Could 'Type 3' diabetes harm your brain? What your blood sugar levels mean for Alzheimer’s risk

For years, diabetes has been seen as a condition that affects the body — blood sugar, insulin, weight, and long-term heart health. But new research is pointing to a surprising connection: the brain. Some scientists have even given this overlap a provocative nickname: 'Type 3 diabetes.'

It’s not an official medical diagnosis, but the term reflects growing evidence that insulin resistance in the brain may play a role in Alzheimer’s disease. And, this link is too important to ignore.

Hala Zakaria, Senior Research Coordinator at GluCare.Health by meta[bolic], explains: “Type 3 diabetes’ is an informal, research-driven term describing Alzheimer’s disease as a result of brain-specific insulin resistance. It does not describe classic diabetes affecting blood glucose.”

The distinction matters. Type 1 diabetes is an autoimmune attack on the pancreas, Type 2 stems from systemic insulin resistance, and 'Type 3' points to a brain that can’t respond to insulin properly, which may contribute to cognitive decline. Neurologist Dr. Bobby Jose from Medcare Royal Specialty Hospital sums it up: “‘Type 3 diabetes’ emphasises the idea that disrupted insulin signaling in the brain may contribute to Alzheimer’s pathology.”

The link between diabetes and Alzheimer’s is no longer just speculation. In fact, as Zakaria explains, meta-analyses show 56 per cent higher risk of Alzheimer's and 73 per cent higher risk of dementia in patients with Diabetes compared to non-diabetics.

But not everyone with diabetes faces the same risk. People with long-standing disease, poor glycemic control, obesity, vascular issues, or insulin resistance are particularly vulnerable. Zakaria adds, “The more uncontrolled one is, the higher the risk."

A 2012 study in the Journal of Clinical Investigation showed that people with Alzheimer’s disease have brain insulin resistance, especially in the hippocampus, even if they don’t have diabetes. This resistance is linked to IRS-1 dysfunction and reduced IGF-1 signaling, which interfere with how brain cells use energy. Higher levels of these markers were associated with worse memory and cognitive decline, suggesting insulin resistance in the brain may contribute directly to Alzheimer’s progression.

The brain runs on glucose. When insulin — the hormone that helps cells use glucose — isn’t working properly, nerve cells struggle. As both the experts explain: Brain insulin resistance refers to impaired insulin signaling specifically within cells in the brain. This mainly impacts how brain cells use energy, how we think and remember, and processes that contribute to nerve cell damage.”

Even when blood sugar is normal, studies show people with Alzheimer’s have reduced insulin sensitivity in the brain. The result: Cells struggle to use glucose efficiently, leading to energy shortages, weaker connections between neurons, and trouble forming new memories. That energy deficit also triggers inflammation and abnormal protein buildup — hallmarks of Alzheimer’s. Dr. Jose echoes this: “Nerve cells struggle to communicate, inflammation increases, and toxic proteins accumulate more easily.”

While diabetes hasn’t been proven to cause Alzheimer’s, the correlation is strong enough that experts recommend proactive measures. Zakaria says:
“Early and effective diabetes management has definite potential in reducing overall cognitive decline.” Moreover, large studies show that poor glycemic control significantly increases dementia risk.

Yet, there’s a glaring gap: “There are currently no formal guidelines recommending routine Alzheimer’s screening in people with diabetes,” she points out.

New blood tests measuring a protein called p-Tau217, such as GluCare.Health plasma p-Tau217 test, are emerging as some of the earliest indicators of Alzheimer’s disease. Moreover, research from the National Institutes of Health shows these tests can be nearly as accurate as spinal fluid tests and brain scans, with diagnostic performance around 92–97 per cent.

What is p-Tau217?

It’s a specific form of the tau protein in the brain. Tau normally helps support and stabilise nerve cells, but in Alzheimer’s, it becomes abnormal and 'phosphorylated,' forming clumps that interfere with communication and contribute to memory loss.

The p-Tau217 blood test measures this protein in the bloodstream — a far easier, less invasive alternative to spinal fluid tests or PET scans. Some research even shows elevated p-Tau217 levels up to 20 years before symptoms appear. Doctors often use this to flag high-risk individuals, then confirm findings with imaging or spinal fluid tests, according to a study titled Plasma Phosphorylated Tau 217 to Identify Preclinical Alzheimer Disease, in JAMA Network.

Another tool is the p-Tau217 to β-amyloid ratio, used in tests like Lumipulse G, approved by the FDA for adults over 55 with memory symptoms.

This test looks at both tau changes and amyloid buildup, the two main Alzheimer’s markers. In fact, it predicts Alzheimer’s with about 92 per cent positive and 97 per cent negative accuracy compared with PET or spinal fluid tests, offering a much less invasive option.

Currently, however, these tests are approved only for people with symptoms, though research hints at future preclinical use.

Both experts say yes. Zakaria stresses: “Periodic cognitive assessment as part of clinical care is advisable,” while Dr. Jose adds, “It is generally better to monitor cognitive health regularly, because diabetes, particularly poorly controlled diabetes, significantly increases the risk.”

Research is promising but still early. Dr. Jose notes, “Insulin therapy, GLP-1 agonists, and metformin have been studied. While the evidence is promising, these treatments are not yet approved specifically for Alzheimer’s.”

Zakaria echoes this: managing diabetes through medication and lifestyle changes may lower Alzheimer’s risk, but no trial has yet shown a direct prevention effect.

Diabetes doesn’t cause Alzheimer’s — but it does make the brain more vulnerable. Experts argue that maintaining good metabolic health, keeping blood sugar, blood pressure, and weight under control, remains one of the most important ways to protect long-term brain health.