When we removed low-quality studies, significantly increased T2DM risk was found in overall analysis (model 1: OR = 2.57, 95% CI = 1.53–4.31, Table 5), and when we removed HWD, significantly association was revealed in the overall analysis (model 1: OR = 1.72, 95% CI = 1.15–2.58; model 3: OR = 1.30, 95% CI = 1.01–1.67; model 4: OR = 2.24, 95% CI = 1.41–3.54; model 5: OR = 1.42, 95% CI = 1.01–2.01; model 6: OR = 1.48, 95% CI = 1.03–2.15) combined effects on GSTM1 and GSTP1 polymorphisms. The gene discussed is GSTP1; the disease is type 2 diabetes mellitus.