Most people are familiar with type 1 and type 2 diabetes mellitus, but type 3 diabetes may be a novel term for many. The term “type 3 diabetes” has been used by researchers to describe Alzheimer’s disease, now sometimes referred to as “diabetes of the brain”.^1,2

How Is Diabetes Related to Alzheimer’s?  

Alzheimer’s disease is a type of dementia caused by the degeneration of cells in the brain that leads to severe cognitive decline and impairment of daily activities.^3,4 Type 2 diabetes mellitus on the other hand is the most common type of diabetes, characterized by the non-autoimmune loss of pancreatic b-cell insulin secretion and insulin resistance, which results in persistent hyperglycemia.⁵ These two diseases on the surface may seem unrelated, but recent research is indicating that Alzheimer’s disease may represent a brain-specific diabetes.² The term “type 3 diabetes” highlights the shared cellular and molecular features of both illnesses as well as the significant role insulin resistance may play in cognitive decline. Studies have also been showing that type 2 diabetes is associated with an increased risk of dementia and Alzheimer’s disease.⁶

How Does Insulin Resistance Affect Alzheimer’s?

Numerous factors play a role in the development of Alzheimer’s disease, and the relationship between diabetes and Alzheimer’s is complex and still under study. However, research is showing that insulin and insulin signaling affect a wide array of neural functions including glucose homeostasis in the brain, regulation of neurotransmitters, neuronal and synaptic integrity, and cognition.² In addition, researchers are discovering that insulin plays an important role in clearing beta-amyloid plaques and tau protein, key contributors to cognitive decline in Alzheimer’s disease.³ Given the evidence, the development of insulin resistance, hyperglycemia, and ineffective glucose uptake by the brain seems to affect various neural functioning, allow build-up of harmful plaques and tangles in the brain, and contribute to cognitive decline.

What Should I Do If I Have Diabetes?  

Alzheimer’s disease is caused by an interplay of various genetic and environmental factors, and more research is needed to further elucidate the underlying pathological mechanisms and to discover new therapeutic approaches to Alzheimer’s disease.³ Some researchers call for diabetes to be considered as a risk factor for Alzheimer’s disease and highlight the importance of routine testing of fasting glucose, fasting insulin, and measures of insulin resistance.⁶ Given the research indicating the potential role of insulin resistance in cognitive decline, utilizing lifestyle and pharmacological interventions to achieve and maintain glycemic target can be important in individuals with diabetes.³

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