The triglyceride-glucose index is an indicator of sarcopenia

Characteristics of the participants

A total of 10,537 people were included with an average age of 59.34 ± 10.09 years, a total proportion of 54% women and 73.9% people living in the village. Compared to individuals with sarcopenia, those without sarcopenia showed higher TG, FBG, BMI, WC, and grip strength ASM/Ht²and TyG-related index and SI, and fewer had hypertension, hyperlipidemia, hyperglycemia, and cardiac disease (Table 1).

Predictive value of SI in incident sarcopenia

The SI differed between the sarcopenia and severe sarcopenia groups in patients without sarcopenia; it also differed significantly between the possible sarcopenia and sarcopenia and severe sarcopenia groups (Fig. 1A). SI was associated with sarcopenia (OR 0.988).[0.982,0.995], P= 4.03E-4) and there were differences between groups in the presence or absence of hyperglycemia, hypertension, hyperlipidemia, and cardiac disease (Table 2). Sensitivity analysis showed that differences between groups remained significant; However, the association between SI and sarcopenia was not significant after accounting for antidiabetic medications, lipid-lowering medications, and healthy physical activity (Supplementary Table 1). There was an association between SI and physical performance and a nonsignificant association with muscle strength and muscle mass (Supplementary Table 2). For the SI, the AUC was 0.609, with a cutoff value of 0.905, a sensitivity of 58.90%, and a specificity of 57.90% (Fig. 3A). No difference was found between the two groups in the cumulative incidence of sarcopenia according to the cutoff value subgroups (Supplementary Figure 3) and the Cox risk model results showed an HR of 0.812 (0.473, 1.394) for SI and sarcopenia (Table 3). The nonlinear association between SI and sarcopenia was also not significant (P= 0.625) (Fig. 4A).

Difference in TyG-related index between sarcopenia categories

To better understand the differences between sarcopenia and the TyG-related index, we divided participants into four groups: no sarcopenia, possible sarcopenia, sarcopenia and severe sarcopenia. The TyG-related index differed significantly between the four groups. The TyG-related index differed between the sarcopenia group and the severe sarcopenia group in patients without sarcopenia; It also differed significantly between the possible sarcopenia and sarcopenia and severe sarcopenia groups, but not significantly between the no sarcopenia and possible sarcopenia groups in patients. Furthermore, there were no significant differences between the sarcopenia and severe sarcopenia groups (Fig. 1B-D). We also observed that the mean values ​​of the TyG-related index were lower in the sarcopenia and severe sarcopenia groups than in the no sarcopenia and possible sarcopenia groups.

Associations of TyG-related index with sarcopenia

The TyG-related index was associated with sarcopenia, with an odds ratio (OR) of 0.961 (0.955, 0.968); 0.872 (0.867,0.878); and 0.896 (0.890, 0.902) for TyG index, TyG BMI index and TyG WC index, respectively (Table 2). The TyG-related index was also significantly associated with muscle strength (OR_{TyG index} 0.979[0.971,0.987], P= 1.31E-7; OR_{TyG BMI index} 0.974[0.966,0.982], P= 1.43E-10; OR_{TyG-wc index} 0.978[0.970,0.986], P= 4.78E-8) and muscle mass (OR_{TyG index} 0.954[0.947,0.962], P= 2.00E-16; OR_{TyG BMI index} 0.829[0.823,0.834], P= 2.00E-16; OR_{TyG-wc index} 0.963[0.857,0.869], P= 2.00E-16), but not with physical performance (Supplementary Table 2). We found positive correlations between the TyG-related index and the magnitude of grip strength (β)._{TyG index} = 0.053, P= 2.90E-12; β_{TyG BMI index} = 0.099, P= 2.00E-16; β_{TyG-wc index} = 0.096, P= 2.00E-16) and ASM/Ht² (β_{TyG index}= 0.114, P= 2.00E-16; β_{TyG BMI index}= 0.643, P= 2.00E-16; β_{TyG-wc index}= 0.385, P= 2.00E-16), but negative correlations with SI (β_{TyG index}= -0.089, P= 2.00E-16; β_{TyG BMI index}= -0.046, P= 2.00E-16; β_{TyG-wc index}= -0.038, P= 3.00E-14) (Fig. 2), and only TyG-WC was positively associated with the reaction time in the 5-time chair stand test (β = 0.038, P= 3.00E-4) (Supplementary Table 3).

Associations between TyG-related index and handgrip strengthening, ASM/Ht² and sarcopenia index. Abbreviations: ASM/Ht2, appendicular skeletal muscle mass divided by the square of height; TyG, triglyceride glucose index; BMI, body mass index; WC, waist circumference. All factors adjusted for age, gender, place of residence, education, hyperlipidemia, hypertension, hyperglycemia, heart disease, stroke, systolic, diastolic, high density lipoprotein and low density lipoprotein.

We analyzed subgroups by age, sex, and presence of hypertension, hyperlipidemia, hyperglycemia, cardiovascular disease, and stroke. In all subgroups, there was an association between the TyG-related index and sarcopenia, showing a trend consistent with that of the overall population (Table 2). The results remained robust after sensitivity analysis (Supplementary Table 1).

Predictive potential of the TyG-related index for incident sarcopenia

We used ROC curves to investigate whether the TyG-related index can predict sarcopenia. For the TyG index, the AUC was 0.659, with a cutoff value of 8.564, a sensitivity of 69.40% and a specificity of 54.80%. For the TyG BMI index, the AUC was 0.903, with a cutoff value of 182.558, a sensitivity of 83.80% and a specificity of 81.70%. For the TyG-WC index, the AUC was 0.819, with a cutoff value of 700.899, a sensitivity of 80.50%, and a specificity of 69.90% (Fig. 3B-D). In addition, five-fold cross-validation showed that the TyG BMI index had the highest AUC among the four indices, with an AUC of 0.826, a sensitivity of 95.20% and a specificity of 69.90% (Supplementary Table 4). Our subgroup analyzes revealed that the TyG-related index had a larger area under the AUC curve than the total area in men, the elderly, and those with hyperglycemia, hyperlipidemia, hypertension, and heart disease (Supplementary Table 5). In particular, the TyG BMI showed a good predictive effect both overall and in various subgroups.

ROC curves associated with TyG-related index and sarcopenia index for sarcopenia. (A) ROC curves of sarcopenia index. (B) ROC curves of TyG index. (C) ROC curves of TyG BMI index. (D) ROC curves of the TyG-WC index. Abbreviations: HR, hazard ratio; CI, confidence interval; TyG, triglyceride glucose index; BMI, body mass index; WC, waist circumference

TyG-related index and sarcopenia incident risk

We divided the TyG-related index into two groups based on cutoff values, and survival analyzes showed significant differences in incidence between the two groups at the 4-year follow-up time point (Supplementary Figure 2). The Cox proportional hazard model showed that the risk of sarcopenia was reduced by 37.3% (HR 0.623).[ 0.502,0.774]), 4.8% (HR 0.952[0.947,0.958]), 0.4% (HR 0.996[0.995,0.996]) for each unit increase in the TyG index, the TyG BMI index, and the TyG WC index. When grouped by cutoff values, the risk was reduced by 35.9% (HR 0.641).[0.505,0.814]); 86.7% (HR 0.133).[0.104,0.171]); and 81.6% (HR 0.184).[0.142,0.238]) for groups larger than the cutoff value compared to groups below the cutoff value (Table 3). The TyG BMI index and TyG WC index were not significantly different between subgroups. In the sensitivity analysis, we conducted subgroup analyzes based on healthy physical activity and still found no significant differences between groups (Supplementary Table 6). RCS results show nonlinear associations between TyG BMI index and TyG WC index with sarcopenia, whereas the nonlinear associations between TyG index and sarcopenia were not significant (Fig. 4B-D).

Restricted cubic spline curve for TyG-related index and sarcopenia index hazard ratio. Abbreviations: HR, hazard ratio; CI, confidence interval; TyG, triglyceride glucose index; BMI, body mass index; WC, waist circumference.