Evidence regarding the association of specific air pollutants with vascular dementia (VaD) risk is limited. In this nested case-control study, we enrolled 831 adults aged >65 years with VaD (International Classification of Diseases, Ninth Revision, Clinical Modification code 290.4x) newly diagnosed during 2005-2013; 3324 controls were age-, sex-, and VaD diagnosis year-matched with the study patients. Both patients with VaD and controls were selected from among a cohort of one million beneficiaries of Taiwan's National Health Insurance program, all of whom were registered in 2005. Exposure to the mean daily air pollutant concentration, derived from 76 fixed air quality monitoring stations, in 3, 5, and 7 years before VaD diagnosis was assessed using the spatial analysis method (i.e., ordinary kriging) on ArcGIS. A logistic regression model was used to calculate covariate-adjusted odds ratios (ORs) of VaD in relation to specific air pollutants. After potential confounders and other air pollutants were controlled for, high concentrations of coarse particulate matter (10 µm or less in diameter) and carbon monoxide (CO) were sporadically associated with higher OR of VaD. The most prominent association was observed for nitrogen dioxide (NO₂) exposure within 5 and 7 years before diagnosis. Compared with the <25th percentile of NO₂ exposure, the 25th-50th, 50th-75th, and >75th percentiles of NO₂ exposure significantly increased ORs (95% confidence intervals): 1.62 (1.28-2.23), 1.61 (1.11-2.33), and 2.22 (1.35-3.65) within 5 years before diagnosis, respectively, and 1.59 (1.20-2.11), 1.65 (1.15-2.37), and 2.05 (1.28-3.28) within 7 years before diagnosis, respectively. We found that higher NO₂ exposure in the past was significantly associated with an elevated risk of VaD. Although less consistent, higher exposure to CO was also associated with a higher risk of VaD. Most NO₂ in cities originates from motor vehicle exhaust; other sources of NO₂ are petrol and metal refining, electricity generation from coal-fired power stations, other manufacturing industries, and food processing. Future studies should investigate associations of VaD with specific sources of NO₂.

Chien-Hsin Li

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