From 2006 to 2009, 126,847 subjects from the Kailuan community were included in the first health experience. Following a sequence of exclusion criteria, a total of 117326 participants were incorporated within the current investigation (Additional file 1: Figure S1). Table 1 shows the clinical and laboratory features at baseline based on the quartiles of CMI level. In contrast to those within the lowest quartile group, individuals exhibiting a greater CMI have been shown to possess certain characteristics such as advanced age, male gender, increased obesity as indicated by higher BMI and WC, and a higher prevalence of AP among participants. Similarly, significant variations in biological characteristics were noted across the groups. FPG, TG, and LDL-C levels of the subjects within the highest quartile of CMI were found to be considerably elevated compared to those in the first quartile. Furthermore, it was shown that the groups with elevated CMI levels exhibited a greater incidence of comorbidities, including diabetes,hypertension,and cholelithiasis.
The occurrence of AP in the quartile groups of CMI
Over the course of a mean follow-up period of (12.59 ± 0.98) years, 401 cases of AP occurred, with 72,97,88,144 new cases of AP in each CMI quartile group, and the incidence densities were 1.75, 2.37, 2.25, and 3.55/10 000 person-years, respectively. Incidence density and cumulative incidence rates of AP increased with CMI. Figure 1 presents the cumulative incidence rates in the quartile groups of CMI level.
Association of CMI, LAP, WTI and BMI with the risk of AP
Baseline CMI, LAP, and WTI quartile groups have been evaluated via COX proportional hazards regression model with AP, and Table 2 presents the results. Taking the lowest quartile of CMI, LAP, and WTI as the reference without adjusting for other confounding factors, the results showed that the HRs (95% CIs) within the second, third, and greatest quartile of CMI have been 1.35(0.99–1.83), 1.29(0.94–1.76), and 2.03(1.53–2.69), respectively. The HRs (95% CIs) within the second, third, and greatest quartile of LAP were 1.26 (0.92–1.73), 1.41 (1.04–1.92), and 2.14 (1.61–2.85), respectively. The HRs (95% CIs) in the second, third, and highest quartile of WTI have been 1.14 (0.83–1.57), 1.41 (1.04–1.92), and 2.24 (1.69–2.97), independently. According to the BMI classification standard defined by “Chinese Expert Consensus on Medical nutrition treatment of overweight/obesity” , the observation population was separated into the normal weight group (BMI < 24 kg/m2), overweight group (BMI 24–28 kg /m2), and obesity group (BMI ≥ 28 kg/m2). Taking the Normal weight group as a reference, the adjusted HRs (95% CIs) within the overweight group and obese group BMI have been 1.14 (0.91–1.43) and 1.64(1.27–2.12). The highest CMI, LAP, and WTI quartiles were associated with the highest risk for AP. Results were comparable within an age-,sex- and BMI-adjusted model and in a multivariable-adjusted model. According to the relevant factors of the multivariate cox regression analysis of CMI, the nomogram was constructed (Fig. 2).
Stratified by age, using the lowest quartile of CMI, LAP and WTI as controls, the HRs (95% CIs) of AP in age ≤ 40 years,after adjusting for multivariable factors, the highest quartile of CMI, LAP and WTI were 5.94 (2.42,14.55), 6.41(2.68,15.34), and 7.20(2.89,17.90), respectively. The HRs (95% CIs) of AP in the highest quartile of CMI, LAP, and WTI were 1.62(1.08,2.42), 1.73(1.13,2.64), and 1.96(1.32,2.93) in the 40–60 years group, respectively. The HRs (95% CIs) of AP in age ≥ 60 years, the highest quartile of CMI, LAP, and WTI were 1.15(0.63,2.09), 1.19(0.62,2.32), and 1.11(0.61,2.04), respectively.In the normal weight group (BMI < 24 kg/m2) as the control group, age ≤ 40 years, after adjusting for multivariable factors, the HR(95% CIs) of AP occurrence in the obesity group (BMI ≥ 28 kg/m2) was 3.21(1.64,6.30). When the age was between 40 and 60 years, the HR(95% CIs) of AP in the obesity group was 1.37(0.96,1.94). The HR(95% CIs) of AP in the obesity group was 1.42(0.84,2.40) when the age was ≥ 60 years.Stratified by gender, the HRs (95% CIs) of AP in the highest quartile of CMI, LAP, WTI and obesity group were 2.50(1.04,6.02), 2.25(0.85,5.94), 3.76(1.50,9.40), and 1.81(0.94,3.50), respectively.The HRs (95% CIs) of AP in men with the highest quartile of CMI, LAP, WTI and obesity group were 1.70(1.23,2.36), 1.93(1.36,2.74), 1.86(1.34,2.57) and 1.55(1.16,2.07), respectively.The results are detailed in Table 3.
Incremental predictive value of BMI and CMI, LAP and WTI in AP
We conducted a comparative analysis of the prognostic value of BMI and CMI, LAP, and WTI in AP (Table 4). The C-statistics related to BMI exhibit enhancement upon the inclusion of CMI (from 0.546 to 0.607, P < 0.001), LAP (from 0.546 to 0.597, P < 0.001), and WTI (from 0.546 to 0.593, P < 0.001), respectively. The discriminatory capacity and risk reclassification of CMI, LAP, and WTI were shown to be significantly superior to BMI. The combined discrimination enhancement for CMI, LAP, and WTI was 0.321% (95% CI, 0.290%–0.351%; P < 0.0001), 0.318% (95% CI, 0.289%–0.349%; P < 0.0001), 0.302% (95% CI, 0.271%–0.333%; P < 0.0001), independently. The corresponding net reclassification index for CMI, LAP, and WTI was 1.975% (95% CI, 1.953%–1.997%; P < 0.0001), 1.935% (95% CI, 1.901%–1.969%; P < 0.0001), and 1.930% (95% CI, 1.894%–1.966%; P < 0.0001), independently. Among them, the inclusion of integrated impact of BMI and CMI can significantly also enhance the C statistics, the discriminatory capacity, and risk reclassification. This result provides substantial proof supporting the assertion that the incremental effect of CMI, LAP, and WTI on the predictive value of AP is higher than that of BMI, especially CMI.