Source: New York Times
People who worked out in even moderately polluted air did not show the kinds of brain improvements tied to a lower risk of dementia.
The benefits of working out
Work out in polluted air and you may miss out on some of the brain benefits of exercise, according to two, large-scale new studies of 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 rode vigorously had larger brain volumes and lower risks for dementia than their less active peers. But if people exercised in areas with even moderate levels of air pollution, the expected brain improvements from exercise almost disappeared.
In studies, active people generally sport more gray matter in many parts of their brains than sedentary people. Gray matter is made up of the brain’s essential, working neurons. Fit people also tend to have healthier white matter, meaning the cells that support and connect neurons. White matter often frays with age, shrinking and developing Swiss-cheese-like lesions even in healthy adults. But fit people’s white matter shows fewer and smaller lesions. Partially as a consequence of these brain changes, exercise is strongly linked with lower risks for dementia and other memory problems with age.
Air pollution mitigates benefits
But air pollution has the opposite effects on brains. In a 2013 study, for example, older Americans living in areas with high levels of air pollution showed bedraggled white matter on brain scans and tended to develop higher rates of mental decline than older people living elsewhere.
Few studies, though, had explored how exercise and air pollution might interact inside our skulls and whether working out in smoggy air would protect our brains from noxious fumes or undermine the good we otherwise gain from working out.
The researchers focused on those who had worn a monitor, had a brain scan and, according to their trackers, often exercised vigorously, such as by running, which meant they breathed heavily during workouts. The heavier you breathe, the more air pollutants you draw in. The researchers also included some people who never worked out vigorously, for comparison.
As expected, vigorous exercise was linked, in general, to sturdy brain health. Men and women who lived and presumably worked out in areas with little air pollution showed relatively large amounts of gray matter and low incidence of white matter lesions, compared to people who never exercised hard. And the more they exercised, the better their brains tended to look.
But any beneficial associations almost disappeared when exercisers lived in areas with even moderate air pollution. (Levels in this study were mostly within the bounds considered acceptable for health by European and American air quality standards.) Their gray matter volume was smaller and white matter lesions more numerous than among people living and exercising away from pollution, even if their workouts were similar.
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. The data showed 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, though, they had an increased long-term risk of dementia, whether they exercised or not.
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 occur. They also did not look into where people worked out, only that some lived in places with iffy air.
But the results do intimate that the quality of the air influences the results of the workout and that for the sake of our brains, we should try not to exercise in bad air, said David Raichlen, a professor of biological sciences at U.S.C. and co-author of the new studies.
- “Stay away from busy highways, if at all possible,” Dr. Raichlen said. Automobile exhausts are among the worst pollutants for human health.
- Working out indoors may be no better. “The available evidence suggests pollution levels indoors are about the same as those outside,” Dr. Raichlen said, unless a building, such as a gym, has installed extensive air filtration systems. Pollutants can readily enter buildings through open doors or windows or cracks in the structure, and the government doesn’t routinely monitor indoor air quality.
- Masking might help. Both surgical and N95 masks filter some unhealthy particulates, 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, “this would likely result in a reduction of exposure to particulates.”
- Most important, keep exercising. Exercise has multiple benefits for cardiovascular health, and “we do not want to discourage people from being physically active,” Dr. Raichlen said, “even if air conditions are not ideal. In the new studies, the brains of people who exercised in polluted air looked no better, he pointed out — but their brains were also no worse than those of people who did not exercise at all.”
So, if your only opportunity to exercise is with some pollution hanging in the air, don a mask and go. Then check your local A.Q.I. forecast to look for clearer conditions in the future. The better the air quality is around you as you exercise, Dr. Raichlen said, the better the workout will be for your brain.