Why Is Alzheimer's Called Type 3 Diabetes?

A Diabetic Testing Her Blood Sugar/ ballyscanlon/Digital Vision/ Getty Images.

Alzheimer's disease is a type of progressive dementia that affects more than 5 million Americans, and those rates are projected to increase dramatically over the next several years.

One link to Alzheimer's disease that researchers are exploring is diabetes, specifically type 2 diabetes. Type 2 diabetes develops when insulin becomes less efficient at processing sugar through the bloodstream. Studies show that approximately half of people with type 2 diabetes will go on to develop Alzheimer's disease.

With such a strong connection, the focus of some research studies is to explain the connection between the two disease.

Why Is Alzheimer's Called "Type 3 Diabetes?"

Some researchers have begun to call Alzheimer's disease "type 3 diabetes." Why? In type 1 or 2 diabetes, not enough insulin (or none at all) is produced to process glucose (sugar) correctly or the body no longer responds to insulin, and it affects the functioning on the whole body. In Alzheimer's disease, it appears that a similar problem is occurring, but instead of causing problems in the entire body's functioning, the effects occur in the brain.

Researchers found interesting evidence of this when they studied people's brains after their death. They noted that the brains of those with Alzheimer's disease who did not have type 1 or type 2 diabetes showed many of the same abnormalities of those with diabetes, including reduced levels of insulin in the brain.

This led researchers to conclude that perhaps Alzheimer's is a brain-specific type of diabetes which they termed "type 3 diabetes."

In diabetes, if a diabetic person's blood sugars become too high or too low, the body sends very obvious signs of the problem- behavior changes, confusion, seizures, etc.

In Alzheimer's disease, however, rather than those acute signals of a problem, the brain's function and structure decline gradually over time.

When a group of researchers reviewed the collections of studies available on Alzheimer's disease and brain function, they noted that a common finding in Alzheimer's disease was the deterioration of the brain's ability to use and metabolize glucose. They compared that decline with cognitive ability, and noted that the decline in glucose processing coincided with, or even preceded, the cognitive declines of memory impairment, word-finding difficulty, behavior changes and more.

Furthermore, scientists determined that as insulin functioning in the brain worsens, not only does the brain's cognitive ability decline, the size and structure of the brain also deteriorate- all things that occur as Alzheimer's disease progresses.

Does Type 2 Diabetes Cause Alzheimer's Disease?

Research is ongoing about this question, but one study suggests that while diabetes likely exacerbates and contributes to the development of Alzheimer's disease, it is likely not the sole cause of it.

In this study, scientists fed mice a high fat diet which induced the development of type 2 diabetes. They then studied the mice and found that a higher amount of tau protein was present in their brains, and the mice also developed a resistance to brain insulin. Additionally, the brain structure of these mice also deteriorated somewhat on the high fat diet; however, the cognitive functioning of these mice did not decline significantly to the level they would if Alzheimer's disease was present.

Looking at What Causes Alzheimer's Disease
So, what does cause Alzheimer's if type two diabetes is not the culprit? Researchers have for decades been attempting to determine the specific cause of Alzheimer's disease. While they can diagnose it conclusively with an autopsy of the brain because they know what it looks like and how it affects the structures of the brain, they haven't been able to figure out for certain what really triggers the changes in the brain that are noted in Alzheimer's.

Scientists have, however, determined several ways to reduce your risk of developing Alzheimer's disease, including a healthy diet, physical activity and mental stimulation, among many others.

Can Diabetes Medications Treat Alzheimer's Disease?

If Alzheimer's disease is another type of diabetes, would medications for diabetes help people with Alzheimer's? Several research studies have looked at this possibility and seem to indicate that this may be possible. In both animal and human studies, research has demonstrated that these insulin medications have protected against the structural abnormalities that develop in Alzheimer's disease, have improved the brain's ability to metabolize glucose, and have even demonstrated an improvement in the brain's cognitive functioning.

One of those studies is outlined here:

Insulin Sensitizer Demonstrates Positive Results for Alzheimer's Disease


Alternative Medicine Review.Volume 14, Number 4, 2009. The Relationship between Alzheimer’s Disease and Diabetes: Type 3 Diabetes? http://www.thorne.com/altmedrev/.fulltext/14/4/373.pdf

Alzheimer's Association. Alzheimer’s Disease and Type 2 Diabetes: What Is the Link? April 2011. http://www.alz.org/national/documents/topicsheet_diabetes.pdf

Archives of Neurology. 2012;69(1):29-38. Intranasal Insulin Therapy for Alzheimer Disease and Amnestic Mild Cognitive Impairment. http://archneur.jamanetwork.com/article.aspx?articleid=1107947

International Conference on Alzheimer's Drug Discovery. Metabolic Solutions Development Company presents Phase 2a clinical trial results. September 9, 2013. http://www.msdrx.com/wp-content/uploads/MSDC-AD-Study-Results-Presentation-at-ADDF-REVISED-FINAL-090613.pdf

Journal of Diabetes Science and Technology. 2008 November; 2(6): 1101–1113. Published online 2008 November. Alzheimer's Disease Is Type 3 Diabetes–Evidence Reviewed. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2769828/

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