TNF and chronic obstructive pulmonary disease: From 7 relevant case–control studies, the following results were obtained: (1) visfatin level in COPD patients compared to healthy subjects did not show any significant difference based on meta-analysis, (2) correlation meta-analysis results indicated that there was a significant positive correlation between visfatin levels and IL-6 and TNF-α, and (3) results of the meta-regression analysis indicated that there was a direct correlation between pooled SMD visfatin and pooled SMD in age, BMI, FEV1, and IL-6 levels.