found no evidence of a moder- ating effect of APOE on the relationship between air pollution and dementia. A previous study using data from the Betula Project [27] used NOx as exposure variable and found no modifying effect of APOE.The aim of this study was to investigate the associa- tions between PM2.5 exposure and dementia, in a low exposure area. Furthermore, we wanted to increase the understanding of the role of olfaction and the APOE 4 allele in the associations between air pol- lution and dementia.