Can chronic hyperglycemia and insulin resistance damage blood vessels and affect cognition?

Chronic hyperglycemia and insulin resistance are strongly linked to systemic endothelial injury and are credibly connected to brain small-vessel disease and impaired cerebral glucose metabolism. For a 77-year-old man, these pathways are clinically relevant because vascular and neurodegenerative processes may coexist and compound cognitive risk.

Vascular and cerebral microvascular evidence

• Hyperglycemia and insulin resistance promote endothelial dysfunction with strong mechanistic and clinical support. In complicated type 2 diabetes, flow-mediated dilation (FMD) was approximately 4.26 percentage points lower; each 1 mmol/L higher fasting glucose was associated with a 0.52% reduction in FMD. A pooled analysis of 12 studies also found a significant association between insulin resistance and endothelial dysfunction.
• Cerebral small-vessel injury is plausible rather than conclusively established. Higher baseline HbA1c predicted greater 2-year white-matter-hyperintensity progression, particularly at diabetic HbA1c levels. In adults without diabetes, higher HOMA-IR and lower insulin sensitivity were associated with lacunes and severe white-matter hyperintensities.

Mechanistic basis

• Hyperglycemia increases endothelial reactive oxygen species through NADPH oxidase, polyol, advanced-glycation-end-product, and PKC pathways. Reactive oxygen species quench nitric oxide and impair eNOS function.
• Insulin resistance also disrupts endothelial PI3K–Akt–eNOS signaling, reducing nitric-oxide-mediated vasodilation. These converging pathways provide a biologically coherent route from metabolic dysfunction to vascular injury.

Brain energy use and cognition

• In prediabetes/early type 2 diabetes, greater insulin resistance was associated with lower FDG-PET glucose metabolism in frontal, temporoparietal, posterior-cingulate, and precuneus regions. Among older adults, Alzheimer-pattern hypometabolism occurred in 48.1% with diabetes versus 28.9% without diabetes.
• A small randomized intranasal-insulin trial found better delayed recall, preserved function, and less FDG-PET hypometabolism progression, although pooled cognitive-treatment findings are inconsistent.

Bottom line

• Metabolic insulin resistance and hyperglycemia clearly impair endothelial function and are supported contributors to disrupted cerebral glucose use and cognition; their role in cerebral microvascular MRI injury is well-grounded but less definitively causal.