A study published in the journal Alzheimer′s & Dementia revealed that obesity in middle age may raise the risk of dementia. The link between BMI and the risk of dementia, however, is still not obvious. In the study, researchers found that different patterns of BMI change over one′s life course may be an indicator of a person′s risk for dementia.

The author of the study explained that the previous studies that looked at the trajectories did not consider how patterns of weight gain, stability, or loss can be a signal that dementia is potentially imminent. In the study, a group of participants was followed for 39 years, and their weight was measured approximately every 2–4 years.

The findings of the study showed that a declining BMI was associated with a higher risk of developing dementia. However, they also found that in some patients there was an initial increase in BMI followed by a decline in BMI, both occurring within midlife, which appeared to be central to the declining BMI-dementia association. 

(Source: https://www.hindustantimes.com/lifestyle/health/study-reveals-association-between-bmi-risk-of-dementia-101671117898729.html )