Why Alzheimer's Disease Is Called Type 3 Diabetes

Someone pricking their finger to test blood sugar levels
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You've heard of type 1 diabetes, and type 2 diabetes, but have you heard of type 3 diabetes? Alzheimer's disease, a type of progressive dementia that affects more than 5 million Americans, has been found to be strongly linked to diabetes, leading researchers to nickname it "type 3 diabetes."

In fact, according to the American Diabetes Association, having diabetes or prediabetes is the second biggest risk factor in the development of Alzheimer's disease, aside from advanced age. Although a small amount of research found an increased risk of dementia with type 1 diabetes, the vast majority of studies have concluded that this link between diabetes and Alzheimer's is specific to type 2 diabetes.

Alzheimer's and Diabetes

The stats are staggering: Studies show that approximately half of the population with type 2 diabetes will go on to develop Alzheimer's disease and that having diabetes can increase a person's risk of developing Alzheimer's by 65 percent. With such a strong connection, recent research has focused on explaining the connection between the two diseases.

Type 2 diabetes develops when insulin becomes less responsive to glucose (sugar) and less efficient at removing glucose out of the bloodstream, causing it to build up rather than being taken into the cells to be used for energy.

In type 1 diabetes, the cells which produce insulin, called beta cells, are attacked by the body's own immune system, again causing glucose to build up to high levels in the bloodstream.

In Alzheimer's disease, it appears that a similar problem of insulin resistance occurs, but instead of causing problems in the body as a whole, the effects are localized in the brain.

Type 3 Diabetes

Researchers found interesting evidence of this when they studied people's brains after 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 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 of which normally occur as Alzheimer's disease progresses.

Does Type 2 Diabetes Cause Alzheimer's Disease?

Research is ongoing, but recent studies suggest that while diabetes likely exacerbates and contributes to the development of Alzheimer's disease, it is probably not the sole cause of it.

Scientists have discovered that diabetes complications can affect brain health in various ways:

  • By raising the risk of heart disease and stroke, which can lead to damaged blood vessels, and damaged or constricted blood vessels can contribute to reduced blood flow to the brain, resulting in dementia.
  • By leading to an excess of insulin, which may alter the amount or status of other neurochemicals reaching the brain, and this imbalance may lead to Alzheimer's.
  • By resulting in elevated blood sugar, which leads to inflammation, and this inflammation may damage brain cells and trigger Alzheimer's.

Looking for the Cause of Alzheimer's Disease

For decades, researchers have attempted to determine the specific cause of Alzheimer's disease. While they can now diagnose it conclusively with an autopsy of the brain and can see how the amyloid plaques characteristic of Alzheimer's can affect the structure of the brain, they haven't been able to figure out for certain what 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.

Diabetes Medications and Alzheimer's Treatment

Amazingly, diabetes medications have been shown to help with Alzheimer's. Several research studies have begun to look at this possibility and indicate that this is possible. In both animal and human studies, research has demonstrated that medications improving insulin sensitivity 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 in some cases.

A Word From Verywell

The connection between Alzheimer's and diabetes still requires more research to solidify. In the meantime, if you have diabetes and are concerned about your risk of developing Alzheimer's disease, talk with your physician about your best treatment options, which may include a healthy lifestyle and diet, exercise, and medication. 

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