INS and type 2 diabetes mellitus: Type 2 diabetes mellitus (T2DM) is a heterogeneous metabolic disorder characterized by reduced insulin sensitivity and relative insulin deficiency, which increases the risk for cognitive decline and dementia, such as Alzheimer’s disease (AD) and vascular dementia (Biessels et al., 2006; Kopf and Frolich, 2009; McCrimmon et al., 2012).