Increased risk of dementia in patients exposed to nitrogen dioxide and carbon monoxide: a population-based retrospective cohort study

Abstract

Background: The air pollution caused by vehicular emissions is associated with cognitive decline. However, the associations between the levels of nitrogen dioxide (NO2) and carbon monoxide (CO) exposure and dementia remain poorly defined and have been addressed in only a few previous studies.

Materials and methods: In this study, we obtained data on 29547 people from the National Health Insurance Research Database (NHIRD) of Taiwan, including data on 1720 patients diagnosed with dementia between 2000 and 2010, and we evaluated the risk of dementia among four levels of air pollutant. Detailed data on daily air pollution were available from January 1, 1998 to December 31, 2010. Yearly average concentrations of pollutants were calculated from the baseline to the date of dementia occurrence, withdrawal of patients, or the end of the study, and these data were categorized into quartiles, with Q1 being the lowest level and Q4 being the highest.

Results: In the case of NO2, the adjusted hazard ratios (HRs) of dementia for all participants in Q2, Q3, and Q4 compared to Q1 were 1.10 (95% confidence interval (CI), 0.96-1.26), 1.01 (95% CI, 0.87-1.17), and 1.54 (95% CI, 1.34-1.77), and in the case of CO, the adjusted HRs were 1.07 (95% CI, 0.92-1.25), 1.37 (95% CI, 1.19-1.58), and 1.61 (95% CI, 1.39-1.85).

Conclusion: The results of this large retrospective, population-based study indicate that exposure to NO2 and CO is associated with an increased risk of dementia in the Taiwanese population.

Figure 1. Probability free of dementia among quartiles of yearly average concentration in NO₂.

Figure 2. Probability free of dementia among quartiles of yearly average concentration in CO.