Type 3 diabetes is a term used by some researchers to describe the theory that insulin resistance and insulin-like growth factor dysfunction in the brain may cause Alzheimer’s disease. More research needs to be done to understand the link between diabetes and Alzheimer’s disease.

Some research studies have suggested that Alzheimer’s disease should also be classified as a type of diabetes, called type 3 diabetes. However, type 3 diabetes is not currently an official medical term. It is not recognized by national health organizations or the American Diabetes Association.

Types of diabetes

Diabetes mellitus (also called DM or diabetes for short) is a health condition where your body has difficulty converting sugar to energy. Typically, we think of three kinds of diabetes:

  • Type 1 diabetes (T1D) is a chronic health condition in which your body’s endocrine part of the pancreas doesn’t produce enough insulin, and your blood sugar (glucose) level becomes too high.
  • Type 2 diabetes (T2D) is a chronic condition in which your body develops insulin resistance, causing your blood sugar level to become too high.
  • Gestational diabetes (GDM) occurs during pregnancy if the body cannot produce the insulin it needs and your blood sugar level becomes too high.
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This “type 3 diabetes” is a term proposed to describe the hypothesis that Alzheimer’s disease is caused by a type of insulin resistance and insulin-like growth factor dysfunction that occurs specifically in the brain.

This condition also has been used by some to describe people who have T2D and also receive a diagnosis of Alzheimer’s disease. The classification of type 3 diabetes is highly controversial, and it’s not widely accepted by the medical community as a clinical diagnosis.

Another classification of diabetes includes type 3c diabetes mellitus (also called T3cDM, pancreatogenic diabetes, and type 3c diabetes). This type of diabetes develops due to conditions that affect the pancreas. Despite having a similar name, this is a separate condition.

Type 3c diabetes mellitus

T3cDM occurs when the exocrine pancreas glands become damaged and cause damage to the endocrine pancreas glands. Beta-islet cells in endocrine pancreas tissue produce and secret insulin.

Causes that may lead to T3cDM can include:

  • chronic pancreatitis
  • cystic fibrosis
  • exocrine pancreatic cancer
  • previous pancreatic surgery
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Keep reading to find out what we know and what we don’t know about “type 3 diabetes.”

Researchers have examined a possible link between diabetes and the development of Alzheimer’s disease. Some suggest that Alzheimer’s may be triggered by insulin resistance in your brain.

This claim has some science behind it, but it’s a bit of an oversimplification.

Over time, untreated diabetes can cause damage to your blood vessels, including vessels in your brain. Many people who have T2D don’t know that they have the condition, which may delay diagnosis and treatment.

Therefore, those with T2D, especially undiagnosed diabetes, have a higher risk of this kind of damage.

Diabetes may also cause chemical imbalances in your brain, contributing to Alzheimer’s. Also, high blood sugar levels lead to inflammation, which may damage brain cells.

For these reasons, diabetes is considered a risk factor for vascular dementia. Vascular dementia is a stand-alone diagnosis with symptoms of its own. It can also be a warning sign of what will develop into an overlap with Alzheimer’s disease.

The science of this process is still uncertain. For now, what’s been established is that there are cases of Alzheimer’s disease and other forms of dementia that don’t have any demonstrated link to insulin resistance.

Scientists are still trying to understand Alzheimer’s disease, its causes, and its relationship to diabetes.

According to a 2022 review of research, people who have T2D may be up to 45% to 90% more likely to develop Alzheimer’s disease or another type of dementia, such as vascular dementia.

This study from 2016 involved more than 100,000 people living with dementia. It showed that females with T2D had a higher probability of developing vascular dementia than males.

Risk factors for T2D can include:

The symptoms of the proposed type 3 diabetes condition may include symptoms of dementia, such as those seen in early Alzheimer’s disease.

According to the Alzheimer’s Association, these symptoms can include:

  • memory loss that affects daily living and social interactions
  • difficulty completing familiar tasks
  • misplacing things often
  • decreased ability to make judgments based on information
  • sudden changes in personality or demeanor

There’s no specific test for type 3 diabetes, as it is not an official diagnosis. Alzheimer’s disease is diagnosed based on:

  • a neurological examination
  • medical history
  • neurophysiological testing

A healthcare professional will ask several questions about your family history and symptoms.

Imaging studies, such as MRI and CT scans of the head, may give a doctor a picture of how your brain is working. Cerebrospinal fluid testing can also look for indicators of Alzheimer’s.

If you have symptoms of T2D and Alzheimer’s but do not have either diagnosis, a doctor may order a fasting blood sugar test and a hemoglobin A1c test.

If you do have T2D, it’s important that you begin treatment for it immediately. Treating T2D could minimize damage to your body, including your brain, and slow the progression of Alzheimer’s or dementia.

There’s no one treatment for type 3 diabetes, as it is not an official diagnosis.

There are separate treatment options for people who have:

  • prediabetes
  • T2D
  • Alzheimer’s disease

A doctor may recommend lifestyle measures, such as diet and exercise.

A doctor may also recommend certain lifestyle measures that may include:

  • Managing weight: Doctors may recommend weight loss for some people with diabetes. If you are overweight, a doctor may recommend methods to help you lose around 7% of your body mass. This can help stop organ damage caused by high blood sugar and may prevent the progression of prediabetes to T2D, according to the National Institute of Diabetes and Digestive and Kidney Diseases.
  • Balancing diet: A diet low in fat and rich in fruits and vegetables can help improve symptoms.
  • Quitting smoking if you smoke: Avoiding smoking may help you manage your condition.

If you have T2D and Alzheimer’s, managing diabetes may also help slow the progression of dementia.

Researchers are investigating a possible link between metformin, a diabetes medication, and Alzheimer’s disease.

Some research suggests that the drug may have a protective effect against Alzheimer’s disease while other research suggests metformin may increase a person’s risk for Alzheimer’s disease. Additional studies are needed to understand the relationship between this drug and neurodegenerative disease.

Medications for Alzheimer’s disease

Prescription medications may treat cognitive symptoms of dementia, but there’s uncertainty about whether they have a noticeable impact on the symptoms of Alzheimer’s disease. Medications prescribed to people with Alzheimer’s disease can include:

  • anti-amyloid antibody intravenous infusion therapy, such as aducanumab (Aduhelm) and lecanemab (Leqembi), which may remove beta-amyloid from the brain to reduce cognitive and functional degeneration in people in the early stages of Alzheimer’s disease
  • acetylcholinesterase inhibitors, such as donepezil (Aricept), galantamine (Razadyne), or rivastigmine (Exelon), which may improve the way that your body’s cells communicate with one another
  • memantine (Namenda), an NMDA-receptor antagonist, may also help reduce symptoms and slow the progression of Alzheimer’s disease

Doctors may treat symptoms of Alzheimer’s disease, like mood changes and depression, with psychotropic drugs. Antidepressants and anti-anxiety medications are part of treatment in some cases.

Some people may need antipsychotic therapy later in the disease course.

Type 3 diabetes is a way of describing Alzheimer’s that may occur due to insulin resistance inside the brain.

Your outlook can vary according to several factors, including how well your diabetes is managed and the severity of your dementia.

If diabetes is being treated, some researchers who promote the diagnosis of type 3 diabetes suggest that you may be able to slow the progression of Alzheimer’s or vascular dementia. But the evidence is uncertain.

Your outlook may also vary based on where you are in the Alzheimer’s disease progression. How quickly you received a diagnosis and started treatment for either condition can play a role. The sooner treatment begins, the better your outlook may be.

According to the Alzheimer’s Association, the average life expectancy for a person with Alzheimer’s is around 4 to 8 years from their diagnosis. But some people with Alzheimer’s can live as many as 20 years after diagnosis.

If you have T2D, managing your condition with medication and lifestyle measures may help prevent Alzheimer’s disease and other complications.

Some of the proven methods for managing T2D and minimizing organ damage include:

“Type 3 diabetes” is a term some researchers use to describe the theory that insulin resistance and insulin-like growth factor dysfunction in the brain may cause Alzheimer’s disease. More research is needed to understand the link between diabetes and Alzheimer’s disease.

People who have T2D may be more likely to develop Alzheimer’s disease.

Managing diabetes may help prevent or delay complications, including Alzheimer’s disease.