What Is Type 3 Diabetes?

Someone pricking their finger to test blood sugar levels
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You've likely heard of type 1 diabetes and type 2 diabetes, but have you heard of type 3 diabetes? Some researchers are now proposing that Alzheimer's disease, a type of progressive dementia that affects more than 5 million Americans, be classified as "type 3 diabetes." Strong links have been made between the two conditions, most notably that dementia may be triggered by a type of insulin resistance occurring specifically in the brain.

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.

However, classifying Alzheimer's as type 3 diabetes is still controversial, and many in the medical community have not yet recognized type 3 diabetes as a medical diagnosis. More research is required.

It's also important to note that type 3 diabetes should not be confused with type 3c diabetes mellitus (also called T3cDM or pancreatogenic diabetes), a secondary condition that may arise as a result of other pancreatic diseases, affecting the function of the pancreas.

The Connection Between Alzheimer's and Diabetes

The stats are staggering: Studies show that the risk of developing Alzheimer’s disease among people with diabetes is increased by 65% compared to those without diabetes. With such a strong link, recent research has focused on explaining the connection between the two diseases.

First, here's what we know about diabetes type 1 and 2:

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.

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

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.

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.

The term "type 3 diabetes" is used, therefore, in two circumstances: to describe an actual type of diabetes that only affects the brain, and to describe the progression of type 2 diabetes to Alzheimer's disease.

Type 3 Diabetes Symptoms

The symptoms of type 3 diabetes are essentially the symptoms of early dementia, which, according to the Alzheimer's Association, may include:

  • Difficulty completing once-familiar tasks, such as driving to the grocery store
  • Memory loss that disrupts your daily life
  • Challenges in planning or problem solving
  • Confusion with time or place
  • Trouble understanding visual images or spatial relationships, such as difficulty with reading or balance
  • Having trouble joining or following conversations or speaking/writing
  • Frequently misplacing things and being unable to retrace your steps
  • Mood or personality changes

Symptoms of type 2 diabetes may include increased thirst, fatigue, hunger, frequent urination, dizziness, and blurred vision.

Causes

For decades, researchers have attempted to determine the specific cause of 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.

However, we do now know 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.

Risk Factors

The primary risk factor for developing type 3 diabetes is having type 2 diabetes. The risk factors for developing type 2 diabetes include:

  • A family history of diabetes or metabolic syndrome
  • Age over 45
  • High blood pressure (hypertension)
  • Overweight or obesity
  • Polycystic ovarian syndrome (PCOS)
  • Low physical activity

Diagnosis

While there's no dedicated test for type 3 diabetes yet, clinicians will typically look for signs of Alzheimer's and signs of diabetes.

To diagnose Alzheimer's, practitioners will typically:

  • Take a full medical history
  • Ask about your family history with regard to Alzheimer's/dementia
  • Perform a neurological examination
  • Perform neurophysiological testing
  • Recommend imaging studies, such as an MRI, which can give a better glimpse into how your brain is functioning, and to look for the hallmark amyloid plaques consistent with Alzheimer's.

If you have symptoms of type 2 diabetes, your physician may also request that you do a fasting or random glucose test and a hemoglobin A1c (Hb A1c) test to see how well your blood sugar is being controlled.

Treatment

If you have been diagnosed with both type 2 diabetes and Alzheimer's, your physician may recommend a diabetes treatment protocol to help get your blood sugar levels under control–which will hopefully reduce the potential damage to the brain.

Standard treatment for type 2 diabetes includes:

  • Lifestyle modifications such as weight loss, dietary changes, and exercise
  • Various drugs therapies including sulfonylureas, glucagon-like peptides, biguanides such as metformin, and others
  • Supplemental insulin, generally used only when lifestyle changes and other first-line drugs aren't effective
  • Frequent blood sugar monitoring and Hb A1c testing

There is potential that diabetes medications such as metformin and glucagon-like peptides may be helpful in preventing the progression of Alzheimer's. In both animal and human studies, research has demonstrated that medications improving insulin sensitivity can protect against the structural abnormalities that develop in Alzheimer's disease, improve the brain's ability to metabolize glucose, and demonstrate an improvement in the brain's cognitive functioning in some cases. However, more research needs to be done.

Specific pharmaceutical treatment for Alzheimer's has proven elusive, however. While there are several prescription medications that are designed to treat Alzheimer's symptoms, their true effectiveness remains in question.

Many patients with Alzheimer's have been found to have low levels of acetylcholine.  Medications known as cholinesterase inhibitors, for example, donepezil (Aricept), galantamine (Razadyne), or rivastigmine (Exelon), may help by protecting the amount of acetylcholine in the brain.

Memantine (Namenda), an NMDA-receptor antagonist, has been shown to marginally reduce the progression of the disease, and is usually prescribed alongside a cholinesterase inhibitor.

Behavioral symptoms such as depression, common in early stages of Alzheimer's, are typically treated with selective serotonin reuptake inhibitors (SSRIs).

Alzheimer's medications are generally trialed first for eight weeks, then reviewed to determine if there's any benefit.

Ultimately, Alzheimer's treatment is focused largely on prevention.

Prevention

There's a great amount of crossover between diabetes and Alzheimer's prevention, including following a healthy diet and increasing your physical activity.

To reduce your risk of developing Alzheimer's disease specifically, follow these four pillars:

  • Follow a diet like the Mediterranean Diet, which is rich in whole foods and low in processed, refined foods, and take a high-potency supplement.
  • Seek out physical exercise (ideally 150 minutes of cardio and strength training each week), and mental exercise (reading, creating art, doing crossword puzzles).
  • Try yoga and meditation to reduce chronic stress.
  • Enhance your psychological well-being by socializing with others and providing service in your community.

There have been numerous studies outlining how lifestyle changes can improve glucose control in patients with type 2 diabetes. In addition to the four pillars above, diabetes prevention can incorporate:

  • Losing 5 to 10% of your body weight to help restore insulin sensitivity.
  • Quitting smoking to reduce the stress on your organs.
  • Getting adequate sleep nightly to reduce the effects of chronic stress and improve glucose absorption.

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, stress relief, and medication. 

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