CLINICAL AND ECONOMIC OUTCOMES OF NATURE-BASED HEALTHCARE INTERVENTIONS: SYSTEMATIC REVIEW PROTOCOL For Value Based Outdoor Healthcare

Chronic diseases represent the dominant driver of healthcare utilization and expenditure in the United States. Current estimates indicate that chronic conditions account for approximately 90% of the nation’s annual healthcare spending, reflecting the cumulative burden of cardio metabolic disease, mental health disorders, musculoskeletal conditions, and neurodegenerative illness (Centers for Disease Control and Prevention [CDC], 2022). Conventional treatment models for these conditions often rely heavily on pharmacologic management and episodic clinical care, approaches that have been increasingly challenged by rising costs, long-term medication dependence, and persistent gaps in patient-reported outcomes and functional health status. Within this context, healthcare systems are progressively transitioning toward value-based care models that prioritize improved patient outcomes relative to cost of care (Porter, 2010; Porter & Teisberg, 2006). Nature-based and outdoor healthcare interventions have emerged as a promising complementary approach to chronic disease management. These interventions encompass a diverse set of structured therapeutic activities conducted in natural environments, including forest bathing (shinrin-yoku), therapeutic hiking, green exercise programs, blue space exposure, wilderness therapy, and outdoor rehabilitation. An expanding body of interdisciplinary research spanning environmental health, behavioral medicine, rehabilitation science, and preventive cardiology suggests that exposure to natural environments may confer measurable physiological, psychological, and functional health benefits. Reported effects include reductions in stress biomarkers and depressive symptoms, improvements in cardiovascular and metabolic function, enhanced musculoskeletal mobility and rehabilitation outcomes, and potential neurocognitive benefits associated with cognitive restoration and neuroplasticity (Frumkin et al., 2017; Hansen et al., 2017; Kondo et al., 2018; Twohig-Bennett & Jones, 2018). Despite this growing evidence base, nature-based therapeutic approaches remain largely absent from contemporary value-based care frameworks and health system delivery models. One barrier to integration is the fragmentation of the existing literature. Research on outdoor and nature-based interventions is dispersed across multiple scientific domains, including environmental psychology, public health, physical activity research, and clinical rehabilitation. Interventions vary widely in design, duration, population, and outcome measurement, limiting the ability of healthcare systems and policymakers to evaluate their clinical effectiveness and economic value within standardized healthcare delivery structures. The emerging concept of Value-Based Outdoor Healthcare (VBOHC) proposes a clinical and research framework for integrating structured outdoor therapeutic interventions into healthcare systems using the principles of value-based care. Under this framework, outdoor healthcare interventions are evaluated according to their ability to produce measurable improvements in patient-centered outcomes while simultaneously reducing healthcare utilization and cost the dual criteria for value in healthcare delivery (Porter, 2010). However, to date, no systematic review has synthesized the existing evidence to evaluate whether nature-based healthcare interventions demonstrate such value across major chronic disease domains. The Oak Mountain Outdoor Healthcare Research Organization (OMOHC) has identified four priority clinical domains in which nature-based interventions may have significant therapeutic potential: mental health, cardio metabolic disease, musculoskeletal function, and early-stage neurodegeneration. These domains encompass several of the most prevalent and costly conditions within contemporary healthcare systems and represent key targets for preventive and rehabilitative interventions. A comprehensive synthesis of the existing literature is therefore necessary to evaluate the effectiveness of structured outdoor healthcare interventions across these domains. This systematic review will examine whether nature-based and outdoor healthcare interventions produce clinically meaningful improvements in health outcomes and whether these interventions demonstrate potential value within healthcare systems through reductions in healthcare utilization or cost. The results of this review will provide an evidence foundation for the development of standardized outcome measures and inform future consensus-building efforts, including Delphi-based expert evaluation of clinical outcomes within the Value-Based Outdoor Healthcare framework. 2. Review Question Specifically, this review will synthesize interdisciplinary evidence examining the effectiveness of outdoor healthcare interventions in adult populations with diagnosed conditions across four priority clinical domains identified by Oak Mountain Outdoor Healthcare (OMOHC): mental health disorders, cardio metabolic disease, musculoskeletal conditions, and early-stage neurodegenerative disease. These domains represent major contributors to chronic disease burden, healthcare utilization, and healthcare expenditure. Do structured nature-based or outdoor healthcare interventions improve clinical health outcomes compared with conventional care across the four OMOHC priority domains? Which types of outdoor healthcare interventions demonstrate the strongest evidence of therapeutic benefit? What physiological, psychological, or functional outcomes are most consistently associated with outdoor healthcare interventions? Do outdoor healthcare interventions reduce healthcare utilization, including hospitalizations, healthcare visits, or medication use? Do these interventions demonstrate cost savings or cost-effectiveness compared with conventional treatment approaches? What evidence exists regarding the economic value of outdoor healthcare interventions within healthcare systems or population health programs? Which intervention characteristics (e.g., duration, frequency, supervision level, environmental setting) are associated with improved health outcomes? Do intervention outcomes vary across patient populations, including differences in age, baseline disease severity, or comorbid conditions? What mechanisms of action are proposed in the literature to explain the health effects of nature-based interventions (e.g., stress reduction, increased physical activity, cognitive restoration)? Are certain clinical domains or conditions more responsive to outdoor healthcare interventions? What outcome measures are currently used to evaluate nature-based healthcare interventions? Which outcomes may be most appropriate for standardization within the Value-Based Outdoor Healthcare (VBOHC) outcomes framework?