise

January 3, 2022

Like to jog, cycle or play sports outdoors? It is good for your brain. But for optimal brain health, you may want to stick to parks or paths that are removed from traffic and other sources of polluted air.

Numerous studies show that regular exercise is good for the brain, and that people who exercise regularly in their younger years are at lower risk of developing Alzheimer’s disease in old age. But a new study found that people who do vigorous physical activities in areas with higher air pollution had fewer of the brain benefits from exercise.

“Prior studies have shown adverse effects of air pollution on the brain,” said study author Melissa Furlong of the University of Arizona in Tucson, and “vigorous exercise may increase exposure to air pollution,” since we do breathe in more air when we exercise and therefore more pollutants.

“We did show that physical activity is associated with improved markers of brain health in areas with lower air pollution,” Dr. Furlong said. “However, some beneficial effects essentially disappeared for vigorous physical activity in areas with the highest levels of air pollution.”

“We found that, while vigorous physical activity was good for brain health, exposure to air pollution seemed to mute some of these benefits,” said David Raichlen, the study’s senior author and a professor of human and evolutionary biology at the USC Dornsife College of Letters, Arts and Sciences. “For example, vigorous physical activity reduced white matter lesions, a key marker of brain health, but these benefits were eliminated in areas with high air pollution.

“We’re not recommending we avoid all exercise in air pollution,” Dr. Raichlen said. “But, since increased white matter lesions are a risk for stroke and Alzheimer’s disease, we do think we should put more thought into where we exercise, and, for example, avoid areas that are close to vehicle traffic.”

 Dr. Furlong likewise emphasized that polluted air should not deter anyone from exercising, since the benefits of exercise far outweigh any downsides from breathing in air pollutants. “Overall, the effect of air pollution on brain health was modest — roughly equivalent to half the effect of one year of aging, while the effects of vigorous activity on brain health were much larger — approximately equivalent to being three years younger.”

For the study, the researchers looked at two brain changes that may be indicators of brain health: white matter hyperintensities, which are a sign of injury to the brain’s white matter; and gray matter volume. People who have more white matter hyperintensities and/or diminished gray matter volume are at higher risk of developing Alzheimer’s disease or other forms of dementia.

The researchers looked at 8,600 men and women in Britain, average age 56, who were part of a large medical database. They equipped the study participants with fitness trackers to gather information on much exercise they tended to get in an average week. Based on where they lived, they also had information on how much air pollution they were typically exposed to when they exercised, considering such factors as exposure to traffic exhaust or industrial smoke.

The researchers found that people who tended to get at least 30 minutes of vigorous physical activity each week had greater gray matter brain volumes than their peers who got no vigorous exercise. The difference was subtle but significant.

People who got regular vigorous exercise also tended to have fewer white matter intensities that their sedentary peers. But the researchers found that vigorous physical activity reduced white matter hyperintensities only in people who worked out in areas with low levels of air pollution, and not in those who exercised in highly polluted areas. The findings were published in the scientific journal Neurology.

“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,” Dr. Furlong said. “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.”

Living for years in areas high in smog and other air pollutants may contribute to brain deterioration, and possibly increase the risk of developing Alzheimer’s disease, a growing body of evidence shows. Other research suggests that even in the short term, breathing in air pollutants may lead to declines in memory and thinking skills.

Earlier studies have also shown that living in areas with heavily polluted air, whether from car emissions, power plants, factories or forest fires, can accelerate the onset of Alzheimer’s in people who may already be vulnerable to developing the disease. People who live in polluted areas also tend to have higher levels of the telltale brain amyloid plaques tied to Alzheimer’s disease.

It is difficult to establish a direct link between environmental toxins and a disease like Alzheimer’s, because so many factors are involved over very long periods of time, the exposure level to pollutants over the years can be difficult to evaluate and variable, and there are many risk factors for Alzheimer’s disease, including hearing loss, high blood pressure, obesity, depression, lack of social contact and being sedentary. But anything we can do to help minimize risk may have a sizable impact years down the road.

By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Marc Flajolet, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.

Source: Melissa A. Furlong, PhD; Gene E. Alexander, PhD; Yann C. Klimentidis, PhD; David A. Raichlen, PhD: “Association of Air Pollution and Physical Activity With Brain Volumes.” Neurology, December 8, 2021


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