Train in polluted air and you may miss 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, involving tens of thousands of British men and women, found that more often than not, people who ran and cycled vigorously had higher brain volume and lower risks of dementia than their less active peers. But if people exercised in areas with moderate levels of air pollution, the expected brain improvements from exercise all but disappeared.
The new studies raise questions about how to balance the undeniable health benefits of exercise with the downsides of breathing stale air, and underscore that our environment can change what exercise does and doesn’t do for our bodies.
A large body of evidence shows that, in general, exercise strengthens our brains. In studies, active people usually play sports more gray matter in many parts of their brains than sedentary people. Gray matter is made up of the essential neurons that function in the brain. Fit people also tend to have healthier white matter, that is, the cells that support and connect neurons. The white matter often frays with age, shrinks, and develops Swiss cheese-like lesions even in healthy adults. But the white matter of fit people shows fewer and smaller lesions.
Partly as a consequence 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 studyFor example, older Americans who lived 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 older people who lived elsewhere. and in a 2021 study of rats housed in cages. placed near an exhaust-clogged and heavily trafficked highway tunnel in Northern California, most of those raised with a predisposition to a rodent-like Alzheimer’s disease soon developed dementia. But so did another group of rats with no genetic predisposition 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 gases or undermine the good we get from exercising.
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 obtained records from 8,600 middle-aged adults enrolled in the UK Biobank. A vast trove of health and lifestyle records, the Biobank contains information on more than 500,000 British adults, including their ages, locations of residence, socioeconomic status, genomes and extensive health data. Some of the participants also completed brain scans and wore activity monitors for a week to track their exercise habits.
The researchers focused on those who had worn a monitor, had a brain scan and, according to their trackers, often engaged in vigorous exercise, such as running, which meant they were breathing heavily during workouts. The more you breathe, the more air pollutants you attract. The researchers also included some people who never exercised vigorously for comparison.
Using established models of air quality, they then estimated the levels of air pollution where people lived, and finally compared everyone’s brain scans.
Benefits that disappear
Unsurprisingly, vigorous exercise was generally associated with strong brain health. Men and women who lived and presumably exercised in areas with little air pollution had relatively large amounts of gray matter and a low incidence of white matter lesions, compared with people who never exercised vigorously. And the more they exercised, the better their brains tended to look.
But any beneficial association almost disappeared when the athletes lived in areas with even moderate air pollution. (The levels in this study were mostly within limits considered acceptable for health under European and US air quality standards.) Similary.
Extending these findings 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 from the UK Biobank, comparing people’s exercise habits, 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, as long as the air in their locality was clear. However, when it was moderately polluted, they had a higher risk of long-term dementia, whether they exercised or not.
‘Alarming’ finding
“These data are of great importance 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 earlier study on 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 heightens the urgency to develop more effective regulatory policies” related to air quality.
The 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 exercised, just that some lived in dodgy-looking places.
But the results suggest that air quality influences training outcomes and that, for our brain’s sake, we should try not to exercise in stale air, said David Raichlen, a USC professor of biological sciences and a co-author. author of the new studies.
Boost brain health
In practice, a number of measures can help reinforce the benefits of exercise for the brain, experts say.
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“Stay off busy roads, if possible,” Dr. Raichlen said. Automobile exhaust gases are among the worst pollutants for human health.
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Check local conditions at airnow.gov, which uses the color-coded Air Quality Index to rate air quality by zip code. Most weather apps also include the local AQI. Aim to train with air quality rated Green, which is Good. Air quality changes throughout the day, so check back in a few hours if conditions seem unfavorable at first.
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Exercising 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 extensive air filtration systems installed. Contaminants can easily enter buildings through open doors or windows or cracks in the structure, and the government does not routinely monitor indoor air quality. You can learn more in Environmental Protection Agency website.
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Masking might help. Both surgical and N95 masks filter out some harmful particles, such as soot and other matter, said Melissa Furlong, an environmental epidemiologist at the University of Arizona and a co-author of the two studies. “If you don’t mind wearing a mask while exercising,” she said, “this will likely result in reduced particulate exposure.”
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Most importantly, keep exercising. Exercise has multiple benefits for cardiovascular health, 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 weren’t any worse than those of people who didn’t exercise at all, either.
So if your only chance to exercise is with some pollution floating in the air, put on a mask and go. Then check your local AQI 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 exercise is for your brain.
