Baseline characteristics

The analysis included 15,721 eligible subjects (6820 males, 8901 females). Table 1 presents the baseline characteristics of the subjects according to the TyG index quartiles. Compared with participants in the lowest TyG quartile, individuals in higher quartiles tend to be older, male, more prone to obesity, less educated, earn less, and have more bad habits, such as current smoking and heavy alcohol consumption (all P < 0.001). Furthermore, laboratory findings, including the glycemic markers, fasting insulin, lipid parameters, and liver function, also differed significantly among the TyG index quartiles (all P < 0.001). Dunnett’s post-hoc test revealed that subjects in the second to fourth quartiles of the TyG index had significantly higher laboratory findings than those in the lowest quartile.

Table 1 Comparison of characteristics according to the quartile of TyG index (n = 15,721) Distribution of BP and prevalence of elevated BP, pre-HTN, and HTN according to TyG index quartiles

The distribution of BP according to the quartile of TyG index is shown in Fig. 2A and B. SBP and DBP differed significantly among the TyG index quartiles, and had the lowest values in the lowest TyG index quartile. Both SBP and DBP increased with the TyG index (all P for trend < 0.001).

Fig. 2

Distribution of blood pressure according to the quartile of the TyG index. Mean and standard error of A systolic blood pressure (SBP) and B diastolic blood pressure (DBP) adjusted for survey year, age, and sex. C Percentage distribution of blood pressure categories

Figure 2C shows the percentage distribution of BP categories according to the TyG index quartile. The percentage of participants defined as HTN was highest in the highest TyG quartile and lowest in the lowest TyG quartile (21.5% vs. 4.1%, P < 0.001 among groups). The percentage increased with the TyG index quartile. Similar trends were observed for the participants classified as pre-HTN (32.9% vs. 14.7%).

Similarly, in the subgroup analysis based on the insulin resistance status (Additional file 1: Figure S1), as the TyG index increased, the prevalence of pre-HTN and HTN increased in both the non-insulin and the insulin resistant groups (all P < 0.001).

Independent correlates of blood pressure variability

Table 2 shows the results of multiple regression analysis with stepwise variable selection to identify the aggregate combination of correlates making the greatest contribution to BP changes. Stepwise linear regression revealed that among the 16 entered variables, the most important correlates of SBP were the combination of age, sex, marital status, education level, household income, smoking status, frequency of heavy episodic drinking, family history of hypertension, BMI, FPG, HDL-cholesterol, AST, and TyG index, accounting for 26.43% of the SBP variance in this population (F = 429.47, P < 0.001). Age, sex, household income, smoking status, frequency of heavy episodic drinking, family history of hypertension, BMI, HDL-cholesterol, LDL-cholesterol, ALT, and the TyG index independently affected DBP, explaining 20.80% of the variance in DBP (F = 371.14, P < 0.001). In particular, higher age, BMI and TyG index, and male sex had greater correlations with BP variability. In the subgroup analysis of 2019 data, which also considered fasting insulin and HOMA-IR, similar results were observed.

Table 2 Results of stepwise multiple regression analysis for predictors of blood pressure variability Association of TyG index with elevated BP, pre-HTN and HTN

We used multinomial logistic regression analysis to evaluate the association of the TyG index with the prevalence of elevated BP, pre-HTN, and HTN (Table 3). The ORs of elevated BP, pre-HTN, and HTN increased with the TyG index quartiles (all P for trend < 0.001). Specifically, participants in the highest TyG index quartile had 1.82-fold higher odds of elevated BP (95% CI, 1.50–2.21), 2.95-fold higher odds of pre-HTN (95% CI, 2.62–3.34), and 6.46-fold higher odds of HTN (95% CI, 5.36–7.78) than the lowest TyG index quartile group in the age- and sex-adjusted model. Even after adjusting for conventional risk factors of HTN, such as demographic factors, health behavior (smoking and alcohol drinking), family history of hypertension, and BMI, participants in the highest TyG index quartile were most prominently associated with higher prevalence of elevated BP (OR, 1.52; 95% CI, 1.24–1.87), pre-HTN (OR, 2.22; 95% CI, 1.95–2.53), and HTN (OR, 4.24; 95% CI, 3.49–5.16). We also observed significant dose–response relationships between the continuous TyG index and BP categories.

Table 3 Multinomial logistic regression model for the association of TyG index quartiles with elevated blood pressure, pre-hypertension, and hypertension

In the analyses stratified by age, sex, BMI, and insulin resistance status (Table 4), age significantly modified the association between the TyG index and the prevalence of pre-HTN (P interaction < 0.001) or HTN (P interaction < 0.001), and the associations were more apparent among those who were < 50 years of age. However, the association of the TyG index with BP categories did not differ by sex, except for elevated BP; elevated BP was more prominent in women than in men (P interaction = 0.015). There were also no interactions between the TyG index and BMI or insulin resistance status.

Table 4 Multinomial logistic regression model for the association of TyG index quartiles with elevated blood pressure, pre-hypertension, and hypertension by age, sex, BMI, and insulin resistance status