Air pollution can negate the brain benefits of exercise

Train in polluted air and you risk missing out on some of the brain benefits of exercise, according to two new large-scale 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 ran and rolled vigorously had larger brain volumes and lower dementia risks than their peers. less active. But if people exercised in areas with even moderate air pollution levels, the brain improvements expected from exercise almost disappeared.

The new studies raise questions about how to balance the undeniable health benefits of working out with the downsides of breathing stale air, and point out that our environment can change what exercise does — and doesn’t do. – for our body.

The better the air quality around you while you exercise, the better the workout for your brain.

A large body of evidence shows that, overall, exercise pumps up our brains. In studies, active people generally have more gray matter in many parts of their brains than sedentary people. Gray matter is made up of neurons essential to the functioning of the brain. Fit people also tend to have healthier white matter, which is the cells that support and connect neurons. The white matter often frays with age, shrinking and developing Swiss cheese-like lesions, even in healthy adults. But the white matter of fit people has fewer and smaller lesions.

Partly because of these brain changes, exercise is strongly linked to lower risks of dementia and other memory problems with age.

But air pollution has opposite effects on the brain. In a 2013 study, for example, older Americans living in areas with high levels of air pollution showed scruffy white matter on brain scans and tended to develop higher rates of mental decline than people. older people living elsewhere. And in a 2021 study of rats housed in cages placed near a busy, exhaust-choked highway tunnel in California, most of those bred with a predisposition to a rodent analog of the disease Alzheimer’s quickly developed dementia. But so did another group of rats with no genetic inclination to the disease.

Few studies, however, had explored how exercise and air pollution might interact inside our skulls and whether exercising in polluted air would protect our brains from harmful fumes or compromise the good we otherwise withdraw from the exercise.

People who exercised in even moderately polluted air did not show the kinds of brain improvements linked to a lower risk of dementia. Photography: Keith E. Morrison/New York Times

So for the first of the new studies, published in January in Neurology, researchers from the University of Arizona and the University of Southern California extracted the records of 8,600 middle-aged adults enrolled in the UK Biobank. A wealth of health and lifestyle information, the biobank contains information on over 500,000 UK adults, such as their age, where they live, their socio-economic status, their genomes and a wealth of data on health. Some of the participants also had brain scans and wore activity monitors for a week to track their exercise habits.

The researchers focused on those who wore a monitor, had a brain scan and, according to their trackers, often exercised vigorously, such as running, which meant they breathed heavily during workouts. The harder you breathe, the more air pollutants you breathe in. The researchers also included people who had never worked out vigorously, for comparison.

Using established air quality models, they then estimated air pollution levels where people lived and, finally, compared each other’s brain scans.

As expected, vigorous exercise was generally linked to strong brain health. Men and women who presumably lived and worked in low-polluted areas had relatively large amounts of gray matter and a low incidence of white matter damage, compared to people who had never exercised vigorously. And the more they exercised, the better their brains tended to look.

But all of the beneficial associations nearly disappeared when users lived in areas with even moderate air pollution. (Levels in this study were mostly within ranges considered acceptable for health by European and US air quality standards.) Their gray matter volume was smaller and white matter lesions were more numerous. than in people living and exercising away from pollution, even though their workouts were similar.

Extending these results in a second follow-up study published this month in Medicine & Science in Sports & Exercise, the same scientists repeated aspects of this experiment with 35,562 other older participants in the UK Biobank, comparing the habits of people’s exercise, local pollution levels and dementia diagnoses, if any. The data showed that the more people exercised, the less likely they were to develop dementia over time, provided their local air was clear. When it was moderately polluted, however, they were at increased risk of long-term dementia whether they exercised or not.

“These data are of significant importance to our understanding of modifiable risk factors for brain aging,” said Pamela Lein, professor of neurotoxicity at the University of California, Davis, who led the previous study in rats and Pollution. She was not involved in the new studies. “The observation that air pollution negates the well-established beneficial effects of exercise on brain health is alarming and increases the urgency to develop more effective regulatory policies” related to the quality of the air.

Studies have limitations. They are observational and show links between exercise, pollution and brain health, but cannot prove that bad air directly counteracts the brain benefits of exercise, or how this might happen. They also didn’t investigate where people were training, only that some lived in uncertain-looking places.

If your only opportunity to exercise is with pollution in the air, put on a mask and go.  Photography: iStock

If your only opportunity to exercise is with pollution in the air, put on a mask and go. Photography: iStock

But the results suggest that air quality influences training outcomes and that, for the sake of our brains, we should try not to exercise in bad air, said David Raichlen, professor of biological sciences at the University of Southern California. and co-author of the new studies.

Experts say a number of steps can help boost the brain benefits of exercise:

– “Stay away from busy highways, if possible,” said Dr. Raichlen. Automobile exhaust is one of the worst pollutants to human health.

– Training indoors may not be better. “Available evidence suggests that indoor pollution levels are about the same as outdoors,” Dr Raichlen said, unless a building, such as a gym, has installed extensive air filtration systems. Pollutants can easily enter buildings through open doors or windows or through cracks in the structure.

– Masking might help. Both surgical and N95 masks filter out some unhealthy particles, such as soot and other matter, said Melissa Furlong, an environmental epidemiologist at the University of Arizona and co-author of the two studies. “If you don’t mind wearing a mask while exercising,” she said, “it would likely lead to reduced particulate exposure.”

– Most importantly, keep exercising. Exercise has multiple cardiovascular health benefits, and “we don’t want to discourage people from being physically active,” Dr. Raichlan said, even if the air conditions aren’t ideal. In the new studies, the brains of people who exercised in polluted air didn’t look any better, he pointed out, but their brains also didn’t look any worse than those of men. people who did not exercise at all.

So if your only opportunity to exercise is with pollution in the air, put on a mask and go. Then check your local forecast to look for clearer conditions in the future. The better the air quality around you while you exercise, Dr. Raichlen said, the better the workout for your brain. – This article originally appeared in The New York Times.

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