Does insulin therapy for type 1 diabetes mellitus protect against Alzheimer's disease?

Alzheimer's disease is the most common cause of dementia in the United States. A better understanding of the disease's underlying pathways may provide novel treatment and/or prevention strategies for this progressive chronic neurodegenerative disorder. In recent years, there has been a growing interest in the possible links between insulin and Alzheimer's disease. Insulin-induced hypoglycemia causes adaptive changes in the brain, including an improved ability to use alternative fuels. Insulin has been shown to facilitate reduction of intracellular amyloid plaque and downregulation of amyloid-β-derived diffusible ligand-binding sites. Insulin also promotes tau hypophosphorylation, which stabilizes microtubules and promotes tubulin polymerization. Excess exogenous insulin may also play a role in overcoming the decreased utilization and transport of glucose in patients with Alzheimer's disease. Intranasal insulin therapy may have beneficial effects on cognition and function in patients with Alzheimer's disease, as well as having only minor adverse effects, and this route of administration been the focus in clinical trials. These data support the mechanistic pathways that might link excess exogenous insulin administered to patients with type 1 diabetes mellitus to possible protection from Alzheimer's disease and provide a rationale for using insulin to prevent the disease in high-risk patients.