BACKGROUND AND AIM: To synthesize data on circulating tumor necrosis factor (TNF)-α levels between patients with histologically confirmed non-alcoholic fatty liver disease (NAFLD) (simple steatosis or non-alcoholic fatty liver [NAFL] and/or non-alcoholic steatohepatitis [NASH]) and controls.
METHODS: We performed a systematic search in PubMed, Scopus, and Cochrane Library. Fifty-six studies, published between 2003 and 2019, were finally included, reporting data from 5848 individuals (1634 controls and 4214 NAFLD patients).
RESULTS: Higher circulating TNF-α levels were observed in NAFLD patients than controls (standardized mean difference [SMD] 0.84; 95% confidence interval [95% CI] 0.59-1.09), NAFL patients than controls (SMD 0.56; 95% CI 0.27-0.85), NASH patients than controls (SMD 0.93; 95% CI 0.64-1.22), and NASH than NAFL patients (SMD 0.31; 95% CI 0.16-0.46). There were only minimal changes in the comparisons between groups after excluding studies with morbidly obese populations (n = 11), or pediatric/adolescent populations (n = 6), or other than enzyme-linked immunosorbent assay method of TNF-α measurement (n = 8). There was high heterogeneity among studies in all comparisons, which was not essentially affected after sensitivity analyses. The meta-regression analysis revealed that the male ratio was positively associated with TNF-α SMD in the comparison between patients with NASH and NAFL (beta = 0.809; 95% CI 0.052-1.566) and accounted for 36% (P = 0.037) of the heterogeneity in this pair of comparison. TNF-α SMD was not associated with age, body mass index, and alanine aminotransferase in any pair of comparisons.
CONCLUSIONS: Circulating TNF-α levels were higher in patients with NAFLD compared with controls. Higher levels of circulating TNF-α were also associated with the severity of NAFLD.