Why is Dementia called Type 3 Diabetes?

February 05, 2025 • Read Time: 9 minutes

In today’s post, the relationship between insulin, diabetes, and dementia.

Why is Dementia called Type 3 Diabetes?

Have you heard anyone say “Type 3 diabetes”? While not an official medical term, the phrase started gaining traction about 20 years ago when researchers noticed similarities between the way the body functions in people with diabetes and the way the brain functions in those with Alzheimer’s ⚭. Since then the term of has gained popularity. When I started my own quest to understand my dad’s Alzheimer’s diagnosis, the concept of Type 3 diabetes was new to me. Seeing it pop up in dementia-related publications made me realize two things:

  1. None of my close friends or family had diabetes, and I was unfamiliar with the disease in general. I had NO idea what Type 3 diabetes meant.

  2. It sounded interesting. If there are similarities between the causes of dementia and diabetes, could treatments be similar as well?

I started reading NIH research papers hunting for answers. After a few hours, moving slowly and looking up a lot of medical jargon, I was able to get a better understanding of what Type 3 diabetes means.

I also found something that will take a few more weeks for me to fully understand. There is a long history of research around insulin treatment for dementia. I tried to write about it in this article, but realized that I needed more time to learn before I could explain it. So for now, just a summary of my limitless brain's understanding of the term Type 3 diabetes 🧐.

Type 1 & 2 - Diabetes Basics

Let’s start with the relationship between insulin and blood glucose, aka “blood sugar.” Glucose is the body’s primary energy source and mostly comes from carbohydrates in the food we eat. It floats around in our bloodstream until insulin, a hormone naturally created in your pancreas, get released. Insulin’s job is to tell our cells that it’s time to convert that glucose into energy. Our cells do this by pulling in glucose from the bloodstream and using it as fuel to carry out all of their various functions. Therefore, when everything in the body is working properly, an increase in insulin results in lower blood sugar.

⬆️ Insulin = ⬇️ Blood Sugar (glucose in your bloodstream)

This insulin/blood sugar relationship is impaired in people with diabetes because their bodies either can’t produce enough insulin or can’t use it effectively to communicate with cells. Instead of being used for energy production, glucose builds up in their bloodstream, putting their bodies into in a hyperglycemic state with abnormally high blood sugar levels.

Diabetes is diagnosed with a blood sugar test, something you can buy over the counter. If your fasting blood sugar level (after no food or drink for 8-12 hours) is less than 100 mg/dL, then you’re considered in the normal range. A fasting blood sugar level from 100 to 125 mg/dL is considered prediabetes. A result of of 126 mg/dL or higher on two separate tests, can result in a diabetes diagnosis.

There are currently only two types of diagnosable diabetes: Type 1 and Type 2.

Type 1

Makes up 10% of diabetes cases. Typically diagnosed in children, often between ages 4 and 6. Generally considered to be genetic or autoimmune, and is defined by a body producing little or no insulin.

Type 2

Makes up 90% of diabetes cases. Often referred to as adult-onset diabetes as it’s typically diagnosed in middle-aged adults. Risk factors that increase the likelihood of developing Type 2 diabetes include excess body fat, physical inactivity, poor diet, family history and age.

There is no known cure for either type and treatments vary

People with Type 1 always require insulin injections since they don’t produce enough of their own. People with Type 2 may also need insulin injections, but many can manage their diabetes with healthy lifestyle choices and oral medication.

Why is diabetes so dangerous? Because people with diabetes cannot naturally make or use insulin properly, they are at risk of high blood sugar levels. High blood sugar is okay if it happens infrequently. But when a body is constantly left in a hyperglycemic state, the excess glucose can seriously damage nerves and blood vessels. Because of this damage, people with diabetes often suffer from impaired blood flow that can lead to limb amputation and to the permanent injury of vital organs. Not good!

“Type 3” - The Diabetes / Dementia Relationship

So how does this all relate to dementia? When people develop diabetes as adults (Type 2), it’s often because they’re bodies stop using insulin effectively. Their bodies are in a hyperglycemic state for an extended period of time, during which the pancreas tries to crank out enough insulin to deal with all of that excess blood sugar. Eventually, the cells just stop effectively responding to the insulin. This condition is called insulin resistance.

When someone has insulin resistance, their blood sugar remains high because there is a breakdown in the communication between the insulin and cells. Since glucose stays in the blood, cells don’t get the energy they need to perform whatever work it is they have to do. When this malfunction happens in the body, we call it diabetes. But if you apply it to the brain specifically? That is where the term “Type 3 Diabetes” comes from.

The brain only makes up about 2% of our body weight yet it uses ~20% of total blood glucose, making it the highest energy consuming organ in the body 🔗. If it stops being able to intake that glucose, due to insulin resistance, the brain can’t operate optimally. A 2023 NIH article goes into great detail how insulin resistance could be a major cause of dementia, stating the following:

“insulin resistance reduces the supply of glucose, which is the main energy source of the brain…When the main energy source is insufficient,…the volume of white matter in the brain is reduced, which weakens the connections between brain regions. Insulin resistance is pointed out as one of the direct causes of dementia, in that diabetes and AD are so similar that dementia is the so-called type 3 diabetes.” 🔗

Researchers have been digging into this relationship for 20+ years. Here are some additional findings of studies that support the use of the term “Type 3 diabetes.”

  • People with insulin resistance are three times more likely to develop Alzheimer’s disease and other dementias.

  • 2013 study - tracked blood glucose levels of more than 2000 adults for 7 years and found that higher blood sugar was associated with higher risk of dementia, including Alzheimer’s.

  • 2021 study that found that the earlier in life Type 2 diabetes is diagnosed, the greater the risk of developing Alzheimer’s.

Similar Treatments

The concept of “Type 3 diabetes” revolves around that idea that what’s happening in the body of someone with diabetes looks similar to what’s happening in the brain of someone with dementia, specifically Alzheimer’s disease. In the body, insulin resistance often leads to diabetes and physical decline. In the brain, insulin resistance leads to dementia and cognitive decline. The science is not fully understood yet despite a lot of research and money going into diabetes and dementia. There are no known cures for either at this point. However, the current treatments and prevention techniques are similar.

  • There is ongoing research exploring (but not yet proving) if dementia and diabetes can be treated with the same drugs such as insulin, Metformin, and GLP-1s. These drugs are all currently used to treat diabetes. Additional reading if you want to dig in more.

  • People can manage their Type 2 diabetes symptoms by making the same healthy lifestyle choices that are also suggested to people for slowing down/managing symptoms of dementia and Alzhimers. This includes physical exercise and a healthy diet. In fact, people have been known to actually reverse insulin resistance with by making these choices. Insulin resistance The Lancet - 12 modifiable factors to preventing Alzheimer’s are similar to those to preventing or managing diabetes If caught early, dementia and diabetes can both be held at bay for a time by healthy lifestyle choices and those recommended lifestyle choices are almost identical.

Well, I hope that explains it. While the term “Type 3 diabetes” is eye-catching, it’s important to remember that it’s not yet an official medical diagnosis. It’s more of a theory, but one that is being explored in detail and with interesting implications to potential treatments.

That’s all for now! B

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