Abstract
Objectives: Identifying whether obesity is a risk factor for dementia is complicated by the possibility of weight change as dementia evolves. This article investigates an extended time path of body mass index (BMI) before and after incident dementia in a nationally representative sample. Methods: Using the Health and Retirement Study (2000-2016), we examine (1) the longitudinal relationship between BMI and incident dementia and (2) heterogeneity in the BMI trajectory by initial BMI level. Results: Weight loss begins at least one decade before incident dementia, then accelerates in the years immediately preceding dementia onset and continues after incident dementia. Those with higher levels of BMI at baseline experienced a much greater decline relative to those with a normal weight. Discussion: Our results help explain the contradicting findings in the literature regarding the relationship between obesity and dementia and highlight the need for using extended longitudinal data to understand dementia risk.