Nonlinear Relationship Between Triglyceride‐to‐High‐Density Lipoprotein Cholesterol Ratio and Non‐Alcoholic Fatty Liver Disease: A Secondary Retrospective Analysis Based on a Japanese Longitudinal Study

Background The purpose of this research is to investigate the particular connection between the triglyceride to high‐density lipoprotein cholesterol ( TG / HDL ‐C) ratio and non‐alcoholic fatty liver disease ( NAFLD ) to offer a more precise foundation for evaluating NAFLD risk. Methods This study involves a secondary analysis of a retrospective cohort study conducted from 2004 to 2015 in a Japanese population, which included 14,106 participants. The TG / HDL ‐C ratio was determined by the levels of triglycerides ( TG ) and high‐density lipoprotein cholesterol ( HDL ‐C). Participants were grouped according to the quartiles of TG / HDL ‐C. We analyzed the relationship between TG / HDL ‐C and NAFLD using Cox proportional hazards regression, smooth curve fitting, and sensitivity analysis. Results The average age of the study participants was 43.51 ± 8.89 years, with 7275 (51.57%) being male. After considering potential confounding factors, the study found a positive correlation between TG / HDL ‐C and NAFLD ( OR : 1.37, 95% CI : 1.31–1.43, p < 0.001). Moreover, a nonlinear relationship between TG / HDL ‐C and NAFLD was found, with a turning point at 1.42. The odds ratio ( OR ) on either side of this inflection point were 3.71 (95% CI : 2.87–4.79) on the left and 1.23 (95% CI : 1.17–1.29) on the right, indicating a stronger correlation when TG / HDL ‐C is below 1.42, particularly in younger individuals, females, and those with a BMI under 25 kg/m 2 . Conclusion The TG / HDL ‐C index shows a nonlinear positive correlation with NAFLD risk, particularly when the TG / HDL ‐C ratio is below 1.42, with a stronger association observed in younger individuals, females, and lower‐BMI populations.