Nature-based interventions reduce physiological stress in children with chronic illnesses: evidence from salivary biomarkers

Introduction: Contact with nature is increasingly recognized as an important determinant of public health, yet limited objective evidence exists regarding its benefits for children with chronic illnesses. This study aimed to evaluate the short-term effects of a forest-based intervention on stress-related salivary biomarkers in vulnerable pediatric populations, including cancer survivors and children with neurodevelopmental disorders. Methods: A quasi-experimental design was used to assess 52 children aged 8–17 years, including both patients and their healthy siblings. Participants completed a 2.5-h guided immersion in a Mediterranean forest. Saliva samples were collected immediately before and after the intervention to measure cortisol, alpha-amylase, and immunoglobulin A levels. The study was approved by the Ethics Committee of the Hospital Clínico Universitario “Virgen de la Arrixaca” on June 29, 2021 (CEIC Code, 2021-6-10-HCUVA). Results: At the group level, significant reductions in cortisol and alpha-amylase were observed following the intervention, indicating acute stress relief. Subgroup analyses revealed notable decreases in cortisol and immunoglobulin A among children with neurodevelopmental disorders, while cancer survivors showed significant reductions in alpha-amylase. Discussion: This study provides novel biomarker-based evidence that brief exposure to natural environments can reduce physiological stress in children with chronic illnesses. These findings support the integration of accessible nature-based interventions into healthcare and community programmes to promote health, resilience, and overall wellbeing in pediatric populations.