BDNF and type 2 diabetes mellitus: Multivariable logistic regression analysis was performed to investigate the risk factors of MCI in T2DM patients, including education levels (years), diabetes duration (years), the presence of CVD, serum HbA1c, HDL-C, creatinine, BDNF and apelin (OR = 0.304, 95%CI = 0.104–0.886; P = 0.029) (Table 3).