Association between the sarcopenia index and osteoarthritis: a cross-sectional and longitudinal study

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.

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.

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).

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.