Association of dynapenic obesity defined by sagittal abdominal diameter and relative grip strength with all-cause mortality: a prospective cohort study.

BACKGROUND: Dynapenic obesity is associated with increased mortality, but definitions based on BMI, waist circumference, or absolute grip strength may misclassify adiposity and muscle weakness. We examined whether sagittal abdominal diameter (SAD) combined with relative grip strength identifies a high-risk phenotype and explored potential explanatory pathways. METHODS: This prospective cohort included 5674 US adults followed for a median of 6.75 years. Participants were classified as Normal, Abdominal Obesity, Dynapenia, or Dynapenic Obesity based on SAD and relative grip strength. Survey-weighted Cox models using age as the time scale estimated hazard ratios (HRs) for all-cause mortality. Exploratory mediation analyses estimated the proportions of the observed association statistically explained by systemic immune-inflammation index (SII) and HbA1c. Joint analyses cross-classified phenotypes by biomarker levels. RESULTS: During follow-up, 373 deaths occurred. Dynapenic Obesity was associated with the highest mortality risk (HR 1.97; 95% CI 1.41-2.75), followed by Dynapenia (HR 1.60; 95% CI 1.11-2.30), whereas Abdominal Obesity was not significantly associated with mortality. SII and HbA1c statistically explained 5.8% (P = 0.041) and 13.7% (P = 0.006), respectively, of the observed dynapenic obesity-mortality association. Participants with Dynapenic Obesity and elevated biomarkers had higher mortality risks (HR 3.11 for high SII; HR 2.53 for high HbA1c). Findings were robust across sensitivity analyses. CONCLUSIONS: Dynapenic obesity, defined using SAD and relative grip strength, was associated with nearly twice the risk of all-cause mortality. SII and HbA1c may help characterize mortality risk in individuals with dynapenic obesity.