Supplementary Material for: Environmental factors and risk of early-onset dementia: a population-based case-control study

Introduction: Dementia with symptom onset before the age of 65 is referred to as early-onset dementia (EOD). Many gaps exist regarding EOD etiology, including the role of environmental factors. Methods: We conducted a population-based case-control study in Modena province, Northern Italy, enrolling and geocoding 326 EOD cases and 1941 sex- and age-matched controls, to investigate the association of traffic-related benzene, green spaces around the place of residence, and exposure to artificial outdoor light at night. We used non-linear modeling to assess the relation between environmental variables and disease risk, overall and separately for Alzheimer’s dementia (AD) and non-AD. Results: Green spaces generally showed an inverse association with EOD risk that was almost linear for AD and inverted U-shaped for non-AD. We observed a weak positive association between traffic-related benzene exposure and EOD risk that seemed limited to AD, with little change in risk for non-AD. Exposure to light at night showed an inverse linear association with small differences across the two disease subgroups. Analyses stratified by sex and age showed generally stronger (but statistically imprecise) associations in females and older individuals. Conclusion: Overall, these results are consistent with some environmental influences on EOD risk, particularly with a beneficial effect of green spaces and light at night, as well as a possible adverse role of air pollution, particularly for AD.