Abstract Background: Current literature supports the compre…

Abstract
Background: Current literature supports the comprehensive health benefits of exposure to nature and green environments on human systems. The aim of this state-of-the-art review is to elucidate empirical research conducted on the physiological and psychological effects of Shinrin-Yoku (or Forest Bathing) in transcontinental Japan and China. Furthermore, we aim to encourage healthcare professionals to conduct longitudinal research in Western cultures regarding the clinically therapeutic effects of Shinrin-Yoku and, for healthcare providers/students to consider practicing Shinrin-Yoku to decrease undue stress and potential burnout. Methods: A thorough review was conducted to identify research published with an initial open date range and then narrowing the collection to include papers published from 2007 to 2017. Electronic databases (PubMed, PubMed Central, CINAHL, PsycINFO and Scopus) and snowball references were used to cull papers that evaluated the use of Shinrin-Yoku for various populations in diverse settings. Results: From the 127 papers initially culled using the Boolean phrases: “Shinrin-yoku” AND/OR “forest bathing” AND/OR “nature therapy”, 64 studies met the inclusion criteria and were included in this summary review and then divided into “physiological,” “psychological,” “sensory metrics” and “frameworks” sub-groups. Conclusions: 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.”.
Keywords: Shinrin-Yoku, forest bathing, nature therapy, integrative medicine
1. Introduction
Research conducted in transcontinental Japan and China points to a plethora of positive health benefits for the human physiological and psychological systems associated with the practice of Shinrin-Yoku (SY), also known as Forest Bathing FB (FB) [1,2,3]. SY is a traditional Japanese practice of immersing oneself in nature by mindfully using all five senses. During the 1980s, SY surfaced in Japan as a pivotal part of preventive health care and healing in Japanese medicine [4]. The reported research findings associated with the healing components of SY specifically hones in on the therapeutic effects on: (1) the immune system function (increase in natural killer cells/cancer prevention); (2) cardiovascular system (hypertension/coronary artery disease); (3) the respiratory system (allergies and respiratory disease); (4) depression and anxiety (mood disorders and stress); (5) mental relaxation (Attention Deficit/Hyperactivity Disorder) and; (6) human feelings of “awe” (increase in gratitude and selflessness) [5]. Moreover, various contemporary hypotheses, such as: Kaplan’s Attention Restorative Hypothesis [6]; Ulrich’s Stress Reduction Hypothesis [7]; and Kellert and Wilson’s Biophilia Hypothesis [8] provide support and a lens for the practice of SY and other forms of nature engagement.
Furthermore, SY may be considered a form of Nature Therapy (NT). Song, Ikei and Miyazaki’s present day model: Concept of Nature Therapy (CNT) [9] clearly defines NT as “a set of practices aimed at achieving ‘preventive medical effects’ through exposure to natural stimuli that render a state of physiological relaxation and boost the weakened immune functions to prevent diseases” [9]. The conceptual model of NT starts with a “stressed state” at the top and then points to the “restorative effects” of nature (forests, flowers, etc.) where there is a hypothesis of improvement in “physiological relaxation” and “immune function recovery” responses (individual differences noted). These responses to nature are then incorporated in the Evidence Based Medicine (EBM) model and is illustrated by an arrow leading to the “preventive medical effect.” This clear model supports Song, Ikei and Miyazaki’s [9] review of some medically proven outcomes. Kaplan and Kaplan [6] associated with exposure to naturally occurring stimuli (all 5 senses) that has a direct effect on increasing the parasympathetic nervous system and a heightened awareness that leads to a state of relaxation (Figure 1).
Individuals living and interacting in green spaces (GS) report being more energetic, in good overall health and, have more of a sense of meaningful purpose in life [10]. Current scientific findings are illuminating what humans intuitively know: nature has great benefits for the human brain and this is shown through increased happiness, health/well-being and cognition [5]. Historically speaking, Cyrus the Great intuitively built lush green gardens in the crowded urban capital of Persia 2500 years ago to increase human health and promote a sense of “calm” in a busy city. The 16th Century Swiss-German physi…