Research shows physical activity offers significant health benefits for the brain.

But a new paper in the journal Neurology reveals air pollution might cut into those gains.

"If you are capable of exercising away from those areas, I would encourage you to do so. If you're a policymaker, it would be great to just think about some of the larger effects of policies around air pollution," said lead author Melissa Furlong of the Department of Community, Environment and Policy in UA's College of Public Health.

A study of 8,600 participants in the UK Biobank database who exercised during periods of varying air pollution links physical activity to improvements in gray matter.

Furlong said it also lowers white matter hyperintensity, a marker for brain lesions linked to stroke and neurodegenerative diseases.

"The higher your load of white matter hyperintensity, the higher risk you have for dementia and other kinds of brain diseases," she said. 

Air pollution, especially nitrogen dioxide and 2.5-micron particles, correlated with lower gray matter volumes.