We aim to investigate the association between exposure to long-term air pollution and dementia, and to clarify the role played by CVDs.

Emerging – yet contrasting- evidence associates air pollution with incident dementia, and no studies have examined the role of cardiovascular diseases (CVDs) in this association.

2,927 dementia-free adults of the Swedish National study on Aging and Care in Kungsholmen (SNAC-K) were examined for up to 13 years. Two major air pollutants (particulate matter ≤2.5μm, PM_2.5 and nitrogen oxides, NO_X) were assessed yearly, using dispersion models for outdoor levels at residential addresses. The hazard of dementia was estimated using Cox models. The potential modifier and mediating effects of CVDs (i.e. atrial fibrillation, ischemic heart disease, heart failure and stroke) were tested using stratified analyses and generalized structural equation modeling.

Within the five years prior to incident dementia and after controlling for potential confounders, we observed an up to 50% increased hazard of dementia per interquartile range difference in average pollutant levels at residential address (HR:1.15;95%CI:1.03-1.29 for NOx; HR:1.52;95%CI:1.33-1.75 for PM_2.5). The results were attenuated during longer follow-up. Heart failure and ischemic heart disease enhanced the dementia risk, while the development of stroke seemed to be the intermediate condition that explained up to 50% of dementia cases.

Long-term exposure to air pollution is associated with a higher risk of dementia. Cardiovascular diseases amplified the negative effect of air pollution. Heart failure and ischemic heart disease enhanced the dementia risk, while stroke seemed to be an important intermediate condition between air pollution exposure and dementia.