Nonlinear and Age-Specific Associations Between Atherogenic Index of Plasma and Differential Cardiovascular Risk Profiles in US Adults.

Background: The association between the atherogenic index of plasma (AIP) and different cardiovascular disease (CVD) outcomes remains insufficiently studied. Methods: Data from 16,302 US adults in NHANES 2005-2020 were analyzed. CVD outcomes included congestive heart failure, coronary heart disease, angina, heart attack, and stroke. Multivariable logistic regression models assessed the linear association between AIP and CVD. Restricted cubic splines were used to examine potential nonlinear relationships, whereas threshold effect analysis identified inflection points. Stratified analyses explored interactions between AIP and covariates. Results: Compared with the lowest quartile, the highest AIP quartile was associated with increased odds of overall CVD (OR = 1.73, 95% CI = 1.20-2.52, p for trend = 0.001), coronary heart disease (OR = 2.20, 95% CI = 1.20-4.25, p for trend = 0.013), and heart attack (OR = 2.53, 95% CI = 1.42-4.74, p for trend = 0.008). A U-shaped relationship was observed between AIP and congestive heart failure (p overall = 0.0004, p nonlinear = 0.002), with a sharp odds increase when AIP exceeded 0.22 (OR = 3.40, 95% CI = 1.81-6.38, p < 0.01). Subgroup analysis revealed a significant age interaction: Among adults younger than 55 years, each AIP increment was associated with higher odds of CVD (OR = 2.53, 95% CI = 1.60-3.98, p = 0.001), heart attack (OR = 2.58, 95% CI = 1.21-5.54, p = 0.014), and stroke (OR = 2.98, 95% CI = 1.44-6.17, p = 0.003). Conclusion: Elevated AIP is an independent predictor of CVD, coronary heart disease, and heart attack, particularly in younger adults (< 55 years). A U-shaped relationship was identified between AIP and congestive heart failure. These findings highlight AIP as a valuable biomarker for CVD risk assessment and emphasize the importance of age-specific intervention strategies targeting different CVD outcomes.