Mediation of obesity-related variables in the association between physical fitness and cardiometabolic risk in children and adolescents: A systematic review and meta-analysis

Objective To examine the mediation of obesity-related variables in the association between physical fitness and cardiometabolic risk in children and adolescents. Design Systematic review and meta-analysis. Data sources Studies from electronic databases from inception to 31 December 2023. Eligibility criteria for selecting studies Included were 123 observational studies (cross-sectional and longitudinal) that assessed risk by constructing a continuous score incorporating cardiometabolic parameters. Studies were considered if they evaluated at least one fitness component as an exposure in children and adolescents (5-19 years). Thirty-one were included in the main meta-analyses. Results Cross-sectional findings indicate that cardiorespiratory fitness is modestly but beneficially associated with cardiometabolic risk, either indirectly via obesity-related variables (indirect standardized beta coefficient [β Indirect ]=-0.17; 95% confidence interval [CI] -0.23; -0.11; inconsistency index [I 2 ]=94.4%) or directly and independently from obesity-related variables (r=-0.11; 95% CI -0.15; -0.07; I 2 =87.4%), whereas muscular fitness seems to be associated with risk only via obesity-related variables (β Indirect =-0.34; 95% CI -0.47; -0.20; I 2 =85.1%). There was no cross-sectional difference between biological sexes (p≥0.199). Longitudinal findings indicate no total (r=-0.12; 95% CI -0.24; 0.01; I 2 =23.1%) and direct (r=-0.03; 95% CI -0.08; 0.03; I 2 =0%) associations. Conclusion The association between fitness and risk appears to take place either indirectly through the reduction of obesity-related levels or directly by influencing risk. The latter underscores that the inverse association extends beyond a mere reduction in obesity-related variables, encompassing specific enhancements linked to exercise training, including increased metabolic efficiency, and cardiovascular capacity. PROSPERO registration number CRD42022354628.