Association of the atherogenic index of plasma–frailty index composite with incident type 2 diabetes: a prospective cohort study from CHARLS

The atherogenic index of plasma (AIP) reflects lipid-related metabolic abnormalities, whereas the frailty index (FI) captures cumulative physiological deficits. However, the association of a composite index integrating AIP and FI with incident type 2 diabetes mellitus (T2DM) remains unclear. This prospective cohort study included 6,885 participants aged ≥ 45 years without diabetes at baseline from the China Health and Retirement Longitudinal Study (CHARLS). Cox proportional hazards models and restricted cubic spline (RCS) analyses were used to examine the association between AIP-FI and incident T2DM. During a median follow-up of 9.0 years, 746 participants developed incident T2DM (10.8%). In the fully adjusted model, each 1-SD increase in AIP-FI was associated with a 23% higher risk of incident T2DM (HR 1.23; 95% CI: 1.15–1.32). Compared with Q1, Q4 was associated with a higher risk of incident T2DM (HR 1.72; 95% CI: 1.40–2.11). RCS analyses indicated a significant nonlinear association between AIP-FI and incident T2DM (all P for overall < 0.001; all P for nonlinearity < 0.001). Higher AIP-FI was associated with an increased risk of incident T2DM among middle-aged and older Chinese adults. AIP-FI may serve as a readily accessible composite indicator for identifying individuals at elevated risk of T2DM.