A systematic review of randomized controlled trials on curative and health enhancement effects of forest therapy

Hiroharu Kamioka,¹ Kiichiro Tsutani,² Yoshiteru Mutoh,³ Takuya Honda,⁴ Nobuyoshi Shiozawa,⁵ Shinpei Okada,⁶ Sang-Jun Park,⁶ Jun Kitayuguchi,⁷ Masamitsu Kamada,⁸ Hiroyasu Okuizumi,⁹ Shuichi Handa<sup>9

1</sup>Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, ²Department of Drug Policy and Management, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, ³Todai Policy Alternatives Research Institute, The University of Tokyo, Tokyo, ⁴Japanese Society for the Promotion of Science, Tokyo, ⁵Food Labeling Division, Consumer Affairs Agency, Cabinet Office, Government of Japan, Tokyo, ⁶Physical Education and Medicine Research Foundation, Nagano, ⁷Physical Education and Medicine Research Center Unnan, Shimane, ⁸Department of Environmental and Preventive Medicine, Shimane University School of Medicine, Shimane, ⁹Mimaki Onsen (Spa) Clinic, Tomi City, Nagano, Japan

Objective: To summarize the evidence for curative and health enhancement effects through forest therapy and to assess the quality of studies based on a review of randomized controlled trials (RCTs).
Study design: A systematic review based on RCTs.
Methods: Studies were eligible if they were RCTs. Studies included one treatment group in which forest therapy was applied. The following databases – from 1990 to November 9, 2010 – were searched: MEDLINE via PubMed, CINAHL, Web of Science, and Ichushi-Web. All Cochrane databases and Campbell Systematic Reviews were also searched up to November 9, 2010.
Results: Two trials met all inclusion criteria. No specific diseases were evaluated, and both studies reported significant effectiveness in one or more outcomes for health enhancement. However, the results of evaluations with the CONSORT (Consolidated Standards of Reporting Trials) 2010 and CLEAR NPT (A Checklist to Evaluate a Report of a Nonpharmacological Trial) checklists generally showed a remarkable lack of description in the studies. Furthermore, there was a problem of heterogeneity, thus a meta-analysis was unable to be performed.
Conclusion: Because there was insufficient evidence on forest therapy due to poor methodological and reporting quality and heterogeneity of RCTs, it was not possible to offer any conclusions about the effects of this intervention. However, it was possible to identify problems with current RCTs of forest therapy, and to propose a strategy for strengthening study quality and stressing the importance of study feasibility and original check items based on characteristics of forest therapy as a future research agenda.

Keywords: forest therapy, randomized controlled trial, curative effect, health enhancement