APOE and dementia: In this long-term population-based longitudinal cohort of dementia-free older adults, we found that (a) BMI/weight change over 6 years had a U-shaped association with incident dementia; (b) large BMI/weight loss and gain alike were related to increased dementia risk after adjustment for potential confounders; and (3) the risk of dementia was especially high for APOE ɛ4 carriers who experience large BMI/weight loss or gain.