Diabetes, sugar-coated but harmful to the brain.

Type 2 diabetes mellitus appears to directly impair cognition and brain function, independent of its associated cardiovascular disease. This is supported by the presence of similar findings among adults with insulin resistance (pre-diabetes) and obese children with type 2 diabetes, years before overt cardiovascular disease. Hippocampal based memory performance is impaired early in the disease, although deficits in executive function, attention, and psychomotor speed are also seen in more chronic disease and/or poorer disease control, particularly in the presence of co-morbidities such as hypertension. Although there has been some speculation as to possible links between diabetes and Alzheimer's Disease based on associations found in population studies, no convincing empirical evidence has been put forth and brain autopsy studies, the gold standard of Alzheimer's diagnosis, have not supported such a link. Future studies should focus on understanding the mechanisms for the cognitive impairments associated with type 2 diabetes. We propose that insulin resistance-associated impairments in vascular reactivity and endothelial function are possible candidates as they may impact substrate delivery across the blood-brain-barrier. These are important issues given the obesity epidemic and the associated rising prevalence of insulin resistance and type 2 diabetes.