Body mass index (BMI) at an early age and the risk of dementia.

BMI change and BMI at an early age have not been investigated as risks for dementia. This case-control study included 286 dementia patients and 268 controls from two medical centers between 2007 and 2009. BMI information was collected from medical records and questionnaires. Men and women with low BMIs at the time of the study, in their 20s, and in their 40s had significantly increased risks of Alzheimer's disease (AD) (odds ratio = OR = 2.62-3.97) and increased vascular dementia (VaD) risk (20s and 40s: OR = 6.23-11.11) compared with those with normal BMIs. High BMI in the 20s and 40s was associated with increased VaD risk (OR = 15.29 and 10.32) among women. For BMI changes from the 20s or 40s, the second and third tertiles were significantly associated with decreased AD risk among women (OR = 0.15-0.35) compared to the first tertile. The third tertile of BMI change from the 20s or 40s was associated with decreased VaD risk among women (OR = 0.06 and 0.14). Low BMIs in the 20s and 40s were stronger predictors of AD and VaD. There was a U-shaped association between BMI at different ages and dementia among participants with VaD.