INS and Alzheimer disease: Recently, growing evidence supports the concept that AD is a metabolic disease of type 3 diabetes mellitus, based on the fact that insulin resistance and dysfunctional glucose metabolism in the brain are often found in patients with AD and that Aβ deposition induces reduced expression of insulin receptor on neuronal cells (Zhao et al., 2008; de la Monte and Tong, 2014; Butterfield and Halliwell, 2019; Kellar and Craft, 2020).