Association Between Body Mass Index and Incident Dementia Among Community-Dwelling Older Adults: The Shanghai Aging Study1

Abstract

Background: 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. Objective: This study aimed to examine the association between BMI and incident all-cause dementia among Chinese older adults using a prospective study. Methods: 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. Results: 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. Conclusion: Our result indicates that low BMI may contribute to high risk of incident dementia, even in individuals without central obesity.