Plasma retinol and RBP4 levels strongly correlated in all subjects combined (r = 0.881, p < 0.001), as well as in T2DM subjects (r = 0.900, p < 0.001) and non-diabetic subjects separately (r = 0.859, p < 0.001) (Figure 2). Here, RBP4 is linked to type 2 diabetes mellitus.