Diabetes and Dementia

Type 2 diabetes raises the risk of memory problems and dementia, and both high and low blood sugar can harm the brain; learn why, what the research says about treatment, and how to protect your brain.

Last reviewed: October 2026

Diabetes is usually discussed in terms of eyes, kidneys, feet and heart. But the brain is affected too. The Alzheimer's Society calls diabetes a confirmed risk factor for dementia, and the 2024 Lancet Commission includes it among 14 risk factors that people can change (see Reducing Dementia Risk: The 14 Risk Factors). Understanding the link can be a powerful reason to keep blood sugar in check.

Diabetes in brief

Your body turns food into glucose (blood sugar) for energy. A hormone called insulin helps glucose get into cells. In diabetes, the body doesn't make enough insulin, doesn't use it properly, or both, so too much glucose stays in the blood (NIA).

Type 1 diabetes: the body makes little or no insulin. It usually starts in childhood or young adulthood.
Type 2 diabetes: the body's cells don't use insulin properly (insulin resistance). It's the most common type and occurs most often in middle-aged and older adults.
Prediabetes: blood sugar is higher than normal but not yet diabetes. The NIA notes that millions of older Americans have it—and that healthy weight, exercise and regular checks can help prevent or delay type 2 diabetes.

Type 2 diabetes often develops slowly and may cause no symptoms for a long time, so testing matters.

Why the brain is so sensitive to blood sugar

The CDC calls the brain the body's most energy-hungry organ: it needs about half of all the sugar energy in the body to work properly. When blood sugar strays too far outside its normal range in either direction, the brain feels it.

High blood sugar

According to the CDC, frequent high blood sugar (hyperglycemia) damages the blood vessels that carry oxygen-rich blood to the brain. When brain cells get too little blood, they can die. Over time this can cause problems with memory and thinking and can lead to Vascular Dementia. Because the damage builds slowly, people often don't know their brain is being affected.

Low blood sugar

Low blood sugar (hypoglycemia)—below 70 mg/dL—can be dangerous, the CDC says. Symptoms can include feeling dizzy, shaky or irritable, and trouble walking or talking. Severe lows can cause fainting, seizures or coma. Some research links big dips in blood sugar to problems with depression, memory and attention. Some people have no warning symptoms, which is why regular checks matter.

What the research says

The Alzheimer's Society summarizes the evidence this way:

Type 2 diabetes increases dementia risk. A review combining 14 studies found higher dementia risk in people with diabetes.
Duration and severity matter. Risk rises the longer someone has diabetes and the more severe it is.
Type 1 diabetes: severe blood sugar highs and lows are linked with increased dementia risk.
It's a risk, not a destiny. Having diabetes does not mean a person will develop dementia.

Why might diabetes raise risk?

Researchers have several ideas, according to the Alzheimer's Society:

Shared risk factors. People with diabetes are more likely to have high blood pressure, high cholesterol and obesity, which also affect the brain. See Blood Pressure and the Brain and LDL Cholesterol and Dementia.
Insulin resistance in the brain. In both diabetes and Alzheimer's, brain cells may become resistant to insulin, which may contribute to the buildup of amyloid and tau proteins. (Alzheimer's is sometimes informally nicknamed "type 3 diabetes.") See Amyloid and Tau Explained.
Blood vessel damage, as the CDC describes above.

Does treating diabetes lower dementia risk?

This is less clear. The Alzheimer's Society notes that an analysis of 27 studies found several diabetes drugs were associated with lower dementia risk, but studies of metformin have had mixed results. It is hard to untangle the effects, because people taking more medicine often have more severe diabetes. Researchers are also studying whether newer diabetes and weight-loss drugs could help the brain; see GLP-1 Drugs and Alzheimer's Research.

What is not in doubt is that good diabetes control protects the eyes, kidneys, nerves and heart—and keeping blood sugar near target is what the CDC recommends for brain health.

Protecting your brain if you have diabetes

The CDC and NIA suggest:

Keep blood sugar close to your target range. Your doctor will set a personal target. Avoid both frequent highs and frequent lows.
Check your blood sugar as advised, especially if you take insulin or other medicines that can cause lows.
Follow a healthy eating plan rich in vegetables, fiber and fruit. See the The MIND Diet.
Be active most days of the week. Walking counts. See Exercise and the Brain.
Maintain a healthy weight.
Take medicines as prescribed, and tell your doctor about side effects or if you can't afford them.
Manage blood pressure and cholesterol, which the NIA recommends checking regularly.
Stop smoking if you smoke, and manage stress.

When memory and diabetes collide

The NIA notes that older adults with diabetes are at higher risk of depression and cognitive impairment, and that these problems can make diabetes self-care harder. Missed doses, double doses or skipped meals can lead to dangerous highs or lows.

If you help care for someone with diabetes and memory problems, some practical ideas to discuss with their care team:

Use a pill organizer or reminders, and consider supervising insulin or other medicines.
Learn the signs of low blood sugar and keep a fast-acting sugar source handy.
Ask the care team whether the treatment plan should be simplified. The NIA notes that care plans may change when health changes.

When to see a doctor

Talk with your doctor if you have symptoms of diabetes—such as feeling tired, being very thirsty or hungry, urinating often, or losing weight without trying (NIA)—or risk factors such as overweight, inactivity or a family history. If you have diabetes, the NIA says your doctor may screen you for depression or memory problems; mention any changes in memory, mood or attention, and report frequent low blood sugar episodes. Don't change your diabetes medicines on your own.

Sources

Not medical advice. This article is general information, not a diagnosis or treatment plan for any individual. Talk with a doctor about your situation.

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