Associations of atherogenic index of plasma and its related obesity‑composite indices with cardiometabolic multimorbidity across glycemic states: A prospective cohort study of Chinese middle‑aged and older adults.

AIMS: To investigate associations of atherogenic index of plasma (AIP) and seven obesity-composite indices with cardiometabolic multimorbidity (CMM) across glycemic states. METHODS: We included 7,974 participants from the China Health and Retirement Longitudinal Study (CHARLS). Cox regression, restricted cubic splines (RCS), receiver operating characteristic (ROC) analyses, net reclassification improvement (NRI), and integrated discrimination improvement (IDI) assessed associations and incremental predictive value of AIP-related indices for CMM. RESULTS: Over 9 years, 988 CMM cases occurred. All indices were positively associated with CMM in normal glucose regulation (NGR) and prediabetes (Pre-DM) groups (HRs 1.64-2.03). In diabetes (DM), point estimates were similar in magnitude, with wider confidence intervals reflecting lower statistical precision. AIP-CVAI showed strongest discrimination (AUC 0.594-0.640), though its absolute discriminatory ability was modest and the incremental gains over traditional risk factors were small (IDI < 1.5 %). Formal interaction tests were non-significant for all indices (all P for interaction > 0.05), indicating consistent associations across glycemic states. CONCLUSIONS: AIP-obesity indices, particularly AIP-CVAI, are independently associated with CMM risk, with consistent effects across glycemic states. Given their modest discrimination and small incremental predictive value, these indices should be regarded primarily as population-level risk-stratification aids rather than individual-level clinical prediction tools.