The association between life’s crucial 9 and osteoarthritis in US adults: the mediating role of central adiposity

BACKGROUND: Osteoarthritis (OA), a prevalent degenerative joint disorder characterized by progressive cartilage loss and secondary low-grade inflammation, is recognized to be associated with cardiovascular diseases (CVD). Building upon the cardiovascular assessment framework of Life’s Essential 8 (LE8), emerging guidelines propose the integration of psychological health metrics (Patient Health Questionnaire-9, PHQ-9) into the expanded Life’s Crucial 9 (LC9) model. While LC9 demonstrates cardiovascular predictive capacity, its role in OA pathogenesis remains inadequately substantiated. METHODS: This study analyzed data from 21,196 National Health and Nutrition Examination Survey (NHANES) participants (2005–2018). Survey-weighted logistic regression, weighted quantile sum (WQS) regression, and restricted cubic splines (RCS) assessed the LC9–OA association with prespecified confounders. Subgroup analyses were also conducted. Mediation analysis was performed to assess the potential mediating effects of central adiposity, specifically the Body Roundness Index (BRI) and Waist-to-Height Ratio (WHtR). RESULTS: Each 10-point higher LC9 was associated with lower odds of OA (OR = 0.79; 95% CI 0.74–0.84; P < 0.001). Interactions suggested stronger inverse associations in younger adults (≤ 40 years) and in women. WQS regression identified body mass index (33.00%), nicotine exposure (28.40%), and depressive symptoms (13.60%) as the largest contributors to OA risk. While LC9 and LE8 showed comparable discriminatory accuracy (AUC: 0.616 vs. 0.607, P = 0.077), LC9 demonstrated superior reclassification performance (NRI = 0.02, P = 0.002). Mediation analyses indicated that central adiposity accounted for a substantial proportion of the association (WHtR 39.63%; BRI 37.82%). Findings were robust in analyses restricted to adults ≥ 40 years. CONCLUSION: Higher LC9 scores were associated with lower odds of OA, partly mediated by central adiposity. Cardiovascular health metrics that incorporate psychological health may be relevant to OA burden. Prospective studies are needed to establish temporality and causal pathways.