Reviews - Meta-Analysis

Shinrin-Yoku (Forest Bathing) and Nature Therapy: A State-of-the-Art Review
In this metaanalysis from 2017,  127 papers that were using the phrases: “Shinrin-yoku” AND/OR “forest bathing” AND/OR “nature therapy” were analyzed. Out of those, 64 studies met the inclusion criteria and were considered for the summary review. They divide the benefits into “physiological,” “psychological,” “sensory metrics” and “frameworks” sub-groups. They found that human health benefits associated with the immersion in nature continue to be currently researched. Longitudinal research, conducted worldwide, is needed to produce new evidence of the relationships associated with Shinrin-Yoku and clinical therapeutic effects. Nature therapy as a health-promotion method and potential universal health model is implicated for the reduction of reported modern-day “stress-state” and “technostress.”.

Hansen MM, Jones R, Tocchini K. Shinrin-Yoku (Forest Bathing) and Nature Therapy: A State-of-the-Art Review. Int J Environ Res Public Health. 2017;14(8):851. doi: 10.3390/ijerph14080851. 

The Psychological and Physical Effects of Forests on Human Health: A Systematic Review of Systematic Reviews and Meta-Analyses
11 systematic reviews covering 131 different primary intervention studies, mostly from Asian countries, three of which included supplementary meta-analyses were reviewed. The quality assessment resulted in moderate confidence in the results of two reviews, low confidence in six, and critically low confidence in three.
The results of the eight moderate and low-rated reviews indicated that forest-based interventions are beneficial to the cardiovascular system, immune system, and mental health (in the areas of stress, depression, anxiety, and negative emotions). Evidence for the effectiveness of forest-based interventions on metabolic parameters in adults, the severity of atopic dermatitis in children and adolescents, and social skills and sociality in healthy primary school children was weak.

Stier-Jarmer M, Throner V, Kirschneck M, Immich G, Frisch D, Schuh A. The Psychological and Physical Effects of Forests on Human Health: A Systematic Review of Systematic Reviews and Meta-Analyses. Int J Environ Res Public Health. 2021;18(4):1770. doi: 10.3390/ijerph18041770.

Does Forest Therapy Have Physio-Psychological Benefits? A Systematic Review and Meta-Analysis of Randomized Controlled Trials
This study from 2022, comprised a systematic review and meta-analysis to determine how forest therapy affects the physiological and psychological health of adults.

The effect size was calculated by dividing blood pressure as a physiological indicator and depression as a psychological indicator.

Of the 16,980 retrieved studies, 17 were selected based on the inclusion criteria. Of these, eight

studies were included in the meta-analysis. The effect size of forest therapy on improving systolic

and diastolic blood pressure was not significant; however, it significantly reduced depression. While

the results have limited generalizability due to the inclusion of few studies, the effects of forest

therapy on reducing depression have been confirmed.

Yi Y, Seo E, An J. Does Forest Therapy Have Physio-Psychological Benefits? A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Int J Environ Res Public Health. 2022;19(17):10512. doi: 10.3390/ijerph191710512.

Effects of Forest-Based Interventions on Mental Health: A Meta-Analysis of Randomized Controlled Trials

This study from 2022 investigated the effects of forest therapy on anxiety, depression, and

negative and positive mental condition through a meta-analysis of recent randomized controlled

trials. Of 825 articles retrieved from databases, 6 met the inclusion criteria. The results of this study

showed that forest-based interventions improved the mental health of participants in the intervention

groups when compared to those in the control groups. Thirty-four outcome variables were analyzed

from six studies. The overall effect size of the forest therapy programs was 1.25 (95% CI = 0.93–1.57,

p < 0.001), which was large and statistically significant. These findings imply that forest-based

interventions can improve mental health as a nonpharmacological intervention.

Kang MJ, Kim HS, Kim JY. Effects of Forest-Based Interventions on Mental Health: A Meta-Analysis of Randomized Controlled Trials. Int J Environ Res Public Health. 2022 17;19(8):4884. doi: 10.3390/ijerph19084884.

Mapping of Research in the Field of Forest Therapy-Related Issues: A Bibliometric Analysis for 2007-2021

Based on 290 original articles, this study focuses on mapping the research in the field of Forest Therapy. The findings showed that the knowledge foundation of forest therapy was multidisciplinary with most published in the fields of environmental sciences and ecology but lacking input from social disciplines.

The research hotspots evolved from the early focus on individual benefits obtained from nature to increasing attention on human well-being at the social-ecological scale. More rigorous experiments with strict randomized controlled trials and blinding are needed to accommodate the trend of forest therapy toward non-pharmacological treatments.

According to Shneider’s four-stage theory, forest therapy research is in the third stage of the scientific research process. More future studies utilizing novel technologies and decision-making frameworks to solve practical issues are needed to introduce health into policies and promote human well-being.

 Wang X, Gong XF, Xiong KX, Guo DS, Liu LJ, Lin CM, Chang WY. Mapping of Research in the Field of Forest Therapy-Related Issues: A Bibliometric Analysis for 2007-2021. Front Psychol. 2022 Jul 11;13:930713. doi: 10.3389/fpsyg.2022.930713. PMID: 35898977; PMCID: PMC9309728.

Effects of forest bathing (shinrin-yoku) on levels of cortisol as a stress biomarker: a systematic review and meta-analysis.

This review aims to investigate the effects of forest bathing on levels of salivary or serum cortisol as a stress biomarker to understand whether forest bathing can reduce stress. 

A total of 971 articles were screened; 22 were included in the systematic review and 8 in the meta-analysis. In all but two included studies, cortisol levels were significantly lower after intervention in forest groups if compared with control/comparison groups, or a significant pre-post reduction of cortisol levels was reported in the forest groups. The main results of the meta-analysis showed that salivary cortisol levels were significantly lower in the forest groups compared with the urban groups both before and after intervention

Overall, forest bathing can significantly influence cortisol levels on the short term in such a way as to reduce stress, and anticipated placebo effects can play an important role in it. Further research is advised because of the limited available data.

Antonelli M, Barbieri G, Donelli D. Effects of forest bathing (shinrin-yoku) on levels of cortisol as a stress biomarker: a systematic review and meta-analysis. Int J Biometeorol. 2019;63(8):1117-1134. doi: 10.1007/s00484-019-01717-x. 

Effect of Forest Therapy on Depression and Anxiety: A Systematic Review and Meta-Analysis.

This systematic review and meta-analysis aimed to summarize the effects of forest therapy on depression and anxiety using data obtained from randomized controlled trials (RCTs) and quasi-

experimental studies. The findings showed that forest therapy is preventive management and

non-pharmacologic treatment to improve depression and anxiety. However, the included studies

lacked methodological rigor and required more comprehensive geographic application. Future

research needs to determine optimal forest characteristics and systematic activities that can maximize

the improvement of depression and anxiety.

Yeon PS, Jeon JY, Jung MS, Min GM, Kim GY, Han KM, Shin MJ, Jo SH, Kim JG, Shin WS. Effect of Forest Therapy on Depression and Anxiety: A Systematic Review and Meta-Analysis. Int J Environ Res Public Health. 2021;18(23):12685. doi: 10.3390/ijerph182312685.