Abstract
BACKGROUND: The sarcopenia index (SI) is an accessible biomarker of muscle mass, yet its specific association with osteoarthritis (OA) remains unclear. This study aimed to evaluate this relationship both cross-sectionally and longitudinally in a large, representative cohort. METHODS: We analyzed data from the U.S. Health and Retirement Study, including 8720 participants for cross-sectional analysis (2016) and a longitudinal cohort of 3,745 participants free of OA at baseline followed through 2020. Baseline SI was the exposure, and self-reported prevalent and incident OA were the outcomes. Multivariable-adjusted logistic regression was used to assess the association with prevalent OA and Cox proportional hazards models were used for incident OA. The dose-response relationship was analyzed employing restricted cubic splines, and sensitivity analyses were conducted to confirm the stability of the findings. RESULTS: The cross-sectional analysis demonstrated an inverse association between SI and prevalent OA. After multivariable adjustment, each 1-standard deviation (SD) increase in SI was associated with a lower likelihood of OA (OR = 0.921; 95% CI 0.866-0.980); a similar association was found for the highest versus lowest SI quartile (OR = 0.753; 95% CI 0.638-0.887). In the prospective analysis, 676 of 3,745 participants developed incident OA over a median 4.0 years. A higher baseline SI was associated with a lower likelihood of developing OA, both when assessed per 1-SD increase (HR = 0.891; 95% CI 0.813-0.977) and for the highest versus lowest quartile (HR = 0.771; 95% CI 0.597-0.995). CONCLUSION: Higher levels of the SI were significantly associated with a reduced risk of OA. Further investigation is warranted to confirm this association and explore the underlying mechanisms.