BMI-specific nonlinear associations and threshold effects of the atherogenic index of plasma on incident prediabetes: insights from 100473 Chinese adults

Background Emerging evidence suggests that the atherogenic index of plasma (AIP), a simple marker of lipid-related metabolic risk, may relate to dysglycemia in a nonlinear fashion. However, whether this association differs across body mass index (BMI) categories, particularly in terms of nonlinear risk patterns and thresholds, remains unclear. Methods We analyzed data from 100,473 Chinese adults who underwent baseline health examinations and had baseline FPG < 5.6 mmol/L. Because HbA1c and OGTT data were unavailable, the outcome was defined as FPG-defined incident prediabetes (5.6-6.9 mmol/L). Participants were classified into underweight, normal weight, overweight, and obesity groups according to Chinese BMI criteria. Restricted cubic spline (RCS) and Cox regression were used to evaluate BMI-specific associations between AIP and prediabetes risk and to test for interaction by BMI. Results During a median follow-up of 3.0 years, 12,371 participants developed FPG-defined incident prediabetes. A significant interaction between AIP and BMI was observed (P for interaction < 0.001). BMI-stratified analyses showed that AIP was associated with FPG-defined prediabetes risk only among normal-weight and overweight participants, but not among underweight or obese participants. RCS analyses further identified nonlinear associations in these two BMI groups, with model-derived inflection points at AIP = -0.20 in normal-weight individuals and AIP = 0.057 in overweight individuals. Conclusion BMI modified the association between AIP and FPG-defined prediabetes risk. Significant nonlinear and threshold-dependent associations were observed only in normal-weight and overweight Chinese adults.