XDH and type 2 diabetes mellitus: In this study, insulin resistance index (28) (indicated by HOMA-IR), serum lipids (including TCHO, TG, HDL-C, and LDL-C) (29), and serum XO activity (30) were included in the mediation analysis because all of them might be potential mediators that play vital roles in the pathogenesis and development of type 2 diabetes.