Serum vitamin D and lean non-alcoholic fatty liver disease: a nonlinear 'L-shaped' association in a national cross-sectional study.

This large-scale study is the first to identify a significant 'L-shaped' nonlinear association between serum vitamin D and lean NAFLD, wherein the association is most potent at concentrations below approximately 60 nmol/L. This finding highlights an epidemiological inflection point and underscores the need for nonlinear approaches in future research.