Inflammatory and Nutrition‐Glucose Metabolic Factors in Relation to Sarcopenia Prevalence Among US Adults: Evidence From NHANES 2015–2018

BACKGROUND: The relationship between chronic inflammation (CRP, WBC), metabolic disorders (vitamin D, HbA1c), and sarcopenia in the US adult population has been rarely explored. This study integrates these indicators, aiming to provide a basis for the early identification and precise intervention of high-risk populations. METHODS: A cross-sectional study was conducted using participants from NHANES 2015-2018. Logistic regression analysis, restricted cubic splines (RCS), receiver operating characteristics (ROC) curves, and subgroup analyses were applied to evaluate associations between inflammatory and metabolic indicators, their combinations, and sarcopenia. RESULTS: Sarcopenia risk was significantly positively correlated with CRP, WBC, HbA1c, and their combination marker CRP-HbA1c (all p < 0.05), while vitamin D alone and WBC-VitD combination had no significant effects. CRP emerged as the strongest inflammatory predictor (Q4 OR = 5.02-5.67, p < 0.001), and CRP-HbA1c showed optimal predictive performance (AUC = 0.796, 95% CI: 0.774-0.819; Q4 OR = 5.95-7.19). HbA1c had clear independent effects (Q4 OR = 2.00-3.24); vitamin D showed protective effects only in adjusted models (Q4 OR = 0.51). RCS revealed nonlinear relationships for CRP and WBC (p-nonlinear < 0.05). Notably, BMI significantly modulated CRP-HbA1c effect strength (interaction p = 0.034). CONCLUSION: Inflammatory markers (CRP, WBC) and metabolic indicator (HbA1c) synergistically drive sarcopenia pathogenesis. CRP-HbA1c has superior predictive value. Higher levels of vitamin D play a significant protective role against sarcopenia. Nonlinear analysis confirms dose-dependent positive correlations for CRP and WBC (p-nonlinear < 0.05). These findings emphasize that chronic inflammation and poor blood glucose control are key mechanisms in the development of sarcopenia.