Long-term exposure to air pollution and road traffic noise and incidence of dementia in the Danish Nurse Cohort

INTRODUCTION We examined the association of long-term exposure to air pollution and road traffic noise with dementia incidence in the Danish Nurse Cohort. METHODS Female nurses were followed for dementia incidence (hospital contact or medication prescription) from 1993/1999 to 2020. Air pollution and road traffic noise levels were estimated at nurses' residences, and their associations with dementia were examined using Cox regression models. RESULTS Of 25,233 nurses 1409 developed dementia. Particulate matter with a diameter of <= 2.5 mu m (PM2.5) was associated with dementia incidence, after adjusting for lifestyle, socioeconomic status, and road traffic noise (hazard ratio [95% confidence interval] 1.35 [1.15-1.59] per interquartile range of 2.6 mu g/m(3)). There was no association of PM2.5 with dementia in physically active nurses. Association with road traffic noise diminished after adjusting for PM2.5 (1.02 [0.93-1.11] per 7.6 dB). DISCUSSION Long-term exposure to air pollution increases risk of dementia, and physical activity may moderate this risk.