A systematic overview and second-order meta-analysis of nature-based interventions for stress, anxiety and depression

The prevalence of stress, anxiety and depression is increasing globally. Nature-based interventions (NBIs), using natural settings to promote well-being, are recognized for their potential benefits, but synthesis is lacking. We conducted a preregistered (PROSPERO: CRD42024577017) systematic overview and second-order meta-analysis encompassing 116 systematic reviews in the overview and 30 reviews in the second-order meta-analysis from ten databases (representing 3,870 primary studies, over ten million estimated participants). The included systematic reviews evaluated NBI effects against diverse control conditions. Review quality was assessed (AMSTAR 2) alongside potential publication bias. NBIs were effective in reducing overall negative outcomes compared with controls (standardized mean difference (SMD), -0.69; 95% CI, -1.05 to -0.33), with significant reductions observed specifically for anxiety (SMD = -0.83; 95% CI, -1.19 to -0.47), depressive symptoms (SMD = -0.72; 95% CI, -1.05 to -0.40), heart rate (SMD = -0.70; 95% CI, -1.17 to -0.23) and negative affect (SMD = -0.61; 95% CI, -1.06 to -0.16). NBIs also enhanced positive outcomes (SMD = 0.90; 95% CI, 0.33 to 1.46), particularly positive affect (SMD = 0.52; 95% CI, 0.28 to 0.75) and relaxation (SMD = 2.85; 95% CI, 1.86 to 3.84). For positive outcomes, the SMD for psychological dimensions was 1.18 (95% CI, 0.66 to 1.69), while the SMD for physiological dimensions was 0.24 (95% CI, -0.19 to 0.67). The predominance of passive control groups and inconsistent intervention definitions across primary studies limit 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.