In fact, our previous study reported a U-shaped relationship between serum RBP4 levels and the risk of incident T2DM, and the RBP4-diabetes association was independent of insulin resistance, which indicates that RBP4 may increase the risk of T2DM through pathway(s) that do not largely overlap with insulin resistance and that RBP4 might be involved in the pathogenesis of β-cell dysfunction, which could be involved in the association between higher RBP4 levels and T2DM [55]. Here, RBP4 is linked to diabetes mellitus.