The escalating global prevalence of stress, anxiety, and depression has become one of the most pressing public health challenges of the 21st century. In response, researchers have been keen to identify effective interventions that can alleviate these widespread mental health issues. Among the emerging strategies, nature-based interventions (NBIs) have drawn significant attention for their potential to harness natural environments as therapeutic settings, aimed at promoting psychological well-being. However, despite a proliferation of studies and systematic reviews, there remains a striking lack of comprehensive synthesis combining these diverse findings into a cohesive understanding. Addressing this critical gap, a groundbreaking preregistered systematic overview and second-order meta-analysis has recently been published, shedding light on the aggregate effectiveness of NBIs across a remarkably wide dataset, composing millions of participant observations worldwide.
The study, spearheaded by Saeedy Robat and colleagues, represents an unprecedented endeavor to synthesize extant evidence by evaluating 116 systematic reviews in the overview, and distilling them further through a second-order meta-analysis of 30 reviews selected for methodological rigor. These reviews collectively encompass an astonishing 3,870 primary studies, reflecting data from over ten million estimated participants — an unparalleled scale that endows the conclusions with remarkable statistical power and generalizability. Notably, the scope of evaluation spans both psychological and physiological dimensions of health, thereby recognizing the complex interplay between mind and body in the context of stress, anxiety, and depression.
Central to the study is the observation that nature-based interventions demonstrably reduce overall negative outcomes related to these mental health disorders when compared with control groups. The standardized mean difference (SMD) for overall negative outcomes was found to be -0.69, with a 95% confidence interval (CI) ranging from -1.05 to -0.33, which signals a moderate to strong effect size. Parsing these results further reveals that NBIs significantly diminish symptoms of anxiety, with an SMD of -0.83, as well as depressive symptoms, which show an SMD of -0.72. Physiological markers such as heart rate also exhibited improvements, marked by an SMD of -0.70. The reduction in negative affect further corroborates the therapeutic potential of engagement with nature, which was quantified with an SMD of -0.61.
Crucially, the study not only highlights reductions in negative symptomatology but also underscores the ability of NBIs to foster positive psychological states. The positive outcomes across interventions were even more pronounced, with an overall SMD of 0.90. Within this domain, increases in positive affect (SMD 0.52) and relaxation (SMD 2.85) stand out as particularly compelling evidence of nature’s restorative properties. These findings are significant because they suggest that NBIs do more than simply reduce distress—they actively promote enhanced well-being. By elevating positive affective experiences and inducing pronounced states of relaxation, NBIs appear to facilitate pathways to resilience and improved mental health recovery.
Delineating psychological versus physiological positive outcomes was another noteworthy element of this meta-analysis. The psychological dimensions of well-being featured a large effect size (SMD 1.18), signifying robust improvements in mental states such as mood and perceived relaxation. On the other hand, physiological outcomes exhibited a more modest and statistically nonsignificant improvement (SMD 0.24). This dichotomy suggests that while the psychological benefits of exposure to natural settings are profound and consistent, physiological changes might be influenced by additional variables or require longer durations for measurable impact. This nuanced insight calls for deeper explorations into the mechanisms through which NBIs exert their effects and the temporal dynamics involved.
Despite these encouraging findings, the study authors sound a note of caution about limitations inherent in the primary research landscape. A large proportion of the reviewed studies utilized passive control groups, such as waitlists or no-treatment comparators, rather than active controls engaging participants in alternative interventions. This raises the possibility that some effects might partially reflect placebo or expectancy biases rather than specific properties of nature exposure. Moreover, the inconsistent definitions and operationalizations of what constitutes an NBI across studies complicate the synthesis of results and cloud interpretations regarding which types of interventions are most effective. These methodological shortcomings underscore an urgent need to standardize intervention protocols and deploy active comparator groups in future trials to rigorously assess relative efficacy.
Another salient aspect of this meta-analytic work is the stringent quality assessment implemented through AMSTAR 2, a validated tool for appraising systematic review quality. Such a layered approach to evaluation enhances confidence in the robustness of the conclusions, separating high-quality evidence from lower-quality or potentially biased research. This is essential in a field that is rapidly expanding yet remains vulnerable to publication bias and variable study rigor. Addressing publication bias was another methodological forte of this study, reinforcing that the observed positive effects are unlikely to be artifacts of selective reporting.
From a clinical and public health perspective, these findings herald important implications. NBIs could represent a scalable, low-cost, and accessible complement to traditional pharmacological and psychotherapeutic treatments, particularly relevant in nonclinical populations or as preventive strategies. The magnitude of effect sizes observed—especially for anxiety, depression, and positive affective states—rivals or even surpasses those reported for some established interventions, bolstering the case for integrating natural settings into mental health promotion frameworks.
Furthermore, the physiological benefits, albeit modest, open intriguing possibilities for holistic health interventions that simultaneously engage both body and mind. The observed heart rate reductions align with theories of autonomic nervous system regulation facilitated by nature exposure, suggesting pathways through which psychological distress might be alleviated via somatic mechanisms. Future research utilizing biomarkers and neuroimaging tools could richly deepen understanding of these biopsychological processes.
Importantly, the study acknowledges that NBIs are not one-size-fits-all solutions. Variation in intervention type, intensity, duration, and participant characteristics likely moderates outcomes and warrants personalized approaches. For example, passive viewing of natural scenes might differ in effect from active engagement in gardening or forest bathing, yet current evidence synthesis struggles to disaggregate these nuances. This points toward a future research agenda emphasizing mechanistic studies, intervention standardization, and the identification of moderators and mediators.
In summary, this comprehensive systematic overview and second-order meta-analysis crystallizes a compelling narrative: nature-based interventions hold substantial promise as both preventive and therapeutic tools against the escalating burdens of stress, anxiety, and depression. The convergent evidence gathered from millions of individuals worldwide affirms the salutary power of nature not only to diminish negative emotions and physiological arousal but also to foster profoundly positive psychological states and relaxation. However, real-world translation hinges on bolstering the evidence base through high-quality trials with rigorous controls and standardized methodologies.
As mental health systems grapple with increasing demand and resource constraints, NBIs emerge as an attractive adjunctive strategy grounded in evolutionary affinity with natural environments. These findings revitalise the call for urban planners, healthcare providers, and policymakers to rethink and reintegrate nature access as a fundamental component of public health infrastructure. Further interdisciplinary collaborations involving psychology, environmental science, and clinical medicine will be essential to realizing the full potential of nature for nurturing mental health resilience in an increasingly urbanized and technology-driven world.
Ultimately, this landmark synthesis not only consolidates prior fragmented research but amplifies an urgent message: embedded in nature lies a powerful remedy against the pervasive mental health crises of our time. Leveraging this potential mandates a concerted scientific commitment to refining, standardizing, and scaling nature-based interventions so that their benefits can be reliably harnessed, equitably distributed, and enduringly sustained.
Subject of Research: Nature-based interventions for stress, anxiety, and depression
Article Title: A systematic overview and second-order meta-analysis of nature-based interventions for stress, anxiety and depression
Article References:
Saeedy Robat, E., Bayazi, M.H., Nayyeri, M. et al. A systematic overview and second-order meta-analysis of nature-based interventions for stress, anxiety and depression. Nat Hum Behav (2026). https://doi.org/10.1038/s41562-026-02433-4
Image Credits: AI Generated
