Participant baseline characteristics.

BackgroundAging poses challenges global health and social care systems, with obesity potentially being associated with this process. However, sex differences and the mediating mechanisms underlying this association remain poorly understood. This study investigated sex differences in the associations of visceral adiposity index (VAI) with biological aging (BA) assessed via the Klemera-Doubal method age (KDMAge) and the risk of KDMAge acceleration (KDMAgeAccel), and explored the mediating role of the homeostasis model assessment of insulin resistance (HOMA-IR).MethodsAccording to the National Health and Nutrition Examination Survey (1999–2018), weighted data from 19486 adults were analyzed cross-sectionally. VAI–BA associations were analyzed in the overall population and sex-specific subgroups using multivariable linear and logistic regressions, with nonlinear patterns explored via restricted cubic splines (RCSs) and threshold analyses. Mediation analyses quantified the mediating effects of HOMA-IR.ResultsVAI correlated positively with BA overall. However, females showed stronger associations than males for each 1-unit VAI increase with KDMAge elevation (βfemale = 1.02, 95% CI: 0.81–1.23; βmale = 0.59, 95% CI: 0.42–0.75) and KDMAgeAccel risk (ORfemale = 1.22, 95% CI: 1.17–1.28; ORmale = 1.10, 95% CI: 1.07–1.13), with all associations remaining significant (P Pnonlinear ConclusionVAI showed a significant positive association with BA, with females demonstrating a stronger association strength and males showing a greater proportion of the association mediated through HOMA-IR.