The effect of longitudinal trajectories of triglyceride-glucose index on the new-onset non-alcoholic fatty liver disease

Background The triglyceride-glucose (TyG) index is a reliable marker of insulin resistance and has been linked to various metabolic disorders. Non-alcoholic fatty liver disease (NAFLD) is a prevalent metabolic liver disease,especially among the elderly. The relationship between changes in the TyG index and NAFLD onset is not fully understood. Our study examines the association between changes in the TyG index and the onset of NAFLD among elderly participants. Method We conducted a prospective cohort study involving 28,535 elderly participants, selected based on their participation in annual health checkups from 2018 to 2021 and having complete triglyceride and fasting blood glucose values, which met our inclusion criteria. The group-based trajectory model was used to identify three distinct TyG trajectory groups: the low-stable group, moderate-stable group, and high-stable group. The incidence of NAFLD in each group was followed up at the 2022 and 2023 checkups. We calculated the differences in cumulative incidence of TyG across the groups and utilized Cox proportional hazard models to estimate risk ratios and 95% confidence intervals for NAFLD onset among the groups. To further minimize the influence of other risk factors on the results, those with BMI > 28 and those taking medications were excluded, respectively, and the models were adjusted for sensitivity analysis. Restricted cubic spline regression was applied to evaluate the baseline dose-response relationship between the TyG index and NAFLD. Results The study included a total of 28,535 participants, comprising 13,456 males (47.16%) and 15,079 females (52.84%). The cumulative incidence rates of NAFLD were 7.10% in the low-stable group, 16.10% in the moderate-stable group, and 23.20% in the high-stable group, increasing significantly with rising TyG trajectories ( P  < 0.001). Cox proportional hazards modeling after adjusting for confounders such as age, sex, blood pressure, BMI, blood glucose, and lipids showed that the risk of NAFLD in the moderate-stable group and the high-stable group was 1.682 (95% CI: 1.541–1.835) and 2.279 (95% CI: 1.998–2.599) times higher than that of the low-stable group ( P  < 0.001).NAFLD risk progressively increased with higher TyG levels, with critical cut-off values set at 8.56 for the total population. Conclusion People with consistently high TyG levels have a higher risk of developing NAFLD, and this risk increases progressively as TyG levels rise.