The prevalences of CKD and albuminuria was positively correlated with the TyG index level in this cross-sectional investigation of 18,078 adults. Additionally, we discovered a J-shaped connection between the TyG index and CKD in the 41–60 age range (K = 8.21). If, that is, the TyG index was greater than 8.21, the prevalence of CKD in the 41–60 age group of American participants increased significantly. There was no discernible impact of population differences on the relationship between the TyG index and low-eGFR, albuminuria, and CKD, according to subgroup analysis and interaction testing. Additionally, in comparison to other markers (LAP, VAI, and TyG-BMI index), the TyG index may have greater discriminative power and accuracy in predicting CKD and albuminuria.

In several populations and regions, the link between the TyG index and CKD has been researched [23,24,25]. One study found a connection between a rise in the TyG index and deteriorating kidney function in senior Chinese persons [26]. The TyG index and ESKD (end-stage renal disease) were found to be significantly correlated in cohort research from Austria [12]. In a cohort analysis of 11,712 patients in Japan, the TyG index was found to have a positive relationship with CKD [10]. In China, the TyG index and CKD of hypertension patients were positively associated [11]. A higher TyG index was linked to a higher prevalence of CKD and albuminuria, according to US studies [13, 14]. Our study has a number of advantages over earlier studies as well. Firstly, in the US population of people aged 41–60, which has received less attention in other studies on kidney health in middle-aged adults, our study discovered for the first time a J-shaped link between the TyG index and CKD. Secondly, whereas earlier research on the connection between low-eGFR and the TyG index has produced contentious findings, our analysis of data on US adults revealed no significant connection between the two [10, 13, 26, 27]. Thirdly, we explored territory by conducting ROC analyses to assess the predictive abilities of the TyG index, LAP, VAI, and TyG-BMI index for CKD, albuminuria, and low-eGFR in US adults. This is a fundamental difference from previous studies. Additionally, our study delved into the TyG index’s predictive significance for cardiovascular disease (CVD) prevalence in US adults. This aspect, previously explored primarily for its prognostic implications, adds another layer to our understanding [28, 29].

Our study, in addition to showing a positive correlation between TyG index levels with CKD, demonstrated a J-shaped link between the two in the group of people aged 41–60 (K = 8.21). The twos had a negative correlation, although it was not statistically significant, on the left side of the breakpoint. Nonetheless, every unit increase in the TyG index was linked to a 5.04-fold rise in the prevalence of CKD on the right side of the breakpoint. Therefore, Americans aged 41–60 with a TyG index > 8.21 should pay close attention to their kidney health. TyG index and CKD have been established in earlier research to have a nonlinear association in patients with impaired glucose metabolism and hypertension [30]. A non-linear association between the TyG index and the prevalence of diabetic nephropathy was also discovered by Shang et al. [31]. However, we need more prospective studies to confirm our findings.

According to our research, the TyG index and albuminuria are positively and nonlinearly correlated in US people. The link was seen on both sides of a breakpoint (K = 8.72), with a high positive correlation on the right side and a much weaker positive correlation on the left. That is, the prevalence of albuminuria considerably rises when the TyG index is higher than 8.72. Nonlinear relationships between the TyG index and other diseases have been discovered in prior research. Jiang et al. found a nonlinear correlation between the TyG index and the prevalence of kidney stones [32]. Adult US deaths from cardiovascular and all-cause were shown to have a nonlinear relationship with the TyG index by Liu et al. [33]. The relationship between low-eGFR and the TyG index in previous studies remains controversial [10, 13, 26, 27]. We could not find any relationship between low-eGFR and the TyG index. We believe that different results can be obtained from different demographic characteristics, including population, race, area, sample size, and eGFR calculation method.

IR has been demonstrated to have a significant correlation with CKD [6, 7]. However, the gold standard test for diagnosing IR can be difficult to perform in clinical settings [8]. TyG index, as a simple and feasible IR indicator, has been shown to be significantly better than other traditional IR indicators. Research indicates that the TyG index outperforms the VAI and lipid accumulation product index (LAPI) in predicting CKD occurrence [34]. In our study, we also examined the TyG index’s superiority. ROC analysis showed that the TyG index was a more reliable indicator of CKD and albuminuria than other indicators (LAP, VAI, and TyG-BMI index). To sum up, the TyG index has a lot of potential for clinical use in CKD prediction and might be a more straightforward and accurate IR indicator.

CKD was more likely to occur in female participants, according to our subgroup analysis (Males: OR = 3.62, 95% CI 1.37, 9.53; Females: OR = 4.36, 95% CI 1.88, 10.12). This result has been supported by earlier research [10, 34, 35]. However, the fundamental cause of the sex gap is yet unknown, necessitating additional research. Importantly, the independent associations between the TyG index and CKD, albuminuria, or low eGFR persisted across age, sex, BMI, hypertension, and diabetes. These associations may be applicable to diverse populations, reinforcing the adverse impact of the TyG index on renal function.

Inflammation and oxidative stress brought on by IR may be the basis for the relationship between the TyG index and CKD. IR inhibits the insulin signaling pathway, causes a rise in monocyte chemoattractant protein-1 (MCP-1) synthesis, and encourages inflammation in adipose tissue. Tumor necrosis factor (TNF) -alpha and interleukin-6 (IL-6) are two pro-inflammatory cytokines that are produced when macrophages are activated by inflammatory stimuli in adipose tissue [36, 37]. Endothelial dysfunction is related to CKD and is facilitated by TNF-alpha and IL-6 [10, 38]. Additionally, oxidative stress and IR are related [38]. The activation of nuclear factor erythroid-2-related factor-2 (Nrf-2), which defends renal tissue, might be compromised by oxidative stress and inflammation [39]. The precise mechanisms underlying this relationship, however, need more research.

CKD increases the risk of various adverse outcomes, especially CVD [40]. As a result, we looked into the possibility of a connection between CVD and the TyG index. According to our findings, for every unit rise in the TyG index, the prevalence of CVD increased by 61%. Similar findings were noted in earlier research [28, 41, 42]. Prior research also revealed that the TyG index outperformed VAI as a predictor of CVD risk [43]. In addition, our research revealed that, when compared to the LAP, VAI, and TyG-BMI index, the TyG index had the greatest AUC value for predicting CVD. Therefore, we need to pay equal attention to the importance of the TyG index for renal and cardiovascular health in US adults.

The advantages of our research are numerous. Initially, the NHANES data is a nationwide population-based survey. The second reason is that our study is more reliable and representative because of its large sample size and adjustment for confounding factors. However, there are several shortcomings in our investigation. The cross-sectional design, for example, made it unable to show a causal relationship between the TyG index and CKD. Second, we are unable to completely exclude the influence of additional potential confounding variables, even after adjusting for a number of significant confounders. Third, because the US population survey NHANES is cross-sectional in nature, extrapolating our findings to other ethnic groups or the larger population may prove difficult.