The Role of hs-CRP and Systemic Immune–Inflammation Index in Sarcopenia and Sarcopenic Obesity in Young Populations: Results from the National Health and Nutrition Examination Survey 2015-2018

INTRODUCTION: Inflammation is critical in developing sarcopenia and sarcopenic obesity in older adults, yet evidence in younger populations remains scarce. This study examines associations of high-sensitivity C-reactive protein (hs-CRP) and systemic immune-inflammation index (SII) with sarcopenia and sarcopenic obesity among US adults. METHODS: By using data from the 2015-2018 cycles of the National Health and Nutrition Examination Survey (NHANES), we conducted this cross-sectional analysis of adults aged ≥18 years. Overall, 4,870 participants were included, and both hs-CRP and SII values were divided into quartiles. Multivariable logistic regression was used to analyze the associations of hs-CRP and SII with both sarcopenia and sarcopenic obesity. Interaction tests were conducted to confirm model stability and identify individuals at high risk of developing sarcopenia. RESULTS: Multivariable logistic regression showed positive associations of SII and hs-CRP with sarcopenia and sarcopenic obesity. Compared to participants in the lowest SII quartile, those in the highest SII quartile had an increased odds of sarcopenic obesity (odds ratio [OR] 1.82, 95% confidence interval [CI] 1.24-2.67, p < 0.0022) and sarcopenia (OR 1.94, 95% CI 1.41-2.68, p < 0.0001). Participants in the highest hs-CRP quartile were also associated with significantly increased odds of sarcopenic obesity (OR 24.69, 95% CI 8.99-67.78, p < 0.0001) and sarcopenia (OR 6.09, 95% CI 3.89-9.53, p < 0.0001). DISCUSSION: Our findings extend the conclusions of previous studies conducted in older populations by demonstrating that systemic inflammation is also positively associated with the incidence of sarcopenia and sarcopenic obesity in younger adults. This finding suggests that individuals with an elevated inflammation level are more likely to develop these conditions. To our knowledge, this is the first study to report these associations in a younger adult population, offering reliable data and practical options for screening sarcopenia in high-risk community groups by using routine clinical tests. CONCLUSION: These findings support the potential of hs-CRP and SII as individual or combined screening tools to assess sarcopenia and sarcopenic obesity risk in community or large-population settings.