Inverse association between triglyceride-glucose index and maximal oxygen uptake in US young and middle-aged...

The triglyceride-glucose (TyG) index has been linked to impaired cardiovascular fitness (CVF). However, the available evidence regarding the direct relationship between the TyG index and maximal oxygen uptake (VO₂max) is limited. This study aims to investigate the association between the TyG index and VO₂max.

We conducted a retrospective cross-sectional study involving 3,571 participants who completed a CVF examination as part of the National Health and Nutrition Examination Survey (NHANES) 1999-2004. Data on triglycerides, glucose, and VO₂max were collected from all participants. The TyG index was calculated using the formula: Ln[triglyceride (TG)(mg/dl) × fasting plasma glucose (FPG)(mg/dl)/2]. Linear regression analysis was utilized to substantiate the research objectives.

The complex sampling design and mobile examination center sample weights were considered. In multivariable linear regression analyses, each 1 unit increase in the TyG index was associated with a decrease in VO₂max [β = -1.24, 95% CI (-1.97, -0.51), p = 0.002] when expressed as a continuous variable, independent of confounders. The TyG index was converted into a categorical variable based on four quartiles. Compared with the lowest TyG quintile (Q1: 6.750-7.887), the fully adjusted β for Q4 (8.672-12.481) was -1.91 (95% CI: -3.24, -0.57, p < 0.007). A significant interaction (p = 0.007) between sex and the TyG index for VO₂max was found in the population using subgroup analysis. The results of the sensitivity analysis remained stable. Mediation analysis showed the direct effect of the TyG index was -1.467 (-2.019, -0.948), with a total effect of -1.813 (-2.377, -1.286). The mediation effect of diastolic blood pressure (DBP), white blood cell count (WBC), and C-reactive protein (CRP) was -0.389 (-0.526, -0.268), -0.308 (-0.432, -0.177), and -0.252 (-0.453, -0.135), respectively. HGB was found to exert a suppressing effect on the relationship between the TyG index and VO₂max, with a value of 1.469 (1.252, 1.702). The p-values for all the above effects were <0.05.

In the US young and middle-aged population, the TyG index was significantly adversely associated with VO₂max levels. Females may exert an interaction on TyG. Evidence supported DBP, WBC, and CRP as intervening variables through which the TyG index exerts its influence on VO₂max. HGB may overrule the potential inverse association between the TyG index and VO₂max.NCHS IRB/ERB Protocol Number: Protocol #98-12.