The role of body mass index in the association between serum vitamin D and non-alcoholic fatty liver disease: A mediation analysis

• There is an association between serum VD and NAFLD. • Sufficient VD was protective factor for NAFLD. • BMI partly mediated the association between serum VD and NAFLD. Non-alcoholic fatty liver disease (NAFLD) is a classic disease of liver injury, and studies have confirmed that nutrients can influence NAFLD. Findings on serum vitamin D (VD) and NAFLD are conflicting and the mechanisms are not yet clear. This study aimed to determine the association between the two and the mediating role mediated by body mass index (BMI). A cross-sectional study (N = 2609) was conducted using the 2017–2018 National Health and Nutrition Examination Survey (NHANES) dataset. Weighted multivariate logistic regression models estimated OR and 95 % CIs between serum VD and NAFLD. The mediation analysis was performed for BMI. Serum VD was statistically significant in subjects with and without NAFLD ( P = 0.026). Adequate serum VD was found to be a protective factor for NAFLD after adjusting for covariates (OR (95 %CI) of 0.717 (0.553,0.929)). After mediation analysis, it was found that BMI mediated 34.07 % of the effect of serum VD on NAFLD. There is an association between serum vitamin D and NAFLD and sufficient VD was protective factor for NAFLD. BMI partly mediated the association between serum VD and NAFLD.