Background: Nature's potentially positive effect on human health may serve as an important public health intervention. While several scientific studies have been performed on the subject, no systematic review of existing evidence has until date been established. Methods: This article is a systematic evaluation of available scientific evidence for nature-assisted therapy (NAT). With the design of a systematic review relevant data sources were scrutinised to retrieve studies meeting predefined inclusion criteria. The methodological quality of studies and abstracted data were assessed for intervention studies on NAT for a defined disease. The final inclusion of a study was decided by the authors together. Results: The included studies were heterogeneous for participant characteristics, intervention type, and methodological quality. Three meta-analyses, six studies of high evidence grade (four reporting significant improvement), and 29 studies of low to moderate evidence grade (26 reporting health improvements) were included. For the studies with high evidence grade, the results were generally positive, though somewhat ambiguous. Among the studies of moderate to low evidence grade, health improvements were reported in 26 cases out of 29. Conclusions: This review gives at hand that a rather small but reliable evidence base supports the effectiveness and appropriateness of NAT as a relevant resource for public health. Significant improvements were found for varied outcomes in diverse diagnoses, spanning from obesity to schizophrenia. Recommendations for specific areas of future research of the subject are provided.
