Correlations of the Atherogenic Index of Plasma with Cardiometabolic Comorbidities: The Mediating Role of Physical Function Impairment

Background: Cardiometabolic multimorbidity (CMM) poses an increasing public health challenge among aging populations. The atherogenic index of plasma (AIP), a metabolic disorder-associated lipid indicator, exhibits unclear connections with CMM and its underlying mechanisms. Methods: This cross-sectional study investigated 10,878 participants (mean age 59.8 years) from the China Health and Retirement Longitudinal Study (CHARLS). CMM was delineated as $ \geq 2 $ cardiometabolic conditions, whereas AIP was computed as the $\log(\text{TG}/\text{HDL-C})$ ratio. A combination of Logistic, and piecewise regressions was employed for examining associations and nonlinear relationships. The impact of physical function impairment was evaluated by mediation analysis. Results: The highest AIP quartile (Q4) group faced a 3.04-fold elevated CMM risk in contrast to the lowest quartile (Q1) group (OR=3.04, 95% CI: 2.51–3.68, P $<$0.001). A substantial nonlinear association was identified, with an AIP value of 0.96 serving as the threshold. Each unit rise in AIP corresponded to a 4.19-fold heightened risk of CMM (OR=4.19, 95% CI:3.36–5.23, P $<$0.001)below this threshold, while beyond it, statistically insignificant association was noted (OR=0.86, 95% CI: 0.41–1.82, P $=$0.692). According to mediation analysis results, physical function impairment contributed to 7.2% ( P $=$0.026) of the AIP–CMM association. Conclusion: An AIP threshold of 0.96 may serve as a critical cut-off for stratifying CMM risk. Physical function impairment partially mediates the influence of AIP on CMM, implying that concurrent management of lipid metabolism and physical function can help synergistically mitigate the progression of CMM. our findings offer fresh perspectives into the precise prevention and intervention of CMM in aging populations.