Longitudinal multicohort evidence for bidirectional diabetes arthritis links in older adults.

Diabetes mellitus and arthritis frequently co-occur in older adults, but whether they causally reinforce each other and through which mechanisms remain unclear. We used harmonized longitudinal data from three nationally representative cohorts across China (CHARLS), the United States (HRS), and Europe (SHARE) to test bidirectional relationships between diabetes and arthritis in late life. Cross-lagged panel models over multiple waves quantified reciprocal effects, prespecified mediation analyses evaluated 21 biologically and clinically motivated mediators, and the NOTEARS algorithm probed data-driven causal network structure. Across all cohorts, diabetes consistently increased subsequent arthritis risk and to a lesser extent, arthritis increased subsequent diabetes risk, with effects robust across demographic and clinical subgroups. C-reactive protein, grip strength, and HbA1c emerged as the dominant mediators, linking metabolic, inflammatory, and functional pathways. These findings support viewing diabetes and arthritis as mutually reinforcing conditions that share modifiable upstream mechanisms, motivating integrated prevention and management strategies in aging populations.