RBP4 and type 2 diabetes mellitus: Although many studies have demonstrated that insulin resistance is one of the causes of diabetes, several population-based studies have shown that a positive correlation between RBP4 levels and the risk of T2DM still exists even when the insulin resistance indicator (HOMA-IR) is adjusted [55, 80], which indicates that RBP4 may increase the risk of diabetes through a pathway that does not completely overlap with insulin resistance.