Effects of Traffic-Related Air Pollution on Cognitive Function, Dementia Risk and Brain MRI Findings in the Cardiovascular Health Study

Abstract

Consistent and compelling links between long-term air pollutant exposure and respiratory and cardiovascular disease have been established. Far less is known regarding the impact of air pollution on the brain. Using residence-specific estimates of long-term air pollutant exposure based on regulatory monitors, we investigated the effects of particulate matter < 10 μm in diameter (PM<super>10</super>) and nitrogen dioxide (NO<super>2</super>) on cognitive decline, dementia risk and brain MRI-detected findings in the Cardiovascular Health Study (CHS), a large cohort of older adults residing in three communities in the U.S. Both pollutants were associated with significantly steeper cognitive decline, assessed by the Modified Mini-Mental State Examination and the Digit Symbol Substitution Test in linear regression analyses with generalized estimating equations. In logistic and Cox regression analyses, neither air pollutant was linked significantly to higher risk of prevalent or incident dementia or Alzheimer's disease. However, a 10 μg/m<super>3</super> elevation in estimated long-term PM<super>10</super> exposure was associated with 2.45-fold increase in odds of prevalent vascular dementia (95% CI: 1.23, 4.86). The same elevation in PM<super>10</super> exposure was associated with a 0.14-unit worse white matter grade (95% CI: 0.01, 0.27), and a 10 ppb increase in NO<super>2</super> exposure was associated with a 0.37-unit worse white matter grade (95% CI: 0.14, 0.61). Worsening white matter between MRIs and MRI-detected infarcts were not significantly associated with PM<super>10</super> or NO<super>2</super> exposure. In summary, we found significant associations between estimated long-term exposure to air pollutants and faster rates of cognitive decline, elevated risk of vascular dementia (VaD) and higher white matter grade on brain MRI. Our findings add to the existing strong rationale for limiting exposure to air pollutants.