Exercising in a polluted place can negate benefits for the brain; understand

Exercising in polluted air could result in losing some of the benefits that exercise provides, according to two major new studies on exercise, air quality and brain health.

The studies, which involved tens of thousands of British men and women, found that most of the time, people who run and cycle vigorously have greater brain volume and face a lower risk of dementia, compared to those who are less active.

But if people exercise in areas where there is air pollution, even at a moderate level, they may not get the brain improvements expected as a result of exercise.

The new studies raise questions about how to balance the undeniable health benefits of exercise and the negative consequences of breathing in poor-quality air, and underscore that our environment can bring about changes in the results that exercise provides — and doesn’t provide — for our bodies.

There are considerable indications that, in general, physical exercise strengthens the brain. In studies, active people in general exhibit more gray matter in many parts of their brains than sedentary people. Gray matter is formed by the essential and functional neurons of the brain.

People who are more fit also tend to have healthier white matter, that is, the cells that support and connect neurons. The white mass often wears away with age, shrinking and developing lesions resembling the holes in Swiss cheese, even in healthy adults. But the white matter of people who are in good shape exhibit fewer injuries, and smaller injuries.

Partly as a result of these brain changes, exercise is strongly correlated with a lower risk of senile dementia and other memory problems as a person ages.
But air pollution has the opposite effect on the brain.

One study reveals, for example, that older Americans who live in areas where air pollution is high show disturbances in the white matter of their brains on CT scans and tend to have higher levels of mental decline than than those of older people living in other areas.

And a study of rats housed in cages placed near a heavy-traffic tunnel that accumulates a large volume of exhaust fumes in Northern California shows that the test subjects did not take long to develop dementia. Most of the animals involved were bred with a predisposition to an animal analogue of Alzheimer’s disease, but the same conclusion applies to another set of mice that are not genetically inclined to the disease.

Few studies, however, have studied how exercise and air pollution might interact inside our skulls, and whether exercising in polluted air would protect our brains from harmful fumes or undermine the benefits that physical activity brings.

So in the first of the new studies, published in January in the journal Neurology, researchers at the University of Arizona and the University of Southern California obtained records from 8,600 middle-aged adults whose data are in the UK Biobank.

The Biobank is a large repository of health and lifestyle information, and holds data on over 500,000 British adults, including their ages, addresses, socioeconomic status, genomes and extensive health records. Some of the participants also underwent brain scans and wore activity monitors for a week to track their exercise habits.

The researchers focused their attention on people who wore monitors, underwent brain scans and, according to the monitoring, exercised vigorously quite often, as evidenced by the rapid pace of breathing during exercise sessions.

The heavier the breath, the more pollutants a person breathes in. The researchers also included, for comparison, data from some people who never exercised vigorously.

Using established models of air quality, they then estimated the levels of pollution in the places where people lived, and finally compared the brain scans of everyone involved.

benefits disappear

As expected, vigorous exercise was generally linked to stronger brain health. Men and women who live and presumably exercise in areas of low air pollution demonstrate a relatively high volume of gray matter and fewer white matter lesions, compared to people who never exercise vigorously. And the more people exercise, the better the condition of their brains appears to be.

But which positive associations practically disappear in the case of people who exercise frequently but live in areas where there is even moderate air pollution. (The levels considered in the study generally fell within acceptable standards for health under current air quality standards in Europe and the United States.)

The gray matter of these people was smaller and the white matter lesions more numerous than those of people who live and exercise far from pollution, even though the exercise regimens were similar.

A follow-up study published this month in the journal Medicine & Sciene in Sports & Exercise amplified these findings. The same scientists repeated aspects of the same work with data from 35,562 older participants registered with the UK Biobank, comparing exercise habits, local pollution levels and diagnoses of senile dementia, if any.

The data showed that the more people exercise, the less likely they are to develop dementia over time — as long as the air in the places where they live is clean. In places where the air was moderately polluted, however, there was an increased risk of long-term dementia, whether the person exercised or not.

“alarming” finding

“These data are significant in terms of our understanding of modifiable risk factors for brain aging,” said Pamela Lein, a professor of neurotoxicity at the University of California, Davis, who led the previous study on rats and air pollution. She did not participate in the new studies.

“The observation that air pollution negates the well-established benefits of physical exercise for brain health is alarming and makes the development of more effective regulatory policies more urgent” on air quality.

The studies have limitations. They are observational and show correlations between exercise, pollution and brain health, but they are not able to prove that poor air quality directly cancels out the benefits of exercise for the brain, or in what way this process could occur. They don’t even consider the places where people exercise, and limit themselves to pointing out that some of them live in places where the air quality is questionable.

But the results suggest that air quality influences the benefits of exercise and that, for the good of our brains, we should try to avoid exercise in places where the air quality is poor, said David Raichlen, a professor of biological sciences at the University. from Southern California and one of the authors of the new studies.

Strengthening brain health

In practice, several measures can help to fortify the benefits of physical exercise for the brain, experts say.

• “Stay away from heavy traffic lanes if possible,” Raichlen said. Car exhausts are one of the most harmful forms of pollution to human health.
• Check local conditions at airnow.gov, which uses a color code to classify air conditions in the United States based on zip codes. Most weather apps also provide information about the local level of air quality. The goal is to exercise in places where the air quality is green, which equates to good. Air quality changes throughout the day; therefore, check back after a few hours if conditions seem unfavorable at first.
• Exercising indoors may not be better. “Available indications are that pollution levels indoors are more or less similar to those prevailing outside,” Raichlen said, unless a building, say a fitness center, has installed extensive air filtration systems. air. Pollutants can easily enter buildings through open doors or windows, or through cracks in the structure, and the government does not regularly monitor indoor air quality. More information is available on the US Environmental Protection Agency (EPA) website.
• Wearing masks can help. Both surgical masks and N95 masks filter out some unhealthy particulates, such as soot and other materials, said Melissa Furlong, an environmental epidemiologist at the University of Arizona and one of the authors of the two studies. “If you don’t mind wearing a mask while exercising,” she said, “the practice is likely to result in a reduction in particulate exposure.”
• The most important thing is to keep exercising. Exercise has multiple cardiovascular health benefits, and “we don’t want to discourage people from being physically active,” Raichlen said, even if the air conditions are suboptimal. In the new studies, the brains of people who exercise in polluted air don’t look any better but they don’t look any worse than those of people who don’t exercise at all, he pointed out.

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So if your only opportunity to exercise is in a place with some air pollution, put on your mask and go. Check forecasts for air quality at the location you are looking for clearer conditions in the future. The better the quality of the air that surrounds you during your workouts, Raichlen said, the better the effect the conditioning session will have on your brain.

Translation by Paulo Migliacci.