Baseline Characteristics of Participants:
Table 1 presents the initial characteristics of each participant. The study had a total of 10,247 individuals, at a median age of 47.44 years. Of the participants, 49.76% were male and 50.24% were female. The participants were divided into Q1-Q4 groups based on their AIP quartiles. Significant differences were observed in age, gender, race, education level, PIR, marital status, BMI, drinking status, smoking status, hypertension, cholesterol prescription, diabetes, ALT, AST, SUA, creatinine, and total cholesterol among the highest quartile (Q4) of AIP compared to other subgroups (all P < 0.05).
Relationship Between AIP and SUA:
The findings of the multivariate regression analysis between AIP and SUA are displayed in Table 2. The study's findings suggest that the chance of SUA occurring increases with plasma's Atherogenic Index score. In the unadjusted model 1, a positive connection was found between AIP and SUA (β = 1.2995, 95% CI: 1.21 - 1.37, P < 0.001). After adjusting for age, gender, and race, there remained a significant positive association in model 2 (β = 1.0495, 95% CI: 0.97 - 1.12, P < 0.001). The positive link persisted in the entirely adjusted model 3 (β = 0.6895, 95% CI: 0.60 - 0.76, P < 0.001). The association between AIP and SUA remained statistically significant even when we categorized AIP into quartiles instead of treating it as a continuous variable. Individuals in the upper quartile of AIP exhibited a 0.61 μmol/L increase in SUA compared to those in the smallest quartile (model 3, β = 0.6195, 95% CI: 0.54 - 0.68) while accounting for confounding variables. Furthermore, the outcomes utilizing generalized additive models and smooth fit curves hint to a non-linear correlation between SUA risk and AIP.
Non-Linear Relationship:
The study's findings, as shown in Figure 2, demonstrate a non-linear relationship association between AIP with SUA, as indicated by the GAM and smooth fitting of curves analysis. The log-likelihood ratio test revealed a P value of less than 0.001 when comparing the linear regression model and the two-piecewise linear regression model, This suggests that the two-piecewise linear regression model provides a superior fit to the data.
The results of the investigation, employing the recursive algorithm and two-piecewise linear regression model, are presented in Table 3. The inflection point of the inverted U-shaped correlation between AIP (atherogenic index of plasma) and SUA (serum uric acid) was determined to be 0.87. The effect size of 0.81 (95% CI: 0.72 - 0.89) and P value of less than 0.001 on the left side of the inflection point show a strong favorable connection. Nonetheless, there was a substantial negative correlation between AIP and SUA on the right side of the second inflection point. The study findings reveal that there was a positive association between AIP levels and SUA levels. The effect size was -0.55 (95% CI: -0.91 - 0.18) and the statistical significance was shown by a P value of 0.003.
Subgroup Analysis:
In order to examine the link between AIP and SUA levels more thoroughly and provide data, a subgroup analysis was performed. So as to evaluate the effects of various variables, interaction tests were also performed. AIP and SUA consistently exhibited a positive correlation in the subgroup analysis results, demonstrating the stability of the link between the two variables. Interestingly, there was no significant interaction found for age, gender, BMI, diabetes, or hypertension, indicating that these variables are not necessary for this link to exist (interaction P > 0.05 for all).