Figure 5 illustrates the efficacy of DPP4 inhibitors on HBA1c. A fixed-effect model was used in 434 subjects in the experimental group and 441 in the control group. After standardization, compared with the control group, the HBA1c of the experimental group decreased by 0.34 (95% CI [−0.48, −0.21]), and the I2 value was 89% (P < 0.05), indicating that DPP4 inhibitor can effectively reduce HBA1c, so as to improve the cognitive impairment of diabetic patients. This evidence concerns the gene DPP4 and Cognitive impairment.