Aging: Type 3 Diabetes

Diabetes and Alzheimer's disease may be related, but not in the way many researchers have suspected.

Scientists have long believed insulin was produced exclusively by the pancreas. Brown University scientists said they have surprising evidence that the brain makes its own insulin, the hormone that shuttles energy into the body's cells. They believe Alzheimer's disease may be triggered by what they have named "type 3" diabetes, a condition caused by the brain's inability to produce insulin. Diabetes has long been identified as a risk factor for Alzheimer's disease, but the mechanism has remained a mystery.

Examining postmortem human brain tissue, the researchers determined that a drop in the brain's insulin production contributes to the degeneration of brain cells, an early symptom of Alzheimer's. "If you destroy the ability of neurons to respond to insulin or if you take insulin away, neurons don't survive," says Suzanne de la Monte, a neuropathologist at Brown Medical School and an author of the study. The condition was found in the hippocampus, a region of the brain responsible for learning and memory.

So-called type 3 diabetes is confined to the brain and doesn't put other parts of the body at risk, says de la Monte. Other forms of the disease contribute to the risk for heart disease and stroke. The study appeared in the Journal of Alzheimer's Disease.