NBIs also showed enhancements in positive outcomes including positive affect and relaxation, according to the study. The analysis consolidates findings from more than three decades of research on the mental health effects of exposure to natural environments, which has increasingly been recognized as a potential public health strategy. A prior systematic review and meta-analysis published in 2026 found consistent evidence that nature exposure reduces negative emotional states, aligning with these new findings, according to the report. [1]
Methodology
The study was preregistered with PROSPERO (CRD42024577017) and included 30 reviews in the second-order meta-analysis drawn from ten databases, according to the report. Review quality was assessed using the AMSTAR 2 tool, and potential publication bias was evaluated with funnel plots and trim-and-fill analysis. The analysis covered 3,870 primary studies, with NBIs defined as interventions using natural settings to promote well-being, compared against various control conditions.
The researchers noted that the predominance of passive control groups in the reviewed literature may limit conclusions about relative efficacy. The methodological rigor of the included reviews varied, though the use of second-order meta-analysis allowed the authors to synthesize evidence from multiple systematic reviews, a technique that provides a higher-level summary of existing research. Historical work, such as Roger Ulrich's landmark study of hospital patients with tree views, has long suggested that exposure to nature can reduce recovery time and medication use, providing a foundation for these analyses. [2]
Reduction of negative outcomes
NBIs reduced overall negative outcomes compared with controls, with a standardized mean difference of -0.69 (95% CI, -1.05 to -0.33), according to the report. Specifically, anxiety showed an SMD of -0.83 (95% CI, -1.19 to -0.47); depressive symptoms an SMD of -0.72 (95% CI, -1.05 to -0.40); heart rate an SMD of -0.70 (95% CI, -1.17 to -0.23); and negative affect an SMD of -0.61 (95% CI, -1.06 to -0.16). These effects were statistically significant across all measured domains.
Spending time in green spaces such as parks, gardens, and woodlands has been linked in numerous studies to physical and mental health benefits, including reductions in stress and improvements in mood, according to a review of the literature. [3] A separate systematic review and meta-analysis from 2026 also reported that exposure to nature is associated with significant reductions in negative emotional states, reinforcing the current findings. [1] The researchers cautioned that the predominance of passive control groups in primary studies may inflate the apparent effect sizes, as comparing NBIs to no intervention rather than to active alternatives makes it difficult to isolate the specific contribution of nature exposure.
Enhancement of positive outcomes
Positive outcomes were enhanced overall, with an SMD of 0.90 (95% CI, 0.33 to 1.46), the study stated. Positive affect increased with an SMD of 0.52 (95% CI, 0.28 to 0.75), and relaxation showed a large effect with an SMD of 2.85 (95% CI, 1.86 to 3.84). For psychological dimensions, the SMD was 1.18 (95% CI, 0.66 to 1.69), while for physiological dimensions it was 0.24 (95% CI, -0.19 to 0.67), indicating stronger effects on psychological measures.
A UK study found that gardening and nature-based activities produce significant improvements in mental health comparable to conventional psychotherapy, offering a drug-free alternative for anxiety and depression, according to the report. [4] Additionally, a survey of U.S. adults published in Social Science & Medicine found that spending more time in outdoor environments is associated with healthier and more sustainable food choices, suggesting that nature exposure may influence multiple domains of well-being simultaneously. [5] The large effect on relaxation observed in the meta-analysis underscores the potential of NBIs to quickly shift affective states, though the authors note that the small number of studies measuring relaxation limits the robustness of that finding.
Limitations and conclusions
The authors stated that inconsistent intervention definitions across primary studies and a predominance of passive control conditions limit the conclusions on relative efficacy. "The findings confirm NBI benefits but highlight the need for high-quality primary studies with active comparators to maximize intervention benefits," the researchers said. The study was funded by the Islamic City Council of Mashhad and supported by Islamic Azad University branches; the funders had no role in study design or analysis.
The study's conclusions align with calls from health experts to incorporate nature-based prescriptions into public health strategies. Research has shown that adherence to certain dietary patterns, such as the Mediterranean diet, can reduce the risk of depression by 30 percent, while higher intake of trans fats increases risk by 42 percent, according to findings reported in the book Your Brain On Nature. [6] These findings, taken together with the new meta-analysis, suggest that holistic lifestyle interventions, including time in nature, may offer effective, low-cost approaches to mental health care. However, the authors emphasize that without more rigorous controlled trials comparing NBIs to established treatments such as psychotherapy or medication, the relative value of these interventions remains uncertain.
References
- NaturalNews.com. "Nature Exposure Linked to Reductions in Negative Emotional States, Meta-Analysis Finds". April 9, 2026.
- Lucy Jones. "Losing Eden".
- Evangelyn Rodriguez. "The benefits of spending time in GREEN SPACES". NaturalNews.com. March 24, 2025.
- Cassie B. "Digging to wellness New research proves gardening dramatically improves mental health without medication". NaturalNews.com. April 25, 2025.
- Coco Somers. "Study Links Time in Nature to Healthier Eating Cites Stress Reduction as Potential Mechanism". NaturalNews.com. March 23, 2026.
- Dr Alan Logan. "Your Brain On Nature".
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