Nature-assisted therapy: systematic review of controlled and observational studies

Authors:
ANNERSTED Matilda, WAHRBORG Peter
Journal article citation:
Scandinavian Journal of Public Health, 39(4), June 2011, pp.371-388.
Publisher:
Informa Healthcare

A diverse range of nature-assisted therapies was reported in the thirty eight studies included. Although most studies found health improvements following intervention, the quality of the evidence was limited, with only six of the studies being randomised controlled trials. The strongest evidence was found for wilderness therapy. The outcome measures and the patient populations investigated also varied considerably. The difficulties associated with developing and evaluating complex interventions, such as nature-assisted therapy, are discussed.

Extended abstract:
Author

ANNERSTED Matilda; WAHRBORG Peter;

Nature-assisted therapy: systematic review of controlled and observational studies.

Journal citation/publication details

Scandinavian Journal of Public Health, 39(4), June 2011, pp.371-388.

Summary

A diverse range of nature-assisted therapies was reported in the thirty eight studies included. Although most studies found health improvements following intervention, the quality of the evidence was limited, with only six of the studies being randomised controlled trials. The strongest evidence was found for wilderness therapy. The outcome measures and the patient populations investigated also varied considerably. The difficulties associated with developing and evaluating complex interventions, such as nature-assisted therapy, are discussed.

Context

Although the beneficial effects of exposure to, and interaction with, natural environments – so called ‘natural treatments’ – are recognised, there is a lack of quantitative data from controlled studies and theoretical models on which to base the research. The aim of this study was ‘to systematically review the literature regarding effects of nature-assisted therapy, for patients with well-defined diseases, as a treatment option either alone, or together with other evidence-based treatment’.

Methods

What sources were searched?
Firstly, prior reviews were scrutinised for relevant articles. Electronic searches of the databases PubMed, Scopus, CSA Illumina, Agricola, Web of Science, Cochrane, CENTRAL, and Centre for Reviews and Disseminations were carried out and the website of the American Horticultural Therapy Association was searched. The reference lists of identified studies were then screened for further relevant material. The literature search was carried out between September 2008 and May 2009.

What search terms/strategies were used?
The terms for population type, nature-assisted intervention, and outcome used in the electronic searches are presented in Table 2. Individual searches are not specified.

What criteria were used to decide on which studies to include?
Intervention studies of nature-assisted therapy aimed at patients with an ICD 10 classified disease, or a well defined state of ill health, were included in the review. Studies had to be published in English between 1980 and May 2009. Eligible study designs were: systematic reviews or meta-analyses of randomised controlled trials, randomised controlled trials, non-randomised intervention studies, observational studies, or qualitative studies. Animal-assisted therapy studies were excluded.

Who decided on their relevance and quality?
Titles and abstracts were screened by the authors and the full-text of potentially eligible papers was obtained. Disagreements over whether an article should be included or not were resolved by discussion. Study quality was assessed by both authors using the GRADE system.

How many studies were included and where were they from?
Of the 6,485 articles obtained from the electronic search, 240 were potentially eligible for inclusion. The number of articles retrieved from each source and the reasons for exclusion are reported in Figure 1. Thirty-eight articles were included in the review; the geographical settings are not reported.

How were the study findings combined?
Data was extracted onto a standardised form. The review is narrative in nature; the results are grouped by study design in Table 3, and reported according to the different types of nature-assisted therapy, outcomes, and populations in the text. Outcome measures were classified as psychiatric, intellectual, sociological, or physical.

Findings of the review

There were three systematic reviews/meta-analyses, six randomised controlled trials, 12 non-randomised interventions, 14 observational studies, and four qualitative studies. The number of participants ranged from eight to 858. A diverse range of interventions were reported and included horticultural therapy, with or without other types of therapy, wilderness therapy, and unspecified nature-assisted therapy. Treatment comparisons also varied widely. The most commonly treated conditions were schizophrenia, dementia, depression, and substance abuse.

There was evidence that nature-assisted therapy had a significant effect within each of the four therapeutic areas examined and in a diverse range of patients. Four out of the six randomised controlled trials reported significant improvements in target outcomes; the three meta-analyses found modest effect sizes for wilderness therapy. Health improvements were found in 26 out of the 29 trials with less rigid study designs. Positive results tended to be reported immediately after treatment but not at follow-up.

Authors' conclusions

This review finds that a ‘small but reliable evidence base supports the effectiveness and appropriateness of NAT (nature-assisted therapy) as a relevant resource for public health. Significant improvements were found for varied outcomes in diverse diagnoses’.

Implications for policy or practice

None are discussed.

Related references

None
Subject terms:
ecotherapy, intervention, therapies, therapy and treatment, environment;
Content type:
systematic review
Link:
Journal home page
ISSN online:
1651-1905
ISSN print:
1403-4948

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