Elevated body mass index, dementia risk, and post-mortem neuropathology

Over two-thirds of Americans aged 20 and over are considered overweight or obese. Compared to those who are within the healthy weight range as determined by body mass index (BMI), overweight and obese individuals are higher risk for poorer cognitive performance and structural brain pathology on neuroimaging studies. In addition, previous studies have shown a positive association between elevated BMI and the development of dementia later in life. In this study, we assessed for associations between overweight or obese BMI and dementia as well as for associations between overweight or obese BMI and neuropathology findings. METHODS: Study participants were selected from a larger longitudinal dataset collected by the National Alzheimer’s Coordinating Center. The inclusion criteria for this study included having records for BMI 10 to 15 years prior to death as well as neuropathology data. Individuals who were underweight were excluded. A cross-sectional study design was used to assess for associations between elevated BMI categories and dementia. To assess for associations between elevated BMI categories and severity of neuropathology findings, a cohort study design was used. Logistic regression was used to determine odds ratios and their corresponding confidence intervals for all analyses. RESULTS: There were no significant associations between individuals having overweight BMI or obese BMI and having a diagnosis of dementia. However, individuals who were overweight or obese had higher odds of having dementia when they carried an APOE4 allele or completed less than a college-level education. There were no significant associations between elevated BMI categories and neuropathology findings, except for lower odds of hippocampus atrophy among obese individuals. DISCUSSION: The lack of significant positive associations between elevated BMI categories and dementia may be due to the lower number of subjects with dementia who met the inclusion criteria for the study. The lack of significant positive associations between elevated BMI categories and more severe neuropathology findings may be due to the higher proportion of participants in this study having characteristics associated with higher socioeconomic status. Over 90% of subjects identified as white and over 60% of subjects completed at least a college-level education. This study did not account for the chronicity of exposure to elevated BMI nor other lifestyle factors such as physical activity, dietary intake, and substance use that affect brain health.