Insulin and Alzheimer

Study Links Insulin with Alzheimer's

09-AUG-2005

Elevated levels of insulin in the body can go straight to the brain, causing inflammation and increasing levels of a protein seen in abundance in patients with Alzheimer's disease, according to a new study from researchers at the Veterans Affairs Puget Sound Healthcare System and the University of Washington.

Insulin is a hormone that helps regulate blood sugar. Obesity, high blood pressure and diabetes are associated with a condition called insulin resistance, in which the body needs more and more insulin to balance sugar levels. The reaction is akin to building up a resistance to a drug.

That flood of insulin has long been linked to damaging inflammation in other areas of the body, but this is the first study to demonstrate an effect in the brain.

According to some estimates, about 40 percent of Americans over 60 years old have insulin resistance, said Suzanne Craft, author of the study, a professor of psychiatry at the University of Washington and a researcher at the VA

"This is not just a few patients," she said.

The study was posted online Monday and will be published in the October issue of the Archives of Neurology.

"Improving insulin resistance and lowering blood insulin levels may reduce inflammation and reduce the risk of Alzheimer's," Craft said.

The two-day study included 16 healthy adults between the ages of 55 and 81.

On the first day, they received a high dose of insulin, followed by a saline injection on the second day.

Researchers examined their spinal fluid drawn each day for B-amyloid, a protein that accumulates in the brains of Alzheimer's patients, and markers for inflammation.

On insulin day, the participants received enough of the hormone to mimic the effect of eating a high-fat, high carbohydrate diet for someone with insulin resistance.

The effect was dramatic, even in otherwise healthy people.

"What we saw was this very striking increase in the inflammation markers with the insulin infusion," compared with the day of the saline injections, Craft said.

Craft estimates between 40 percent and 50 percent of Alzheimer's disease is related to long-term exposure to unhealthy insulin levels.

Dr. Natalie Rasgon, an associate professor of psychiatry at Stanford University, said the study significantly adds to what's already known about the dangers of too much insulin circulating in the body.

"She (Craft) took normal healthy people, with nothing alerting us to potential neurodegenerative disease and she created a metabolic state in them, which is well-known as a major risk factor of a number of illnesses -- not just Alzheimer's," Rasgon said.

Still, the study doesn't suggest that every person with diabetes or other insulin resistant conditions is headed toward Alzheimer's, Rasgon said.

"It doesn't mean that everyone will go on to develop that disease," Rasgon said. "But those who have other risk factors (should) be more vigilant about their diets."

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