Almost all of us worry about becoming dependent on others and losing our independence as we age.  Having treated patients with Alzheimer’s dementia for years, I can tell you the loss of my faculties scares the daylights out of me.  We know that diabetes, heart disease, and stroke have all associated with mental decline and potentially dementia.  The question is if obesity and an elevated body mass index (BMI) are also associated with an elevated risk of developing dementia.  

A meta-analysis published in November of 2017 looked at this very subject by pooling the data from 1.3 million adults from 39 prospective cohort studies​[1]​.  The researchers examined this hypothesis in over 1.3 million dementia-free participants from 39 cohort studies.  BMI was assessed at baseline.  Dementia in 6894 patients was ascertained at follow-up using electronic health records.  The researchers calculated a hazard ratio at 10 years, 10-20 years, and >20 years before dementia diagnosis which basically determines the hazard of developing dementia.  The researchers felt there was a link between BMI and dementia.  The connection was perceived to be likely one of two different processes: a harmful effect of higher BMI, which is observable in extended follow-up, and a reverse-causation effect that makes a higher BMI appear to be protective when the follow-up is short.  I would suggest that the cause could also be the insulin resistance caused by excess central obesity but to be honest, this study cannot determine causation.  

The bottom line: Use this study as motivation to lose weight.  It is not earth-shattering.  In this study, a higher BMI was associated with an increased risk of dementia.  Most research is needed because there is a significant limitation in this study.