LOS ANGELES—Where you exercise is just as important for brain health as exercise itself. That’s the conclusion of a study released today by researchers at University of Southern California (USC) and the University of Arizona, which found that vigorous exercise in a highly polluted area can diminish the positive brain benefits of exercise. “We found that, while vigorous physical activity was good for brain health, exposure to air pollution seemed to mute some of these benefits,” USC professor and study co-author David Raichlen said in a statement. “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. 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, …