I just heard this theory this week and it seem to have a large amount of research which is tending to prove a link.
newsnetwork.mayoclinic.org
www.ncbi.nlm.nih.gov
We conclude that the term “type 3 diabetes” accurately reflects the fact that AD represents a form of diabetes that selectively involves the brain and has molecular and biochemical features that overlap with both type 1 diabetes mellitus and T2DM.
Mayo Clinic Minute: Is Alzheimer's Type 3 diabetes? - Mayo Clinic News Network
Are some cases of Alzheimer's disease triggered by a form of diabetes in the brain? Perhaps they are, according to researchers. Mayo Clinic's campuses in Rochester, Minnesota, and Jacksonville, Florida, recently participated in a multi-institution clinical study, testing whether a new insulin...
Dr. Bu has found genetics may also be to blame. A variant of the so-called Alzheimer’s gene, APOE4, seems to interfere with brain cells' ability to use insulin, which may eventually cause the cells to starve and die. Unofficially, it's called Type 3 diabetes. "What it refers [to] is that their brain's insulin utilization or signaling is not functioning. Their risk of developing Alzheimer’s disease is about 10 to 15 times higher."
Alzheimer's Disease Is Type 3 Diabetes–Evidence Reviewed - PMC
Alzheimer's disease (AD) has characteristic histopathological, molecular, and biochemical abnormalities, including cell loss; abundant neurofibrillary tangles; dystrophic neurites; amyloid precursor protein, amyloid-β (APP-Aβ) deposits; increased ...