In this longitudinal study of dementia-free NACC participants, exposure to vitamin D was associated with higher dementia-free survival and lower dementia incidence rates over 10 years. These findings were consistent across each vitamin D formulation: calcium–vitamin D, cholecalciferol, and ergocalciferol. Interaction analyses revealed that while exposure to vitamin D was associated with lower dementia incidence across all strata of sex, cognitive diagnosis, and APOE ε4 status, the rates were lower in females versus males, NC versus MCI, and APOE ε4 non-carriers versus carriers…