Research ties diabetes to dementia risk and brain changes
The Conversation says evidence links diabetes, insulin resistance and blood-vessel damage to dementia, while some diabetes drugs may reduce risk.
By Priya Raghavan · Science Reporter
3 min read
Diabetes and dementia appear to be connected through blood sugar control, insulin signaling, blood-vessel injury and inflammation, according to a review published by The Conversation and republished by ScienceDaily. The findings matter because several diabetes treatments are now being studied for possible effects on brain aging and dementia risk.
Craig Beall and Natasha MacDonald wrote in The Conversation that people with diabetes are about 60% more likely to develop dementia than people without diabetes. They also cited evidence linking repeated episodes of low blood sugar with a 50% higher chance of cognitive decline.
How blood sugar may affect the brain
The Conversation said insulin resistance, the central problem in many cases of type 2 diabetes, does not only affect muscles and the liver. In Alzheimer’s disease, the same process may make it harder for brain cells to draw energy from glucose, contributing to cognitive problems.
The brain accounts for about 2% of body weight but uses roughly 20% of the body’s energy, according to The Conversation. In dementia, brain cells appear to lose some ability to use glucose efficiently, a pattern sometimes described unofficially as “type 3 diabetes.”
The relationship may also run in the other direction, Beall and MacDonald wrote. People with Alzheimer’s often have higher fasting blood glucose even without diabetes, while animal studies have found that Alzheimer’s-like brain changes can raise blood glucose levels.
The Conversation also pointed to APOE4, the strongest known genetic risk factor for Alzheimer’s. The authors wrote that the variant can reduce insulin sensitivity by trapping an insulin receptor inside cells, preventing it from working properly.
Blood vessels and inflammation
Diabetes can damage blood vessels in the eyes, kidneys and heart, and The Conversation said similar injury can affect the brain. High or fluctuating glucose levels may harm brain vessels, reduce blood flow and limit oxygen delivery.
Beall and MacDonald also wrote that diabetes can weaken the brain’s protective barrier, allowing harmful substances to enter and promoting inflammation. Reduced blood flow and inflammation in the brain are both strongly linked to dementia, according to the review.
Drug research expands
The Conversation said memantine, a drug used for moderate to severe Alzheimer’s symptoms, began as a diabetes treatment. It failed as a glucose-control drug, but later research found that it could help brain function.
Metformin, the widely used diabetes medicine, reaches the brain and may reduce brain inflammation, according to the review. Some studies cited by The Conversation suggest people with diabetes who use metformin have lower dementia risk, while people who stop taking it may see risk rise again; trials are also testing the drug in people without diabetes.
GLP-1 receptor agonists such as semaglutide, sold as Ozempic and Wegovy, lower blood glucose and support weight loss. The Conversation said records show lower dementia risk among people with diabetes using these medicines, and two major trials, Evoke and Evoke Plus, are testing oral semaglutide in people with mild cognitive impairment or early mild Alzheimer’s disease.
Researchers have also tested insulin delivered through the nose, a method intended to send insulin to the brain while limiting effects on blood sugar, according to The Conversation. Small studies suggest possible memory benefits or reduced brain shrinkage, but the authors said delivery remains inconsistent and long-term safety is not established.
The Conversation also cited emerging evidence that SGLT2 inhibitors, tablets that lower blood sugar by increasing sugar removal in urine, may reduce dementia risk in people with type 2 diabetes, including Alzheimer’s and vascular dementia. Beall and MacDonald wrote that researchers still need to determine whether these drugs lower only diabetes-related dementia risk or might also help people without diabetes.
This story draws on original reporting from ScienceDaily.