When most people think of diabetes, they picture high blood sugar, insulin injections, and strict diets. It is a condition tied to how the body uses sugar, which is mainly linked to the pancreas.
On the other hand, Alzheimer’s disease brings up images of memory loss, confusion, and a slow decline in thinking skills, which is clearly a brain problem.
These two illnesses seem very different, as one affects metabolism, and the other affects the brain. But recent research suggests something surprising: Alzheimer’s might actually be a form of diabetes, sometimes called ‘Type 3 diabetes.’
Though this idea was once doubted, more scientists are starting to accept it as they discover clear similarities between how diabetes and Alzheimer’s work. To understand this better, let’s look at what goes wrong in both conditions.
A quick look at diabetes
Diabetes is basically a problem with how the body uses glucose, the main fuel from the food we eat. For glucose to enter our cells and provide us with energy, we need insulin, that is a hormone that is like a key to unlock the cell’s door.
In T1D, the immune system attacks the insulin-making cells in the pancreas. Without insulin, glucose can not get into cells and instead builds up in the blood. This type is usually diagnosed in younger people and is considered an autoimmune disease.
In Type 2 diabetes, the body either does not make enough insulin or the cells stop responding to it, which is a problem known as insulin resistance.
The ‘key’ (insulin) is present, but the ‘lock’ (cell receptor) is not working right, and blood sugar rises. Type 2 diabetes is strongly tied to things like poor diet, lack of exercise, and obesity.
Alzheimer’s Disease: Not Just Memory Loss

Alzheimer’s is a disease that slowly destroys memory and thinking ability, and eventually makes it hard to carry out even basic tasks.
For years, scientists focused on two key features in the brains of people with Alzheimer’s: amyloid plaques and tau tangles.
Amyloid plaques are clumps of protein that form outside brain cells, while tau tangles build up inside them. These disruptions block communication between brain cells and eventually kill them.
The Brain Needs Sugar, too
Now, here is where things get interesting. Insulin does not just help muscles and fat use sugar, as it is also important in the brain, too.
Although the brain is only about 2% of our body weight, it uses around 20% of our glucose [ref]. Brain cells (neurons) need insulin to help absorb glucose and use it for energy. But insulin also helps in other brain functions:
Memory and learning: Insulin supports synaptic plasticity, meaning how neurons form and adjust connections. This process is key for learning and memory.
Neuron survival: Insulin acts like a growth signal in the brain, helping neurons stay alive and healthy.
Cleaning up waste: There is an enzyme called insulin-degrading enzyme (IDE) that breaks down insulin, and it also breaks down amyloid beta. But if insulin levels are too high, IDE might be too busy handling insulin to clean up amyloid, allowing plaques to build up.

When the Brain Becomes Insulin Resistant
This leads us to the heart of the ‘Type 3 diabetes’ idea. Many people with Alzheimer’s show signs that their brain is insulin resistant [ref]. In other words, even if insulin is present in the brain, the neurons can not use it properly.
- Brain cells cannot get the glucose they need, which then leads to memory loss and slower thinking.
- Insulin resistance causes low-level inflammation in the brain, which damages neurons over time.
- Insulin problems may directly lead to the buildup of amyloid plaques and tau tangles, either because of less IDE activity or disrupted cell signaling.
One of the strongest pieces of evidence linking Alzheimer’s to insulin problems is that people with Type 2 diabetes are much more likely to develop Alzheimer’s, up to twice the risk.
Long-term high blood sugar and insulin resistance damage the brain’s energy system, making it more vulnerable to Alzheimer’s. [ref]
Why is Alzheimer’s Called Type 3 Diabetes?
So, is Alzheimer’s actually a type of diabetes? Technically, ‘Type 3 diabetes’ is not a formal diagnosis.
It is a way of describing the growing belief that Alzheimer’s is partly a metabolic disorder, not just a brain problem, but a result of the brain’s inability to use insulin and glucose properly.
This new way of thinking changes how we approach Alzheimer’s
New treatment options: If insulin resistance is involved, then drugs used to treat diabetes, especially those that improve insulin sensitivity, might help Alzheimer’s patients. Researchers are testing diabetes medicines to see if they can slow down or improve brain function in these patients.
Lifestyle and prevention: Since Alzheimer’s shares risk factors with Type 2 diabetes, preventing or managing diabetes may also protect the brain. Eating a healthy diet, staying active, keeping weight in check, and managing stress may lower the risk of developing Alzheimer’s.
Whole-body health: This theory reminds us that the brain does not work in isolation. Problems like insulin resistance affect the whole body, including the brain. Protecting your metabolic health might be one of the best ways to protect your mind.
Final thoughts
Although ‘Type 3 diabetes’ is not an official term, the growing evidence shows a powerful link between insulin resistance and brain decline.
Viewing Alzheimer’s through the lens of metabolism gives us a deeper understanding of how the disease develops and opens up new paths for treatment and prevention.
If we start seeing the brain as an energy-hungry organ that depends on good insulin function, we may be better equipped to protect it as we age.
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