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Type 3 diabetes: Symptoms, causes and treatments

Image shows a scientist adding a sample to a test tube in front of computer monitor showing images of brain scans
(Image credit: Getty)

While most of us are familiar with type 1 and type 2 diabetes, you may not have come across the term ‘type 3 diabetes’ before. First things first, this is not to be confused with type 3c diabetes, which is something else entirely. It is, however, related to insulin resistance in the brain. 

Being diagnosed as insulin resistant generally means that someone is either prediabetic or has type 2 diabetes (opens in new tab). But scientists have proposed that it can also result in the brain’s neurons lacking glucose, which is needed for proper function, and this can lead to symptoms of Alzheimer's disease. 

While type 3 diabetes is not an officially recognized health condition, in 2008 Dr Suzanne de la Monte and Dr Jack Wands of Brown University put forward a proposal that Alzheimer’s disease could be termed ‘type 3 diabetes’ due to its strong links with insulin resistance in the Journal of Diabetes Science and Technology (opens in new tab). Insulin resistance may be a leading cause of dementia, as this glucose metabolism deficiency in the brain contributes to symptoms such as loss of memory, decrease in judgment and reasoning skills.

THIS ARTICLE HAS BEEN MEDICALLY REVIEWED BY
Dr. Rebecca Breslow
THIS ARTICLE HAS BEEN MEDICALLY REVIEWED BY
Dr. Rebecca Breslow

Dr. Rebecca Breslow is a physician, researcher, and writer.  A graduate of Yale University, she did her medical training at Harvard Medical School, Brigham and Women’s Hospital, and Boston Children’s Hospital.  She was a practicing physician in academic medicine for 17 years, during which time she authored numerous publications for academic and lay audiences.  Currently, she focuses on freelance medical writing and editing to help make medical, health, and wellness information accessible to a broad audience.  

What is type 3 diabetes?

Type 3 diabetes is not a medically recognised term and is not something doctors use for diagnostic purposes. However, insulin resistance and decreased insulin signaling in the brain may play a role in the development of Alzheimer's disease. Not to mention, the risk of developing Alzheimer's disease is significantly higher in those with type 2 diabetes. As such, the term ‘type 3 diabetes’ has been colloquially used by some in the field to illustrate these links. A study in the Lancet journal of Neurology (opens in new tab) links diabetes with declining brain health and indicates that treatments that restore cerebral insulin function may offer therapeutic benefits to those with Alzheimer's disease. 

Dr. William H Frey II PhD., an Alzheimer's research specialist at the Health Partners Center for Memory and Aging (opens in new tab), also explains that the disease causes cognitive decline in patients. “Alzheimer's is a degenerative brain disease that accounts for more than 60% of the cases of dementia,” he tells Live Science. “It is characterized by memory loss, especially short-term or recent memories, cognitive decline and changes in behavior, all of which get progressively worse over time.” 

Dr Tariq Mahmood, a medical doctor with 30 years experience, and the medical director at Concepto Diagnostics (opens in new tab), adds: “Type 3 diabetes isn’t an officially recognized health condition and isn’t used for diagnostic purposes. It differs from type 1 diabetes (opens in new tab) and type 2 diabetes, which cause blood sugar levels to become too high due to issues with a hormone called insulin. Some scientists hypothesize that insulin dysregulation in the brain causes dementia and use type 3 diabetes as a term to describe Alzheimer’s disease – a progressive neurological condition which is the most common cause of dementia.” 

Type 3 diabetes: Symptoms and diagnosis

Mahmood explains that while ‘type 3 diabetes’ is not an official diagnosis, doctors can diagnose Alzheimer’s disease, which affects multiple brain functions gradually over the course of many years. “Minor memory problems are usually the first sign,” he says. “More specific symptoms can include confusion, difficulty planning, disorientation, getting lost and personality changes.”

Early to moderate symptoms of Alzheimer's include: 

  • Lack of judgment
  • Memory loss
  • Confusion
  • Agitation/anxiety
  • Problems with reading, writing, numbers
  • Difficulty recognising family and friends
  • Disorganized thoughts
  • Lack of impulse control

These symptoms usually develop to a point that patients cannot swallow, lose bowel control and eventually pass away. Often people with Alzheimer's die from aspiration pneumonia. This develops when problems swallowing cause food or liquids to pass into the lungs instead of air due to problems with swallowing, as is stated by the National Institute of Aging (opens in new tab). Dr Frey tells us that Alzheimer’s is best diagnosed by a neurologist familiar with neurodegenerative memory disorders. “Diagnostic procedures may involve taking a complete history, blood tests, brain imaging, neuropsychological testing, etc. to help rule out other disorders that may produce somewhat similar symptoms,” he says.

What causes type 3 diabetes?

A review on insulin resistance in Frontiers in Neuroscience (opens in new tab) indicates that insulin is involved in multiple common conditions, such as obesity, dementia and diabetes. The review discusses how antidiabetic medications may be used to prevent and/or treat Alzheimer’s dementia, along with addressing stress, life events and other environmental challenges. 

Mahmood tells us that while the science is unclear on the specific cause of Alzeimer’s disease, a combination of factors may be at play. “It’s widely believed that age-related neurological changes combined with genetic, environmental, and lifestyle factors can contribute toward it,” he says. “Age is the most important known risk factor for Alzheimer’s disease due to, among other things, atrophy in parts of the brain. Atrophy is the loss of brain tissue, meaning it can shrink, thin or be outright lost."

Nerve cells affected by Alzheimer's disease

(Image credit: Getty Images)

Dr Frey explains that general aging is not the only risk factor associated with the development of Alzheimer's disease. “Aging is the major risk factor for Alzheimer's disease, but Alzheimer's is not a normal part of aging,” he says. “A family history of Alzheimer's and genetic changes can also increase the risk, but individuals without a family history of the disease can still get it. A history of moderate traumatic brain injury can also significantly increase the risk for developing Alzheimer's disease. 

“Finally, type 2 diabetes doubles the risk for developing Alzheimer's disease. This is likely due to the fact that in both diabetes and Alzheimer's disease, there is a deficiency of insulin signaling.” 

He goes on to explain that in Alzheimer's disease, the insulin signaling deficiency leads to a loss of brain cell energy. Without sufficient insulin signaling, blood sugar is not taken into brain cells and metabolized normally. 

“Loss of brain cell energy means that the brain can no longer carry out memory and cognitive functions normally and also can not produce the parts of brain cells needed to replace those that wear out over time leading to degeneration of the brain itself.”

Unhealthy lifestyles, including lack of exercise, poor diet and lack of sleep, likely also increase the risk for Alzheimer's disease, he says.

Treatment

TREATMENT

Dr Frey’s research has been pioneering in the area of insulin resistance and Alzheimer's. In 2022, in a study in Pharmaceuticals (opens in new tab), Frey and colleagues studied biomarker uptake in brain regions implicated in the faulty uptake and metabolism of blood sugar in Alzheimer’s patients. Studies like these may identify new therapeutic modalities and help explain why emerging therapies, such as intranasal insulin (insulin administered up the nose) are effective in treating Alzheimer’s, Parkinson’s and other neurodegenerative disorders.

“Because insufficient insulin signaling contributes to loss of brain cell energy in individuals with Alzheimer's disease, [I] first proposed intranasal insulin as a treatment for Alzheimer's disease about 22 years ago,” he says. “Intranasal insulin targets and delivers insulin to the brain along the nerves involved in smell without altering the blood levels of insulin or blood sugar.”

image shows a brain scan to detect neurological decline

(Image credit: Getty Images)

Clinical trials have shown that intranasal insulin increases brain cell energy and improves memory in normal healthy adults, as well as those with mild cognitive impairment or Alzheimer's disease. However, it needs further development and testing to sufficiently demonstrate its safety and efficacy before it can be considered for regulatory approval and made available to patients.

Dr Mahmood tells us that while there is regrettably no cure for Alzheimer's disease, treatments for those with the condition are available. “There are medicines and treatments that can reduce symptoms on a temporary basis,” he says. “The two main medicines right now are acetylcholinesterase (AChE) inhibitors, which help nerve cells communicate with each other, and memantine, which blocks the effects of excessive glutamate – this is a neurotransmitter released by nerve cells which plays a major role in learning and memory.” 

For people who begin to show aggression or distress, antipsychotic medicines can also be prescribed. Other treatments, like cognitive rehabilitation and cognitive stimulation therapy, can help maintain memory and problem-solving skills.

Can you prevent type 3 diabetes?

A review in the Journal of Alzheimer's Disease (opens in new tab) indicates meditation may help prevent Alzheimer’s disease. It reduces allostatic load, which has been linked to the development of several cognitive disorders. The review found that 12 minutes of Kirtan Kriya meditation per day was seen to improve function of insulin and glucose regulatory genes. It was also indicated to improve sleep, decrease depression and anxiety, down-regulate inflammatory genes and  upregulate immune system (opens in new tab) genes. 

Dr Mahmood recommends general healthy living to reduce your risk too, although other risk factors are uncontrollable. “Unfortunately, there’s no way to prevent Alzheimer’s disease at the moment,” he says. “Living a healthy lifestyle might lessen your risk, but age-related neurological changes and genetic factors are impossible to work around. Cardiovascular disease has been linked with an increased risk of Alzheimer's disease, so eating a balanced diet, making sure you get 150 minutes of exercise per week, limiting alcohol consumption and stopping smoking are all worthwhile.”

Our easy Mediterranean diet plan (opens in new tab) and 7-day plant-based diet meal plan (opens in new tab) have lots of ideas to help you to eat a more balanced diet.

Dr Frey agrees that general healthy living is a wise course of action to reduce your risk of  Alzheimer's disease. He also recommends protecting your head. “Maintaining a healthy lifestyle including regular physical activity, avoiding head injury by wearing your seatbelt while in vehicles and a helmet during sports, consuming a healthy diet and remaining socially active can all help to reduce your risk for Alzheimer's disease,” he says.

This article is for informational purposes only and is not meant to offer medical advice.

Lou Mudge
Health Writer

Lou Mudge is a health writer based in Bath, United Kingdom for Future PLC. She holds an undergraduate degree in creative writing from Bath Spa University, and her work has appeared in Live Science, Tom's Guide, Fit & Well, Coach, T3, and Tech Radar, among others. She regularly writes about health and fitness-related topics such as air quality, gut health, diet and nutrition and the impacts these things have on our lives. 

She has worked for the University of Bath on a chemistry research project and produced a short book in collaboration with the department of education at Bath Spa University. 

With contributions from