Effects of Physical Activity–Containing Interventions on Blood-Derived Biomarkers and Non-Invasive Cardiovascular and Vascular Outcomes in Early Childhood: A Systematic Review of Randomised Controlled Trials

Background/Objectives: Early childhood is an important period for the development of health-related behaviours and cardiometabolic risk trajectories. However, evidence regarding the effects of structured physical activity interventions on cardiometabolic and vascular outcomes in young children remains limited. This systematic review examined randomised controlled trials of physical activity–containing interventions in children aged 3–8 years that reported blood-derived metabolic or inflammatory biomarkers or non-invasive cardiovascular and vascular outcomes. Methods: Five databases were searched for randomised controlled trials published up to 2 October 2026. Eligible studies included children aged 3–8 years and evaluated interventions containing a structured physical activity component. Outcomes of interest included blood-derived metabolic or inflammatory biomarkers and non-invasive cardiovascular or vascular measures, such as blood pressure and pulse-wave velocity. Owing to substantial heterogeneity in intervention characteristics and outcome measures, findings were synthesised narratively. Results: The available evidence was limited and heterogeneous. Direct blood-derived biomarkers were assessed in two of the five included trials, both multicomponent programmes, whereas the remaining trials primarily evaluated blood pressure or arterial stiffness. Findings did not demonstrate a consistent intervention effect across cardiometabolic or vascular outcomes. The certainty of the evidence was low to very low. One exercise-only trial reported significant between-group improvements in selected blood-pressure outcomes, whereas another found no overall hemodynamic effect but reported favourable changes in an exploratory subgroup of children of mothers with a low educational level. The other trials reported no significant between-group effects on blood pressure or vascular measures. In the two trials assessing blood-derived biomarkers, no significant between-group differences were found. Conclusions: Current randomized evidence is insufficient to establish a consistent effect of physical activity–containing interventions on blood-derived biomarkers or non-invasive cardiovascular and vascular outcomes in early childhood. Evidence based on direct blood-derived biomarkers is particularly sparse. Larger trials with standardised outcome measures, prespecified biomarker panels, adequate assessment of intervention fidelity and longer follow-up are required.