In a cohort study, Liang et al. reported that after 6 years in 2091, elderly patients in the highest RBP4 subgroup also had an increased risk of T2DM compared to those in the lowest quartile of RBP4 [51]; moreover, the risk of T2DM increased with increasing RBP4 concentration when RBP4 levels were higher than 50 μg/ml. Here, RBP4 is linked to type 2 diabetes mellitus.