Rizwan Kalani, MD
Particulate air pollution has been associated with stroke and cognitive impairment. In this study, Wilker et al. evaluated the association between fine particulate matter (PM2.5) exposure and residential proximity to major roads with brain structure on MRI – total cerebral brain volume (TCBV), hippocampal volume (HV), white matter hyperintensity volume (WMHV), and silent brain infarcts (SBI).
This was done as part of the Framingham Offspring Study. Nine hundred forty-three community dwellers from New England ≥60 years of age, without a history of stroke or dementia, evaluated between 1998-2001 (which included a brain MRI) were included. PM2.5 were predicted by using satellite-derived measurements and participant home distance to major roadways (United States A1, A2, or A3 highways) were calculated. Volumetric brain MRI measurements of TCBV (ratio of brain parenchymal volume to total cranial volume), HV, WMH (based on ratio of WMHV volume / total cranial volume), extensive (E-WMHV: >1 standard deviation above mean), and SBI (based on size and location) were determined. Vascular risk factors and education history, as well as blood pressure measurements and fasting plasma homocysteine levels were obtained from patients during clinical evaluation.
Higher PM2.5 was associated with smaller TCBV and higher odds of SBI; no association was demonstrated with HV, WMHV, or E-WMHV. A 2µg/m3 increase in PM2.5 was associated with an average -0.32% change in TCBV (95% CI -0.59 to -0.05); higher PM2.5 conferred a 1.46 times (95% CI 1.10-1.94) higher odds of SBI. An IQR difference in subject residence distance to a major road (173 meters) was associated with 0.10 higher WMHV (95% CI 0.01-0.19). Proximity to a major road was not associated with E-WMHV, TCBV, HV, or SBI. Sex, diabetes, obesity, tobacco exposure, or income (below 25th percentile) did not have an effect on the associations seen.
This report provides additional evidence that long-term environmental air pollution exposure is associated with structural brain changes – atrophy and small vessel cerebrovascular disease – that are linked with cognitive and functional impairment in older adults. Major limitations of this manuscript include the possibility of additional confounding variables that may impact results and evaluation of a relatively homogenous population from New England (which may limit generalizability of findings). Future work will have to include elucidating mechanisms by which ambient air pollutants cause the structural brain alterations observed as well the assessment of their impact in regions with high long-term pollution exposure.