Relationship between triglyceride-high-density lipoprotein cholesterol-glucose-body index and nonalcoholic fatty liver disease in Chinese middle-aged and older adults: a secondary analysis of a cross-sectional cohort

Nonalcoholic fatty liver disease (NAFLD) is a major public health issue in China’s aging population. Insulin resistance (IR) and metabolic dysregulation are key pathogenic factors, yet gold-standard assessment methods are complex and invasive, limiting clinical utility. The triglyceride-high-density lipoprotein cholesterol-glucose-body index (TyHGB index), derived from routine measures including triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), fasting plasma glucose (FPG), and body mass index (BMI), integrates core metabolic disturbances associated with NAFLD. Therefore, the primary aims of this study were to quantify the association between the TyHGB index and prevalent NAFLD, and to characterize its non-linear dose-response pattern and inflection point in middle-aged and older Chinese adults. This cross-sectional study included 1,592 Chinese adults aged 40 – 79 years. NAFLD was diagnosed by abdominal ultrasonography. The TyHGB index was analyzed as both a continuous variable and in quartiles. Multivariable logistic regression models were employed to assess its association with NAFLD, adjusting for a comprehensive set of covariates covering demographics, lifestyle, comorbidities, and metabolic parameters. Restricted cubic spline (RCS) models evaluated the dose-response relationship, with piecewise regression identifying potential inflection points. Subgroup analyses and receiver operating characteristic (ROC) curve analysis were conducted to test the robustness and discriminatory ability of the index for prevalent NAFLD. The prevalence of NAFLD was 61.12%. A significant positive association was found between the TyHGB index and NAFLD prevalence. In the fully adjusted model, each 1-unit increase in the TyHGB index was associated with an 18% higher odds of NAFLD (OR = 1.18, 95% CI: 1.10 – 1.27). Participants in Q4 had a 4.65-fold higher odds of NAFLD compared to those in Q1 (OR = 4.65, 95% CI: 3.04 – 7.13). RCS analysis revealed a significant non-linear dose-response relationship, with an inflection point at a TyHGB index of 9.33. Below this threshold, each 1-unit increase was associated with an 80.9% higher odds of NAFLD (OR = 1.81, 95% CI: 1.53 – 2.14), while no significant association was observed above the threshold. This positive association remained directionally consistent across all pre-specified subgroups, including age, gender, BMI, and metabolic status. Furthermore, the TyHGB index showed acceptable discriminatory ability for prevalent NAFLD, with an area under the curve (AUC) of 0.75 (95% CI: 0.73 – 0.78). Its AUC was higher than those of TG, HDL-C, or FPG alone, but performed only modestly better than BMI. At the optimal cutoff of 7.058, determined by maximizing the Youden index, the accuracy, sensitivity, and specificity were 0.72, 0.59, and 0.81, respectively, indicating a trade-off between relatively high specificity and modest sensitivity. In middle-aged and older Chinese adults, a higher TyHGB index is independently associated with an increased prevalence of NAFLD, exhibiting a clear non-linear dose-response relationship. This association remains robust across the majority of demographic and metabolic subgroups. Outperforming its individual lipid and glycemic components, the TyHGB index provides acceptable discriminatory ability comparable to BMI, making it a viable complementary screening and clinical stratification tool in health-check settings. Future prospective studies are required to establish causality and evaluate its longitudinal utility for NAFLD. Not applicable.