A small study comparing 18 obese adolescents with type 2 diabetes and equally obese adolescents without diabetes or pre-diabetes has found that those with diabetes had significantly impaired cognitive performance, as well as clear abnormalities in the integrity of their white matter (specifically, reduced white matter volume, especially in the frontal lobe, as well as impaired integrity in both white and grey matter). Similar abnormalities have previously been found in adults with type 2 diabetes, but the subjects were elderly and, after many years of diabetes, generally had significant vascular disease. One study involving middle-aged diabetics found a reduction in the volume of the hippocampus, which was directly associated with poor glycaemic control.
It remains to be seen whether such changes can be reversed by exercise and diet interventions. While those with diabetes performed worse in all cognitive tasks tested, the differences were only significant for intellectual functioning, verbal memory and psychomotor efficiency.
(2010). Preliminary evidence for brain complications in obese adolescents with type 2 diabetes mellitus.
(2007). Hippocampal damage and memory impairments as possible early brain complications of type 2 diabetes.
Diabetologia. 50(4), 711 - 719.