Type 2 diabetes is linked to memory and thinking problems, and a new study suggests it's because the disease makes the brain age faster.
Looking at data from 20,000 middle-aged and older adults, researchers found that — consistent with past studies — people with type 2 diabetes generally did worse on tests of memory and thinking skills than those without diabetes.
Beyond that, MRI scans revealed differences in brain regions related to those skills: People with diabetes had more tissue shrinkage — akin to a 26% acceleration in normal brain aging.
It's well-known that brain tissue gradually shrinks as we age, with certain areas withering more and faster than others.
The new findings show that people with diabetes have atrophy in the same brain areas as other people their age, said senior researcher Lilianne Mujica-Parodi. But that aging effect happens faster.
"It's like losing 10 years," said Mujica-Parodi, a professor at Stony Brook University School of Medicine in New York.
The findings — published May 24 in the medical journal eLife — add to a body of research on diabetes and brain health. That includes many studies linking diabetes to a faster decline in mental sharpness during older age, and a higher risk of dementia.
In type 2 diabetes, the body cannot properly use the hormone insulin, which allows body cells to consume glucose (sugar) for energy. As a result, blood sugar levels are chronically high — which can damage blood vessels and nerves throughout the body. People with the disease are at risk of such serious complications as heart disease, kidney disease and stroke.
But the diabetes-brain connection goes beyond that, according to Mujica-Parodi. The brain is a "huge consumer" of glucose, she said, and if brain cells (neurons) cannot use insulin, they are in trouble.
"If you starve a neuron, it's going to atrophy," Mujica-Parodi said. She suspects it's this neuron starvation, rather than blood vessel damage, that is the main force driving the faster brain aging.
The findings are based on just over 20,000 adults, ages 50 to 80, who were part of an ongoing research project called the U.K. Biobank. They took standard tests of cognitive abilities such as memory, information processing speed, and executive function — skills, such as planning and organization, that we use to accomplish daily tasks.
A smaller group also underwent MRI brain scans.
On average, the study found, people with type 2 diabetes scored lower on the cognitive tests, compared to diabetes-free people of the same age, sex and education level. Their executive function scores were 13% lower, and their processing speed performance was nearly 7% lower.
On MRI, both groups showed age-related tissue thinning in the same brain areas — particularly a region called the ventral striatum, which is critical to executive function. But people with diabetes had a greater degree of atrophy.
The findings do suggest that people with diabetes are showing an "accelerated aging" in the brain, said Michal Beeri, a professor of psychiatry at Mount Sinai's Icahn School of Medicine in New York City.
Beeri, who was not involved in the research, studies the relationship between diabetes and mental performance. She said she thinks cerebrovascular disease — damage to the blood vessels supplying the brain — is the primary reason diabetes drains mental sharpness.
But it is possible, Beeri said, that multiple mechanisms, including neuron starvation, are at work.
Whatever the underlying reasons, both she and Mujica-Parodi stressed the connection between the brain and the rest of the body.
"We tend to think of the body and brain as two separate things," though that is clearly not the case, Mujica-Parodi said.
"There's no reason to think that your diabetes stops at your neck," Beeri agreed. "I'm surprised that when doctors talk to their patients with diabetes, they are often not bringing up brain health."
If diabetes contributes to cognitive decline, does treating diabetes help?
"In theory, good glucose control should reduce the risk," Beeri said.
Studies have linked use of diabetes medications, like metformin, to lesser risk of mental decline. But, Beeri said, those studies do not prove the medications, themselves, deserve the credit.
Clinical trials testing metformin and certain other diabetes drugs for brain benefits are underway.
In the current study, metformin use was not linked to any brain protection. But, Mujica-Parodi said, that finding is not conclusive.
Plus, Beeri said, good diabetes control is important for many reasons, and is "something people should be doing anyway."
Prevention, however, is ideal, Beeri pointed out. Some risk factors for type 2 diabetes -- like older age and family history — cannot be changed. But a healthy diet, exercise and losing excess weight can do much to prevent the disease, she said.