NAMPT and type 2 diabetes mellitus: However, since it has been demonstrated that visfatin levels are increased both in T2D patients [94,95,96] and by hyperglycemia or insulin resistance induced by FFA infusion, whereas they are reduced by hyperinsulinemia [97,98], the increase in visfatin levels under diabetic condition may be the result of insulin deficiency (as occurs in long-lasting β-cell dysfunction) or its inability to suppress visfatin production in insulin-resistant conditions [97,99].