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

  • Author Footnotes
    † Yu-Syuan Chen and Yao-Min Hung contributed equally to this work as first authors.
    Yu-Syuan Chen
    Footnotes
    † Yu-Syuan Chen and Yao-Min Hung contributed equally to this work as first authors.
    Affiliations
    Student of Medicine, Chung Shan Medical University, Taichung, Taiwan
    Search for articles by this author
  • Author Footnotes
    † Yu-Syuan Chen and Yao-Min Hung contributed equally to this work as first authors.
    Yao-Min Hung
    Footnotes
    † Yu-Syuan Chen and Yao-Min Hung contributed equally to this work as first authors.
    Affiliations
    Department of Internal Medicine, Kaohsiung Municipal United Hospital, Kaohsiung, Taiwan
    Search for articles by this author
  • James Cheng-Chung Wei
    Correspondence
    Corresponding author. Addresses: Department of Allergy, Immunology & Rheumatology, Chung Shan Medical University Hospital, Taichung, Taiwan; Institute of Medicine, College of Medicine, Chung Shan Medical University; Graduate Institute of Integrated Medicine, China Medical University (J.C.-C. Wei).
    Affiliations
    Department of Allergy, Immunology & Rheumatology, Chung Shan Medical University Hospital, Taichung, Taiwan

    Institute of Medicine, College of Medicine, Chung Shan Medical University

    Graduate Institute of Integrated Medicine, China Medical University, Taichung, Taiwan
    Search for articles by this author
  • Author Footnotes
    † Yu-Syuan Chen and Yao-Min Hung contributed equally to this work as first authors.
Published:January 21, 2022DOI:https://doi.org/10.1016/j.jhep.2021.12.032

      Linked Article

      To the Editor:
      We read with great interest the article by Guo et al. reporting on the association of air pollution (AP) with metabolic dysfunction-associated fatty liver disease (MAFLD).
      • Guo 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.
      We appreciate the authors conducted a great cohort study and provided a novel perspective. However, we would like to highlight some key points.
      Firstly, the authors reported the odds ratios (ORs) of MAFLD associated with AP, stratified by demographic and lifestyle 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.
      • Eslam 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.
      • Seiglie 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.
      Worldwide trends in diabetes since 1980: a pooled analysis of 751 population-based studies with 4.4 million participants.
      Moreover, income and education levels could also affect lifestyle and quality of life. Therefore, we suggest the authors may add another co-medication status (e.g. income and education level) 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.
      • Liu 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.
      In other words, sex was an independent risk factor for MAFLD. In addition, according to Table 2, PM2.5 and PM10 seemed not to have a significantly additive effect with central obesity, which seems to be a contradiction. Hence, we suggest that the authors propose more mechanisms to explain their results.
      Lastly, the authors indicated that the OR of MAFLD associated with AP were greater in the non-diabetic group, but not significantly different. We are concerned that there could be type I error, because AP could exacerbate the parameters of diabetes.
      • Hwang 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.
      Thus, we suggest that the 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 more potential mechanisms proposed to further develop on the results of this study.

      Financial support

      This article received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

      Authors' contributions

      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.

      Conflict of interest

      The authors have no conflicts of interest that pertain to this work to declare.
      Please refer to the accompanying ICMJE disclosure forms for further details.

      Supplementary data

      The following are the supplementary data to this article:

      References

        • Guo 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. 2022; 76: 518-525
        • Eslam 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: 202-209
        • Seiglie 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: 767-775
      1. Worldwide trends in diabetes since 1980: a pooled analysis of 751 population-based studies with 4.4 million participants.
        Lancet. 2016; 387: 1513-1530
        • Liu 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;
        • Hwang 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: 70