Comment on “Exposure to air pollution is associated with an increased risk of metabolic dysfunction-associated fatty liver disease”

We read with great interest the article by Guo et al. reporting the association of air pollution (AP) and metabolic dysfunction-associated fatty liver disease (MAFLD).(1Guo B. Guo Y. Nima Q. Feng Y. Wang Z. Lu R. et al.Exposure to air pollution is associated with an increased risk of metabolic dysfunction-associated fatty liver disease.J Hepatol. 2021; Abstract Full Text Full Text PDF Scopus (2) Google Scholar) We appreciate the authors conducted a great cohort study and provided a novel perspective. However, we would like to highlight some key points. Firstly, authors demonstrated that odds ratios (ORs) of MAFLD associated with AP, stratified by demographic and life style factors in table 2. However, we are worried that some important residual confounders might exist, especially the annual household income and education level because of the association with the prevalence of diabetes, which was one of the criteria of MAFLD.(2Eslam M. Newsome P.N. Sarin S.K. Anstee Q.M. Targher G. Romero-Gomez M. et al.A new definition for metabolic dysfunction-associated fatty liver disease: An international expert consensus statement.J Hepatol. 2020; 73: 202-209Abstract Full Text Full Text PDF PubMed Scopus (669) Google Scholar, 3Seiglie J.A. Marcus M.E. Ebert C. Prodromidis N. Geldsetzer P. Theilmann M. et al.Diabetes Prevalence and Its Relationship With Education, Wealth, and BMI in 29 Low- and Middle-Income Countries.Diabetes Care. 2020; 43: 767-775Crossref PubMed Scopus (30) Google Scholar, 4Worldwide trends in diabetes since 1980: a pooled analysis of 751 population-based studies with 4.4 million participants.Lancet. 2016; 387: 1513-1530Abstract Full Text Full Text PDF PubMed Scopus (1974) Google Scholar) Moreover, the income and education level could also affect the life styles and quality. Therefore, we suggest the authors may add another co-medication status in the stratified analyses to avoid residual confounders. Secondly, the authors indicated sex may influence the association between AP and MAFLD, and males had significantly higher MAFLD prevalence than females in overweight or obese adults.(5Liu J. Ayada I. Zhang X. Wang L. Li Y. Wen T. et al.Estimating Global Prevalence of Metabolic Dysfunction-Associated Fatty Liver Disease in Overweight or Obese Adults.Clin Gastroenterol Hepatol. 2021; Google Scholar) In other words, the gender was an independent factor of MAFLD. In addition, according to table 2, PM2.5 and PM10 seemed not to have significantly additive effect on MAFLD with central obesity, and there could be some contradiction. Hence, we suggest that authors propose more mechanisms about the results. Lastly, authors indicated that the OR of MAFLD associated with AP were greater in non-diabetic group, but not significantly different. We are concerned that there could be type I error, because air pollution could exacerbate the parameters of diabetes.(6Hwang M.J. Kim J.H. Koo Y.S. Yun H.Y. Cheong H.K. Impacts of ambient air pollution on glucose metabolism in Korean adults: a Korea National Health and Nutrition Examination Survey study.Environ Health. 2020; 19: 70Crossref PubMed Scopus (9) Google Scholar) Thus, we suggest authors should match or adjust co-medication status in the stratified analyses. The study result is interesting and provocative. Yet, we recommend that residual confounders should be considered and proposing more potential mechanisms would enrich the study credibility. The authors have no conflicts of interest that pertain to this work to declare. Conceptualization, Y.-S.C. and J.C.-C.W.; Supervision, Y.-M.H. and J.C.-C.W.; Writing—original draft, Y.-S.C.; Writing—review & editing, Y.-M.H. and J.C.-C.W. All authors have read and approved the final manuscript. This article received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Exposure to air pollution is associated with an increased risk of metabolic dysfunction-associated fatty liver diseaseJournal of HepatologyVol. 76Issue 3PreviewAccumulating animal studies have demonstrated the harmful contribution of ambient air pollution (AP) to metabolic dysfunction-associated fatty liver disease (MAFLD), but corresponding epidemiological evidence is limited. We examined the associations between long-term AP exposure and MAFLD prevalence in a Chinese population. Full-Text PDF Open Access