Personally, living with two T1D ( type 1 insulin dependent diabetic, the autoimmune disease not to be confused with the i am old, fat and over eat disorder) when your blood sugar is too high or low , you act weird , you are in a fog . Long term effects of the swings and sustained levels cause brain damage, not necessarily traumatic brain injuries but damage nonetheless.
So i can see the correlation for T1D and undiagnosed T2D cases Alzheimers. Now having a parent with both T2D and Alzheimers when they were taking rebelsis there was a change in their overall mood and activity , but i saw the change was "hey your sugar is under control, and no i am not your buddy from the army" . To be clear the difference is the fog of being unclear about what's going on like you're drunk , vs the grand delusions of seeing a different person that's not there .
This should have been obvious for the researchers.
