INS and type 2 diabetes mellitus: Considering the shared molecular and cellular features between type 1 diabetes, type 2 diabetes mellitus (T2DM), and insulin resistance in older adults, which are associated with memory impairment and cognitive decline, researchers have coined the term “Type 3 Diabetes mellitus (T3DM)” to emphasize the critical role of insulin in brain energy supply (Steen et al. 2005).