Science

Melissa A. Furlong, Gene E. Alexander, Yann C. Klimentidis, David A. Raichlen

Objective: In high pollution areas, physical activity may have a paradoxical effect on brain health by increasing particulate deposition in the lungs. We examined whether physical activity modifies associations of air pollution with brain volumes in an epidemiological framework.

Methods: The UK Biobank (UKB) enrolled >500,000 adult participants from 2006-2010. Wrist accelerometers, multimodal MRI with T1 images and T2 FLAIR data, and land use regression, were used to estimate vigorous physical activity (VigPA), structural brain volumes, and air pollution (AP) respectively in subsets of the full sample. We evaluated associations between AP interquartile ranges, VigPA, and brain structure volumes, and assessed interactions between AP and VigPA.

Results: 8,600 participants were included, with an average age of 55.55 (sd=7.46). After correcting for multiple testing, in overall models VigPA was positively associated with grey matter (GMV) and negatively associated with white matter hyperintensity volumes (WMHV), while NO2, PM2.5absorbance, and PM2.5 were negatively associated with GMV. NO2 and PM2.5absorbance interacted with VigPA on WMHV (FDR-corrected interaction p-values=0.037). Associations between these air pollutants and WMHVs were stronger among participants with high VigPA. Similarly, VigPA was negatively associated with WMHV for those in areas of low NO2 and PM2.5absorbance, but was null among those living in areas of high NO2 and PM2.5absorbance.

Conclusions: Physical activity is associated with beneficial brain outcomes, while AP is associated with detrimental brain outcomes. Vigorous physical activity may exacerbate associations of AP with white matter hyperintensity lesions, and AP may attenuate the beneficial associations of physical activity with these lesions.