What is Type 3 diabetes? Understanding the diabetes-dementia link

You’ve likely heard of Type 1 and Type 2 diabetes, but you may not have heard of this third type. Type 3 diabetes is a term used by some researchers to refer to emerging data that shows a link between insulin resistance and dysfunction of a hormone called insulin-like growth factor (IGF-1), which may be a causal factor in Alzheimer’s disease. Here is what we know so far about the connection between blood sugar and dementia.

What is Type 3 diabetes?

Alzheimer’s disease should be classified as a type of diabetes, called Type 3 diabetes, proposed a 2008 study in the Journal of Diabetes Science and Technology.

“Their research proposed that problems with brain insulin and [insulin-like growth factor] IGF-1 signaling pathways could cause certain molecular abnormalities seen in Alzheimer’s disease,” says Yan Yan Sally Xie, MD, an endocrinologist at Northwell Health. 

The study’s hypothesis is that Alzheimer’s disease may be triggered by insulin resistance in brain cells. However, Type 3 diabetes is not an official diagnosis by any major health organizations or the American Diabetes Association. 

Although not recognized clinically, the term Type 3 diabetes (sometimes referred to as diabetes of the brain) is still used by some researchers to refer to a form of diabetes associated with Alzheimer’s disease, explains Ana Maria Kausel, MD, an endocrinologist and co-founder at Anzara Health.

The link between Alzheimer’s and diabetes 

Alzheimer’s disease is a type of dementia that affects cognitive function and is associated with multiple factors, including genetic propensities, environmental factors, lifestyle choices, severe head trauma, and a history of depression. 

Diabetes mellitus occurs when the body can’t effectively convert blood sugar energy, which causes blood glucose levels to be too high. There are four commonly accepted kinds of diabetes:

• Type 1 diabetes: A problem with the immune system prevents the pancreas from producing enough insulin.
• Type 2 diabetes: The body becomes unable to use insulin correctly or produce adequate insulin, and blood sugar levels become too high.
• Gestational diabetes: During pregnancy, the body cannot produce enough insulin or use insulin correctly, and blood sugar levels become too high.
• Prediabetes: A condition when blood sugar levels are higher than normal, but not high enough to be classified as Type 2 diabetes.

There is an established association between Type 2 diabetes and dementia: Type 2 diabetes, especially when uncontrolled or undiagnosed, can damage blood vessels in the brain, which can lead to cognitive decline, according to Dr. Xie. Type 2 diabetes can also cause systemic inflammation, which may damage the brain and cause cognitive impairment. 

Despite this connection, the scientific community is still trying to fully understand the causes of Alzheimer’s disease and its relationship to diabetes. Researchers suggest that Type 3 diabetes occurs when your brain stops responding well to insulin, which impacts memory and learning capabilities.

Causes and risk factors for Type 3 diabetes

People with Type 2 diabetes have a 45% to 60% higher risk of developing Alzheimer’s disease. Type 2 diabetes is also associated with a 60% higher risk of any type of dementia. Risk factors for Type 2 diabetes include:

• Prediabetes
• Obesity
• Family history of diabetes
• Limited physical activity
• Gestational diabetes

While the research on Type 3 diabetes is still preliminary, some of its possible causes include insulin resistance, genetics, and age.

Insulin resistance

A study published in 2020 in the International Journal of Molecular Sciences reported that Type 3 diabetes occurs when brain neurons become unresponsive to insulin, and because insulin is related to learning and memory, there is a likely link between insulin resistance and Alzheimer’s disease.

Genetics

In addition to insulin resistance, Dr. Kausel says that genetics may be at play. “Researchers at the Mayo Clinic found that a gene commonly found in Alzheimer’s patients (up to 50% of patients) called APOE4 is responsible for making the brain stop using insulin efficiently in the elderly,” she explains. “This same mechanism can happen in patients who have diabetes and later on develop Alzheimer’s since their overall metabolic health is driven by insulin resistance.”

Age

There isn’t research specifically on age and Type 3 diabetes. But in general, older adults have a higher risk of diabetes, dementia, and Alzheimer’s disease. According to the Alzheimer’s Association, age is the greatest factor leading to the development of Alzheimer’s disease, and the majority of cases are in people older than 65.

Type 3 diabetes symptoms 

Because so-called Type 3 diabetes manifests as Alzheimer’s disease, it’s assumed that symptoms of Type 3 diabetes resemble the symptoms of Alzheimer’s disease. Some of the most common symptoms of Alzheimer’s disease are:

• Memory loss
• More trouble remembering words compared to other people your age
• Decreased awareness of the space around you
• Challenges with reason, judgment, and decision-making
• Asking the same question multiple times
• Difficulty with daily living tasks, paying bills, and managing finances
• Going somewhere and not knowing how to get home
• Frequently losing things, especially in strange places (like leaving your keys in the microwave)
• Noticeable personality changes
• Mood changes

Diagnosing and treating Type 3 diabetes

Because there are currently no diagnostic criteria for Type 3 diabetes, it can’t be formally diagnosed—but Alzheimer’s disease is diagnosed based on medical history, a neurological exam, and cognitive tests.

Likewise, there is no established treatment protocol for Type 3 diabetes as it’s still a developing diagnosis. Researchers from the Mayo Clinic have been testing intranasal insulin spray, which they hope will help Alzheimer’s patients whose disease is related to insulin resistance. 

There are, however, established treatments for diabetes and Alzheimer’s disease. Your healthcare provider may recommend medication as well as lifestyle changes such as treating insulin resistance with diet and exercise. 

Although there is no research on whether Type 3 diabetes can be reversed, insulin resistance can be. “Weight loss and a diet based on non-processed carbohydrates and low in sugar is key,” Dr. Kausel says. 

Preventing Type 3 diabetes

Alzheimer’s disease and diabetes have multiple causes, some of which are out of your control, such as age and family history. However, half of your risk of developing dementia and Alzheimer’s disease is based on risk factors you can control—namely, dietary and exercise choices. Here are 8 tips recommended by the UCLA Longevity Center for preventing Type 2 diabetes and Alzheimer’s disease:

• Get regular aerobic exercise, which can help your body with glucose metabolism and with using insulin more efficiently.
• Add strength training into your routine, which increases insulin sensitivity and decreases high blood sugar levels.
• Stick to a diet low in added sugar and simple carbohydrates.
• Add in spices with anti-inflammatory and glucose-lowering properties, such as turmeric, cinnamon, and oregano.
• Aim to stay at a healthy weight.
• Keep your blood sugar at a healthy level, and take any medications your healthcare provider prescribes.
• Get plenty of rest.
• Take care to manage your stress.

As more research is performed, preventive and treatment measures may expand and adjust. If you’re at high risk for either health condition, work with your healthcare provider to create a personalized preventive care plan.