APOE and dementia: Using a life-course approach, this study aims to test the hypotheses that (1) cognitive reserve-related factors operating at various life periods each are potentially associated with decreased risk of the occurrence of dementia, (2) cumulative exposure to reserve-related factors is associated with a progressively reduced risk of dementia, and (3) the risk of dementia later in life is influenced by the interaction between lifelong exposure to cognitive reserve-related factors and genetic factors (e.g., apolipoprotein E [APOE] ε4).