From Our 2007 Archives

Diabetes Linked to Alzheimer's Disease

Experts Fear Rise in Diabetes May Lead to Alzheimer's Epidemic

By Daniel J. DeNoon
WebMD Health News

Reviewed By Louise Chang, MD

June 26, 2007 (Chicago) -- New findings suggest that poorly controlled diabetes may lead to Alzheimer's disease.

The worry is that today's mushrooming diabetes epidemic will become tomorrow's Alzheimer's epidemic, researchers said at the American Diabetes Association's 67th Annual Scientific Sessions, held June 22-26 in Chicago.

Recent findings suggest that diabetes speeds -- and may even cause -- Alzheimer's disease, said neurologist Sudha Seshadri, MD, of Boston University.

"In both men and women, diabetes is associated with lower brain volume," Seshadri said. "The magnitude was quite substantial."

Indeed, the brains of people with diabetes are about "10 years older" than the brains of same-age people without diabetes, Seshadri said.

Like a detective linking a suspect to a crime, Seshadri pieced together the evidence linking diabetes to increased risk of Alzheimer's disease.

"Even if it were not a direct cause, diabetes may hasten the onset of clinical manifestations of Alzheimer's disease because the brain goes downhill faster," she said. "But diabetes and Alzheimer's may share underlying genetic and pathophysiologic pathways. Diabetes may directly impact Alzheimer's prevalence."

Insulin/Alzheimer's Link

The central problem in diabetes is the body's inability to regulate blood sugar through the hormone insulin.

But insulin does a lot more than regulate blood sugar, notes Suzanne Craft, PhD, professor of psychiatry and behavioral science at the University of Washington, Seattle, and a researcher at the VA Puget Sound Medical Center.

"Insulin plays a role in normal cognitive function -- and dysregulation of insulin increases risk for cognitive impairment, Alzheimer's disease, and other neurodegenerative diseases," Craft said at the American Diabetes Association meeting.

Insulin has a particularly strong effect on memory, Craft and colleagues have found. At the right doses, insulin actually improves memory. Indeed, Craft's team is conducting a clinical trial of a device that squirts insulin into the nose in a manner that takes it to the brain but not to the rest of the body.

Preliminary results from this so-called Study of Nasal Insulin to Fight Forgetfulness -- SNIFF -- show that insulin can boost both memory and attention to tasks in patients with early-stage Alzheimer's disease.

An opposite effect is seen in people with insulin resistance, Craft says, even before they develop type 2 diabetes.

"The increasing prevalence of insulin resistance is worrisome from a public health standpoint," she said. "Does this foreshadow an impending dementia epidemic?"

Craft has also found that the relatively high levels of insulin in people with type 2 diabetes may spur development of the amyloid protein that is present in the brains of Alzheimer's patients. High insulin levels may also trigger a cascade of potentially harmful chemical signals in the brain.

High levels of insulin "may create a neurobiological context for later degenerative brain diseases," Craft said.

She urged diabetes researchers to include measures of cognitive function in all future clinical trials of diabetes treatments.

SOURCES: American Diabetes Association 67th Annual Scientific Sessions, Chicago, June 22-26, 2007. Sudha Seshadri, MD, associate professor, Boston University. Suzanne Craft, PhD, professor of psychiatry and behavioral science, University of Washington, Seattle, and the VA Puget Sound Medical Center.

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