Researchers found that insulin and the cells that process it in the brain drop sharply in the early stages of Alzheimer's disease. They also found that insulin levels continue to decline as the disease progresses and becomes more severe.
"Insulin disappears early and dramatically in Alzheimer's disease. 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," says researcher Suzanne M. de la Monte, professor of pathology at Brown Medical School, in a news release.
Alzheimer's Disease Linked to Diabetes
In the study, researchers examined insulin and insulin receptor function in an area of the brain affected by Alzheimer's disease in brain tissue samples from people who died at various stages of the disease. They compared them to those with normal aging.
The results, published in the Journal of Alzheimer's Disease, showed that insulin levels decreased as the disease progressed.
In addition, researchers found levels of insulin receptors in the brain decreased with increasing severity of the disease. Low levels of insulin receptors impair the brain's ability to respond to insulin.
At the most advanced stage of Alzheimer's, the study showed insulin receptors were 80% lower than in a normal brain.
Researchers say insulin also plays a role in the production of the brain enzyme acetylcholine. Acetylcholine deficiency is associated with dementia and Alzheimer's disease.
"This has important implications for treatment," says de la Monte. "If you could target the disease early, you could prevent the further loss of neurons. But you would have to target not just the loss of insulin but the resistance of its receptors in the brain."