"Insulin disappears early and dramatically in Alzheimer's disease," senior researcher Suzanne M. de la Monte, a neuropathologist at Rhode Island Hospital and a professor of pathology at Brown University Medical School, said in a prepared statement.

"And many of the unexplained features of Alzheimer's, such as cell death and tangles in the brain, appear to be linked to abnormalities in insulin signaling. This demonstrates that the disease is most likely a neuroendocrine disorder, or another type of diabetes," she added.

The discovery that the brain produces insulin at all is a recent one, and de la Monte's group also found that brain insulin produced by patients with Alzheimer's disease tends to fall below normal levels.

Now her group has discovered that brain levels of insulin and its related cellular receptors fall precipitously during the early stages of Alzheimer's. Insulin levels continue to drop progressively as the disease becomes more severe -- adding to evidence that Alzheimer's might be a new form of diabetes, she said.

In addition, the Brown University team found that low levels of acetylcholine -- a hallmark of Alzheimer's -- are directly linked to this loss of insulin and insulin-like growth factor function in the brain.