MRI reveals the hierarchical organization of abdominal biological aging from shared burden to disease-specific organ engagement

Multi-organ biological aging is often represented as parallel organ-specific clocks, but how age gaps should be interpreted within an anatomically coupled imaging system remains unclear. Applying end-to-end deep learning to abdominal Dixon MRI from 67,130 UK Biobank participants, we show that abdominal biological aging is hierarchically organized across eight compartments. Compartment age gaps were positively intercorrelated (mean pairwise r = 0.42), and their unweighted mean--the Overall Aging Gap (OAG)--broadly stratified all 15 prespecified prospective endpoints, including 14 incident diseases and all-cause mortality (hazard ratios 1.15-1.49 per s.d.; mortality HR = 1.41 per s.d.). After accounting for OAG, compartment-level associations became sparser and more anatomically coherent, indicating disease-specific refinement beyond the shared axis. Healthier lifestyle was associated with lower risk within accelerated-aging strata. These findings establish a hierarchical framework for interpreting abdominal MRI age gaps: OAG stratifies broad prospective risk, whereas axis-conditional compartment engagement refines disease-specific anatomical vulnerability.