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Background: Dementia is a global public health challenge, with Alzheimer's disease (AD) and vascular dementia (VaD) being the most prevalent subtypes. Air pollution is a potential risk factor for dementia, but few studies separate AD and VaD.

Objective: This study aims to investigate whether exposure to air pollution is associated with the incidence of AD and VaD.

Methods: This study involved 30,247 participants from the Malm & ouml; Diet and Cancer Study (1991-2014), with 1216 AD cases (including mixed type) and 531 VaD cases, clinically validated. Long-term exposure to PM2.5 and NOx was modeled using the past 5-years or 10-year mean concentration with 50m x 50 m spatial resolution at residential addresses. The association between AD and VaD and air pollution was assessed using adjusted Cox-proportional hazards.

Results: For AD the hazard ratios (HRs (95% CIs) were 1.06 (0.89-1.27) for PM2.5 and 1.08 (0.96-1.22) for NOx per interquartile range (IQR) increase in past 10-year mean pollution-levels. Nonsignificant associations were observed in two-pollutant models. For past 5-year exposure, we observed a statistically significant association between NOx and AD 1.14 (1.00-1.30). For VaD, we found no evidence for associations in any models.

Conclusions: We found that while both PM2.5 and NOx seemed linked to increased AD risk in single-pollutant models, only the associations with NOx remained in two-pollutant models, particularly for exposures in the past five years. No associations were observed for VaD. The results underscore the importance of distinguishing dementia subtypes, identifying critical exposure windows, and applying multi-pollutant models in future studies.