LONG-TERM EXPOSURE TO NITROGEN DIOXIDE AND BRAIN CORTICAL THINNING

Despite growing evidence on the clinical outcomes related to cognitive decline, there are only a few studies on subclinical brain outcomes associated with ambient air pollution using magnetic resonance imaging (MRI). Moreover, the findings are inconsistent across brain regions. This study aimed to explore brain regions associated with nitrogen dioxide (NO2) levels using cortical thickness (a more sensitive indicator of brain structural changes than cortical volumes) in a community-based cohort. This study included 427 men and 530 women dwelling in four cities (Seoul, Incheon, Wonju, and Pyeongchang) in South Korea. Surface-based cortical thickness was estimated from region-of-interest analysis of brain 3T MRI images. Generalized linear models included cumulative five-year NO2 levels, age, education level, body mass index, intracranial volume, and other cardiovascular confounders, separately by sex. In men, one ppb increase in NO2 was associated with a decline in global (β=−0.002, SE=0.000, p<0.001), frontal (β=−0.003, SE=0.000, p<0.001), parietal (β=−0.003, SE=0.001, p<0.001), temporal (β=−0.005, SE=0.000, p<0.001), and insula thickness (β=−0.002, SE=0.001, p=0.001). In women, one ppb increase in NO2 was associated with a decline in frontal (β=−0.001, SE=0.001, p=0.008) and temporal thickness (β=−0.003, SE=0.001, p<0.001). There were significant associations between higher NO2 and decreased volumes of several subcortical structures (the thalamus, caudate, amygdala, and nucleus accumbens in men; the thalamus, pallidum, amygdala, and nucleus accumbens in women). Long-term NO2 levels were significantly associated with cortical thinning in the frontal and temporal lobes and decreased volumes of the thalamus, amygdala, and nucleus accumbens in both men and women without known neurological disorders.