Traffic-related air pollution (TRAP) is a major environmental risk
factor with growing evidence linking long-term exposure to adverse brain
morphology outcomes. A direct pathway for pollutant translocation to
the brain via the olfactory bulb has been proposed, but in vivo its
contribution to TRAP-related changes in brain morphology remains
inconclusive. We investigated these questions using cranial magnetic
resonance imaging (MRI) data. Based on cranial MRIs from the
population-based ‘Cooperative Health Research in the Region of Augsburg’
cohort, we analyzed global and region-specific white matter lesions,
cerebral microbleeds, brain volumes, and olfactory bulb signal intensity
in 400 participants. Land-use regression models estimated residential
long-term exposure to air pollutants, including particle number
concentration, particulate matter with different diameters, coarse
particulate matter with a diameter between 10 μm and 2.5 μm, absorbance
of particulate matter with an aerodynamic diameter ≤2.5 μm, and nitrogen
oxides. We used covariate-adjusted regression models to explore the
association between TRAP and white matter lesions, brain volumes, or
cerebral microbleeds, and investigated whether the olfactory bulb
mediates this association. Participants’ mean age was 56 ± 9 years, and
42% were female. We found that TRAP was associated with increased odds
of prevalent white matter lesions. For global white matter lesions, an
interquartile range increase in absorbance of particulate matter was
associated with an odds ratio of 1.48 [95% CI: 1.02; 2.14]. Comparable
results were found for non-frontal white matter lesions, where nitrogen
dioxide, absorbance of particulate matter, and coarse particulate matter
were linked to increased odds of white matter lesions. In the mediation
analysis we did not find evidence that the association was mediated by
the signal intensity of the olfactory bulb. Stratified analyses revealed
that women were more susceptible for the detrimental effects of TRAP.
Our findings suggest that TRAP exposure was associated with an increased
odds for white matter lesions, while the olfactory bulb did not appear
to mediate this relationship.