Abstract
BACKGROUND AND AIM: Several studies suggest associations between road traffic noise and incidence of dementia. However, findings are inconsistent when air pollution, a recognized risk factor for dementia, is considered. We investigated associations between air pollution, road traffic noise and incident dementia. METHOD: We followed 26,461 women from the Danish Nurses Cohort from baseline (1993 or 1999) to their first hospital contact or first prescription of dementia medication whichever came first until 2021 using Danish registers. Annual air pollution (PM2.5 and NO2) and road traffic noise estimates (Lden) were modelled at nurses’ residential address using DEHM/UBM/AirGIS and Nord2000 models, respectively. We applied time varying Cox models to estimate associations between 10- year running mean air pollution, noise and incident dementia. Models were adjusted for baselines year, individual lifestyle, socio-economic factors and municipality characteristics. RESULTS: A total of 1557 incident cases of dementia were during the follow up. Median exposures were 12.18 µg/m³ with interquartile range (IQR) of 5.79 µg/m³ for PM2.5, 16.51 µg/m³ (IQR 8.25µg/m³) for NO2 and 53.2 dB (IQR 9.3 dB) for Lden. We detected moderate associations between dementia incidence and PM2.5, with hazard ratio of 1.35 per IQR and 95% confidence interval (1.20-1.51), or NO2 (1.19; 1.09-1.29) and a weak positive association with Lden (1.04; 0.97-1.13). Associations with NO2 and Lden diminished when adjusting for PM2.5 with hazard ratios of 0.98 (0.86-1.12) and 0.95 (0.88-1.00) respectively. CONCLUSIONS: Our results shows a weak association between road traffic noise or traffic related pollutants and incident dementia, which may be partially explained by the effects of PM2.5.