An American research team found that memory-forming parts of the brain were protected by the hormone released by the pancreas to help control levels of sugar in the blood.
The study suggests that insulin may slow or prevent the memory loss caused by toxic proteins which attack the brains of Alzheimer's sufferers.
The research, carried out at the Northwestern University in Illinois, US, and the Federal University of Rio de Janeiro in Brazil, supports the idea that the disease could be a type of brain diabetes.
Researchers carried out the study by treating neurons taken from one of the brain's memory centres - the hippocampus - with insulin and the diabetes drug rosiglitazone.
Cells in the hippocampus are susceptible to damage caused by ADDLs (amyloid beta-derived diffusible ligands), toxic proteins that build up in people with Alzheimer's disease.
Researchers found that the insulin blocked exposure to ADDLs, preventing them from attaching to memory cells.
Senior author William Klein, a researcher in Northwestern's Cognitive Neurology and Alzheimer's Disease Centre, said: 'Sensitivity to insulin can decline with ageing, which presents a novel risk factor for Alzheimer's disease. Our results demonstrate that bolstering insulin signalling can protect neurons from harm.'
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