Heritability of Triglyceride-Glucose Index in Middle-Aged and Older Chinese Twins: Overall Estimates and Sex-Stratified Analysis

The triglyceride-glucose (TyG) index is a reliable composite marker of insulin resistance, which holds important clinical significance. Existing studies have predominantly focused on identifying TyG index-related genetic loci and single-nucleotide polymorphism (SNP)-based polygenic risk scores, however, the overall contribution of genetic factors to TyG index variation at the population level is still unclear. To address this gap, we conducted a classic twin study using data from the Qingdao Twin Registry in China. The study included 381 middle-aged and older Chinese twin pairs (241 monozygotic and 140 dizygotic), comprising 370 males and 392 females. The median age of participants was 50 (interquartile range: 12) years. Structural equation modeling was applied to estimate the heritability of the TyG index after adjusting for age, gender, and body mass index (BMI). Model fitting identified the AE model as the best-fitting one. Additive genetic effects (A) accounted for 60.48% (95% CI [52.46, 67.24]) of the total variance, while unique environmental effects (E) explained 39.52% (95% CI [32.76, 47.54]). A sex-limitation model was subsequently used to test for sex differences in TyG. The results showed that heritability was higher in females (67.2%) than in males (54.0%). This twin-based study provides robust evidence for a moderate‑to‑high heritability of the TyG index in a Northern Chinese population, underscoring the substantial genetic contribution to this composite insulin resistance marker. Notably, the sex difference in heritability reflects larger unique environmental variance in males, highlighting the differential contribution of environmental factors across sexes.