Remnant cholesterol–inflammation index and depressive symptoms in middle-aged and older adults with study-defined low bone mass: component-specific analysis and supportive clinical corroboration

BackgroundLow bone mass and depressive symptoms commonly coexist in later life, but their shared metabolic–inflammatory profile is poorly characterized. We examined the remnant cholesterol–inflammation index (RCII) within adults aged ≥50 years with study-defined low bone mass, evaluated its component-specific associations, and assessed directional consistency in a separate outcome-enriched clinical sample.MethodsThis cross-sectional analysis used survey-weighted NHANES data. Logistic and linear regression models examined depressive-symptom screening positivity and PHQ-9 scores, respectively. Restricted cubic splines were used to evaluate dose–response associations, and component-specific models jointly included standardized log-transformed calculated remnant cholesterol (RC) and cycle-specific C-reactive protein (CRP). The primary association was examined in an outcome-enriched clinical sample using the fixed NHANES standard-deviation (SD) scale.ResultsAmong 1,743 NHANES participants, 139 screened positive (PHQ-9 ≥10). Each survey-weighted SD increment in ln(RCII) was associated with screening positivity (OR, 1.52; 95% CI, 1.15–2.00; P = 0.004). Odds were higher in the highest versus lowest weighted quartile (OR, 3.00; 95% CI, 1.40–6.43; P for trend = 0.002), with no strong evidence of nonlinearity (P = 0.874). Higher ln(RCII) was also associated with higher PHQ-9 scores (β per SD, 0.38; 95% CI, 0.13–0.63; P = 0.004). In the mutually adjusted component model, the cycle-specific CRP measurement remained associated with screening positivity (OR per SD, 1.44; 95% CI, 1.12–1.84; P = 0.005), whereas calculated RC did not (OR, 1.14; 95% CI, 0.89–1.47; P = 0.284); the direct standardized coefficient contrast was imprecise and nonsignificant (P = 0.179). The direction of association was consistent in the outcome-enriched clinical sample (N = 150; 50 events; adjusted OR per fixed NHANES SD, 3.29; 95% CI, 1.92–5.64; P < 0.001).ConclusionHigher RCII was associated with greater depressive-symptom burden among adults with low bone mass, with supportive directional clinical corroboration. Prospective studies with clinically confirmed outcomes are needed.