Association Between Body Mass Index and Incident Dementia Among Community-Dwelling Older Adults: The Shanghai Aging Study.

Abstract

The relationship between body mass index (BMI) and dementia is inconclusive. Undesirable loss of fat-free mass is a risk factor for cognitive decline while obesity is also a risk factor for cardio-metabolic disorders among the older adults. This study aimed to examine the association between BMI and incident all-cause dementia among Chinese older adults using a prospective study. Participants were 1,627 community residents aged 60 or older without dementia from the Shanghai Aging Study. Cox regression models, incorporated with restricted cubic splines, were used to explore a nonlinear association between baseline BMI and risk of all-cause dementia as measured by hazard ratio (HR) using both frequentist and Bayesian approach. We diagnosed 136 incident dementia cases during the mean follow-up of 5.3 years. Compared with moderate BMI (18.5-24.0 kg/m2), low BMI (< 18.5 kg/m2) were related to an increased risk of dementia with the HR as 3.38 (95% CI 1.50-7.63), while high BMI (≥24.0 kg/m2) showed a decreased risk of dementia without statistical significance (HR = 0.91, 95% CI 0.60 to 1.39). Sensitivity analysis in participants without central obesity indicated that the association was still significant with even higher HR. Bayesian approach presented the similar results. Our result indicates that low BMI may contribute to high risk of incident dementia, even in individuals without central obesity.