The Association between Dietary Polyphenol and Non-Alcoholic Fatty Liver Disease Risk in Adults: A Systematic Review and Meta-Analysis of Observational Studies

Background: Non-alcoholic fatty liver disease (NAFLD) is regarded as a global health issue with increasing prevalence worldwide. Polyphenols play a pivotal role in alleviating inflammatory and oxidative stress pathways associated with the pathogenesis of NAFLD, however the literature are still scarce. Methods: This systematic review and meta-analysis was designed to investigate the association between dietary polyphenols and the risk of NAFLD with a meta-analysis approach. All observational studies in the online databases of PubMed, Scopus, Web of Science, Embase and Google Scholar up to June 2021 were searched, determining appropriate keywords, to identify relevant articles. Data were summarized using risk ratios (RRs) with 95% confidence intervals (CIs). Results: Of the total number of 4144 articles identified in the first phase of the literature search, 6 studies covering 21 arms on polyphenol intake and NAFLD risk containing 9436 participants in the case groups and 19996 participants in the control groups were included in study. The summary effect size (ES) for the risk of NAFLD, comparing the highest with lowest intakes of polyphenol, was 0.80 (95% CI: 0.77-0.83, P<0.0001, I2 = 0.0%;), indicating a significant inverse association. Conclusions: Our results proved that higher dietary intake of polyphenols can reduce the risk of NAFLD. However, due to small number of determined studies, these findings require further investigations to confirm recommendations for intensifying polyphenol intake in the general population.