Diabetes, Alzheimer's Link Further Defined

Having insulin resistance or type 2 diabetes raises the risk of developing brain plaques associated with Alzheimer's disease, says new research in the medical journal Neurology.

Researchers found that people with the highest levels of fasting insulin had nearly six times the odds of having plaque deposits between nerves in the brain, compared to people with the lowest levels of fasting insulin.

Based on study findings, those with the highest scores on a measure of insulin resistance had about five times the odds of having brain plaques vs. those with the lowest scores on the insulin-resistance test.

Insulin resistance is a problem where cells become less able to use insulin effectively.

Plaque Development Aligns with Diabetes Factors

Study author Dr. Kensuke Sasaki, at Kyushu University in Fukuoka, Japan, says the risk of plaque-type Alzheimer's disease pathology increases in a linear relationship with diabetes-related factors.

According to the Alzheimer's Association (AA), plaques build up between nerve cells. They contain deposits of a protein fragment called beta-amyloid. Tangles are twisted fibers of another protein called tau. Tangles form inside dying cells.

Though most people develop some plaques and tangles as they age, states the AA, those with Alzheimer's tend to develop far more. The plaques and tangles tend to form in a predictable pattern, beginning in areas important in learning and memory and then spreading to other regions.

While numerous studies have found a link between cognitive decline and dementia in people with type 2 diabetes, the current study sought to determine the reason for that link.

In order to study brains, researchers use autopsies. Plaques and tangles are thought by many to be the two main causes of the destruction of brain tissue seen in Alzheimer's disease.

Looking at autopsies from 135 Japanese adults, the researchers were able to compare if different measures of insulin resistance or type 2 diabetes correlated with the development of plaque deposits as well as tangles.

As part of a study like this, researchers also look at age, sex, blood pressure, cholesterol, body-mass index, smoking, exercise, and cerebrovascular disease to understand the complete health picture.

Those studied in an autopsy had been tested a decade earlier while they were living. The tests included an oral 2-hour glucose tolerance test, fasting blood sugar, and insulin levels. In addition, researchers measured insulin resistance using a test called homeostasis assessment of insulin resistance (HOMA-IR).

The study found no link between diabetes risk factors and the development of tangles.

However, higher levels of blood sugar two hours after eating, high fasting insulin levels, and an elevated HOMA-IR score were associated with an increased risk of developing plaques.

Fasting blood sugar levels were not linked with an increased risk of plaques.

ApoE4 Gene also Implicated in Study

The researchers also looked to see if the presence of a gene long implicated in Alzheimer's disease, ApoE4, would have an effect on the association between diabetes risk factors and the development of plaques.

They found that individuals with the ApoE4 gene had the strongest association between high blood sugar levels, insulin resistance, and fasting insulin levels and the development of plaques.

Dr. William Thies, chief medical and scientific officer for the Alzheimer's Association, says, "This area is being pretty aggressively researched for a number of reasons."

He asks, "Would better control of type 2 diabetes improve the cognitive fate of those with the disease, and is there some way we can intervene in glucose metabolism that might affect Alzheimer's?

"Although we don't know anything that can prevent Alzheimer's disease right now, I do think there are a lot of good reasons for people to try to prevent type 2 diabetes, much of which can potentially be avoided with regular physical activity and weight maintenance," says Dr. Thies.

"Preventing or controlling diabetes is good for all kinds of reasons, and also because it might contribute to your risk of Alzheimer's disease," he says.

Always consult your physician or other healthcare provider for more information.