Ambient Air Pollution Exposure and Cerebral White Matter Hyperintensities in Older Adults: A Cross-Sectional Analysis in the Three-City Montpellier Study

Abstract

Background: Growing epidemiological evidence suggests an adverse relationship between exposure to air pollutants and cognitive health, and this could be related to the effect of air pollution on vascular health.

Objective: We aim to evaluate the association between air pollution exposure and a magnetic resonance imaging (MRI) marker of cerebral vascular burden, white matter hyperintensities (WMH).

Methods: This cross-sectional analysis used data from the French Three-City Montpellier study. Randomly selected participants 65-80 years of age underwent an MRI examination to estimate their total and regional cerebral WMH volumes. Exposure to fine particulate matter (${\mathrm{PM}}_{2.5}$), nitrogen dioxide (${\mathrm{NO}}_2$), and black carbon (BC) at the participants' residential address during the 5 years before the MRI examination was estimated with land use regression models. Multinomial and binomial logistic regression assessed the associations between exposure to each of the three pollutants and categories of total and lobar WMH volumes.

Results: Participants' ($n=582$) median age at MRI was 70.7 years [interquartile range (IQR): 6.1], and 52% ($n=300$) were women. Median exposure to air pollution over the 5 years before MRI acquisition was 24.3 (IQR: 1.7) ${\mu g/m}^3$ for ${\mathrm{PM}}_{2.5}$, 48.9 (14.6) ${\mu g/m}^3$ for ${\mathrm{NO}}_2$, and 2.66 (0.60) ${10}^{-5}/m$ for BC. We found no significant association between exposure to the three air pollutants and total WMH volume. We found that ${\mathrm{PM}}_{2.5}$ exposure was significantly associated with higher risk of temporal lobe WMH burden [odds ratio (OR) for an $\text{IQR increase}=1.82$ (95% confidence interval: 1.41, 2.36) for the second volume tercile, 2.04 (1.59, 2.61) for the third volume tercile, reference: first volume tercile]. Associations for other regional WMH volumes were inconsistent.

Conclusion: In this population-based study in older adults, ${\mathrm{PM}}_{2.5}$ exposure was associated with increased risk of high WMH volume in the temporal lobe, strengthening the evidence on ${\mathrm{PM}}_{2.5}$ adverse effect on the brain. Further studies looking at different markers of cerebrovascular damage are still needed to document the potential vascular effects of air pollution. https://doi.org/10.1289/EHP12231.