What’s the Link Between Type 2 Diabetes and Dementia?

Roughly 98 million American adults — more than 1 in 3 — have prediabetes, meaning their blood sugar levels are elevated but not high enough for a diagnosis of type 2 diabetes. If you’re one of them, your doctor has probably encouraged you to keep your blood sugar levels in check to avoid progression to type 2 diabetes.

Here’s why: Preventing type 2 diabetes protects you from the serious complications of the disease, like blindness and nerve damage. And many of the steps to prevention may also benefit your brain.

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“Diabetes and elevated plasma glucose levels are among the strongest and most consistently identified risk factors for cognitive decline and dementia,” according to the World Health Organization's 2026 report. The Lancet Commission on dementia prevention includes diabetes as one of its 14 modifiable risk factors for dementia. In fact, so many studies have shown a link between dementia and high blood sugar that some call Alzheimer’s disease “type 3 diabetes.”

How does high blood sugar harm the brain?

High blood sugar can harm the brain in many ways. It can damage blood vessels in the brain that carry oxygen-rich blood, killing off brain cells and making it harder for the body to create new ones. That, in turn, can lead to problems with memory and thinking.

Too much glucose has also been implicated in the formation of the plaques and tangles of proteins in the brain that are the hallmark of Alzheimer’s disease, the most common form of dementia.

In a long-term study using brain scans of close to 433,000 dementia-free adults ages 40 to 69, those with diabetes or prediabetes showed higher risk of vascular dementia and stroke compared with those with normal blood sugar levels. Brain scans of almost 40,000 of the participants showed smaller gray matter and hippocampus volumes among those with prediabetes and diabetes. The results, published in the European Journal of Preventive Cardiology in 2026, suggest that even prediabetes is a problem for brain health.

High blood sugar can also trigger inflammation, potentially damaging brain cells and compromising brain function, per a research review published in Diabetologia in 2026.

What can you do?

Prediabetes and diabetes often don’t have symptoms. The two share risk factors, such as being overweight, being age 45 or older, being physically inactive, and having a parent or sibling with type 2 diabetes.

There are ways to protect yourself. In a 2024 report, the Lancet Commission noted that strategies to prevent or control diabetes, such as maintaining a healthy weight, can help you retain healthy brain function and may help prevent dementia. 

Other ways to lower your risk of diabetes, according to the Centers for Disease Control and Prevention, include:

• Eating a diet rich in whole fruits and vegetables, lean protein and whole grains
• Avoiding processed foods, sugary drinks and alcohol
• Getting regular physical activity

We make it easy with our 7-day prediabetes meal plan.