Metabolic syndrome and cardiorespiratory fitness in children and adolescents: the role of obesity as a mediator

Objectives: To analyse the prevalence and association between metabolic syndrome (MetS), clustered cardiometabolic risk (CCMR), obesity (body mass index [BMI], fat mass [FM] and waist circumference [WC]), and cardiorespiratory fitness (CRF); and to assess whether obesity (BMI, FM, and WC) acts as a mediator between CRF and MetS or CCMR. Methods: This cross-sectional study included a subsample of the AFINA-te Study (n = 209; 11.51 +/- 0.72 years old). BMI, FM, and WC were assessed. The Course-Navette test was used to assess CRF. MetS was calculated following the International Diabetes Federation (IDF) definitions, and assessed using WC, triglycerides (TGs), high density lipoprotein (HD), fasting glucose (FG), and systolic and diastolic blood pressures (SBP/DBP). CCMR was calculated based on the sex and age-specific z score. Results: The prevalence of overweightness, obesity, MetS, and CCMR were 17.22, 1.44, 5.74, and 18.36%, respectively. After including BMI, FM, or WC into the model, the association between CRF and MetS was no longer significant, and the association between CRF and CCMR was only significant when it was mediated by BMI (beta = -0.006; p = 0.026). The rest of the analysis of the mediation did not show a direct effect, although a significant indirect effect with a significant value for the Sobel test was observed (all p < 0.001). Conclusions: BMI, FM, and WC act as full mediators in the association between CRF and MetS; FM and WC act as full mediators in the association between CRF and CCMR; and BMI acts as a partial mediator. The use of FM or WC as obesity variables is recommended.