Association between serum C-reactive protein and low muscle mass among US adults: Results from NHANES 1999 to 2006.

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Inflammation is hypothesized to be a pivotal factor influencing muscle function, with C-Reactive Protein (CRP) serving as a common biomarker of inflammation. However, the literature pertaining to the relationship between CRP and muscle mass remains scant, particularly among representative adult populations in the United States. The present study aimed to delve into the association between serum CRP levels and muscle mass among American adults, leveraging data from the National Health and Nutrition Examination Survey (NHANES) conducted from 1999 to 2006. A cohort of 13,518 participants, representative of the US adult population, underwent dual-energy X-Ray Absorptiometry (DXA) to assess Appendicular Skeletal Muscle Mass (ASM) and had their CRP levels measured. Muscle mass was defined using ASM adjusted by Body Mass Index (ASM/BMI) criteria. Employing weighted logistic regression models, restricted cubic spline analysis, and subgroup analyses, the authors examined the association between serum CRP and low muscle mass. After meticulously adjusting for various covariates, the present findings revealed a positive association between serum CRP levels and the risk of low muscle mass in American adults (OR = 1.07, 95 % CI 1.01‒1.14, p = 0.016). Notably, an inverse J-shaped relationship was observed, with serum CRP inflection points of 0.273 mg/dL for the overall population, 0.172 mg/dL for males, and 0.296 mg/dL for females. Subgroup analysis further demonstrated that factors such as gender, race, educational level, smoking status, congestive heart failure, stroke, renal weakness/failure, coronary heart disease, diabetes, hypertension, vigorous physical activity, moderate physical activity, and muscle strengthening activities did not significantly impact this positive correlation (all p for interaction values > 0.05). This nationally representative cross-sectional study provides robust evidence of an inverse J-shaped association between serum CRP levels and the risk of low muscle mass in adults in the United States, with a critical inflection point of 0.273 mg/dL. These findings may inform future research and clinical strategies aimed at mitigating the negative effects of inflammation on muscle mass and function in the adult population.