Insulin Resistance Increases Alzheimer’s Risk

New research has found a connection between insulin resistance and the decline of memory function, which in turn increases the risk for Alzheimer’s disease.

Study authors evaluated the brain scans of 150 late middle-aged adults who were identified as being at risk for Alzheimer’s disease but displayed no signs of memory loss. The scans detected whether those with higher levels of insulin resistance—common in individuals who are obese, pre-diabetic or have type 2 diabetes—used less blood sugar in areas of the brain most susceptible to Alzheimer’s disease. When this occurs, the brain has less energy to function and relay information, according to the authors.
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“We suspect that there are optimal levels of glucose and insulin required for healthy brain function,” says Barbara B. Bendlin, PhD, an associate professor in the School of Medicine and Public Health at the University of Wisconsin, and co-author of the study.

Lifestyle interventions may help normalize glucose and insulin levels for patients in the process of developing insulin resistance—which results in abnormal blood glucose and insulin levels, says Bendlin.

“Both the Mediterranean and DASH diets have been associated with slower cognitive decline, possibly by reducing insulin resistance,” she says. “Exercise, including even light physical activity, can improve glucose and insulin levels, and exercise has been shown to have protective effects on the aging brain.”

With regard to patients with type 2 diabetes, managing blood glucose levels is likely important for maintaining brain health, she says, adding that “it’s important to keep in mind that, even though diabetes increases risk for developing Alzheimer's disease, there are several other factors involved in the development of Alzheimer's.”

As such, “not everyone with diabetes or associated metabolic disorders will develop cognitive decline. It's also of great interest to know if medications used to treat diabetes may be effective in preventing or delaying the onset of Alzheimer's disease,” she says, noting that trials are ongoing to determine if that is the case.

Moderate exercise—such as brisk walking, yard work, or yoga, for 30 total minutes on a given day, at least 3 times weekly—is the most important intervention to consider, adds Auriel A. Willette, MS, PhD, a professor of food science and human nutrition at Iowa State University, and lead author of the study.

Willette also recommends fewer calorie-heavy drinks, avoiding diet soft drinks, eating 1 light meal and usually moderating portions for other meals in a given day, noting that intermittent calorie restriction in clinical trials has been shown to reduce weight by 6% to 8% over an 8-week period, and reduce insulin resistance among patients who strongly desire to lose weight.

Aggressive management is required for patients with type 2 diabetes, he says.

“Beyond diet and exercise recommendations, controlling the disease with metformin, other drugs, and, if necessary, insulin may be best at reducing Alzheimer's disease risk. Clinical trials using intranasal insulin, which provide insulin directly to the brain, seem to maintain glucose metabolism in the brain, and also maintains memory function,” says Willette, adding that further studies are needed “to see if normal methods of controlling type 2 diabetes, or intranasal insulin or other new therapies, will reduce or eliminate risk for Alzheimer's disease.”

—Mark McGraw

Reference

Willette A, Bendlin, et al. Association of Insulin Resistance With Cerebral Glucose Uptake in Late Middle–Aged Adults at Risk for Alzheimer Disease. JAMA Neurol. 2015.