Rx: Walk in the Forest: Shinrin'Yoku's Holistic Healing Effects

Editor's Note: I confess to extreme bias on inviting this review from Margaret Mary Hansen, RN, MSN, EdD. I practice a sibling form of forest bathing: 3–4 days a week, year around, I stand-up paddle board on the Salish Sea (also known as the Puget Sound) that surrounds my home-office up the hill a few blocks from Seattle's Alki Point. While we paddle-boarders haven't the scientific literature on phytoncides and the other factors that confirm the value of nature in our lives, I offer the following N of 1 assertion. Between the salt air, sea-life visible on the sea floor of our inlet, sea-creatures rising up from below the surface and others, sea-linked, soaring above their prey, we find our similar restorative effects! I am pleased to have Dr. Hansen, a now retired Professor Emerita in Nursing and Health Professions at the University of San Francisco, to provide this brief commentary and narrative review of the research supporting forest bathing, or Shinrin'Yoku. In this small way, JACM helps Hansen, who continues research work in integrative medicine and nursing, to disseminate her call “to investigate what lies behind our nature loving neurons” and to position nature as an indispensable ally to be elevated in our own pursuit of health in individuals and communities. Powerful medicine! —John Weeks, Editor-in-Chief

The cost of healthcare in the United States has become exorbitant. ¹ The United States spent 17.8% of its gross domestic product on healthcare in 2016 and this cost reflects twice as much as other high-income countries, such as the United Kingdom, Canada, Germany, Australia, Japan, Sweden, France, Switzerland, Denmark, and the Netherlands. ¹ Moreover, in 2016, the United States demonstrated the poorest population health outcomes, the lowest life expectancy, as well as the lowest population older than 65 years. ¹ Complementary and alternative methods (CAMs) of healing, such as the Japanese practice of Shinrin'yoku (SY; 森林浴), literally translated as forest and bathing, are present in the literature for holistic health promotion; however, similar to other CAMs, it is not globally acknowledged and there is a call for more research. ^2,3

SY is the mindful practice of taking in the forest environment by actively allowing the five human senses to take in the beneficial effects of nature. ⁴ The recent U.S. National Public Health Week (April 1–7, 2018) inspired me to look at other countries, such as Japan, and to reach out to my Congressman and share with him the SY positive health outcomes reported in the literature. One burning question the author posed to the Congressman's assistant was: How might the tenets of SY be adopted by the U.S. government policy makers to support a national movement in creating a healthier nation? Based on the knowledge of SY's reported positive physiologic and psychologic effects on individuals, the author aims in this commentary to introduce a review of some empirical studies and models supporting the holistic effects of SY for healthcare and environmental researchers, government public health policy makers, and interested individual citizens. In addition, the author makes a call for qualitative research regarding the potential spiritual effects.

Twenty-first century contemporary individuals live in urban, industrial, and crowded spaces with stressed natural environments ultimately affecting the human psyche. In 2014, 54% of the global population lived in urban areas and a projected 66% will live in such areas by 2050. ⁵ Moreover, the global urbanized population is forecasted to be over six billion by 2045. Tokyo was ranked top in the United Nations' ⁴ report with 38 million people living in the city; however, central to the largest metropolis in the world is a large lush garden for its citizens to find respite. This increase in the global populace will result in an even more stressed environment and increased individual challenges associated with housing, transportation, energy, climate regulation, mental health, and employment. ⁵

Psychologically, researchers have conducted studies surrounding the amelioration of anxiety and overstressed human states by walking, sitting, hiking, or lying down in a forest and breathing in phytoncides (aromatic volatile compounds released by trees), such as the scent of cedar or hinoki cypress trees. ^{6 –8} Urban planning including increased green spaces, access to forests, and hiking/walking paths has empirically demonstrated human restorative effects, including relaxation and decreased mental and physical stress states. ⁹

Evidence-based medical practitioners may turn to Miyazaki's ³ Concept of Nature Therapy model (Fig. 1), illustrating an integrated preventative medical effect when consulting individuals.

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FIG. 1.

Concept of nature therapy. ¹² Permission to publish from Yoshifumi Miyazaki.

The conceptual model illustrates an individual in a stressed state. Exposure to the restorative effects of nature (flowers, forest, woods, and water) has a direct effect on individual physiologic and psychologic relaxation and then per the immune system there is recovery from the stressed state. These occurrences support evidence-based medicine and may be viewed as a preventative medical effect. Song, Ikei, and Miyazaki have conducted extensive research on the “preventative medical effect” while taking in to account individual differences. ^3,10

In addition, insomnia plagues many modern-day individuals; therefore, Morita et al. ¹¹ set out to study forest walking to increase relaxation and increase the number of hours of sleep. Ochiai et al. ¹² investigated the physiologic and psychologic effects of an SY program on adult females in the Akasawa Natural Recreational Forest in Japan. The findings determined that 17 middle-age females (average age of 62.2 ± 9.4 years) reported less negative mood states (p < 0.01) through the Profile of Mood States and an increase in vigor after the SY experience compared with the day before the SY experience. Significant decreases in pulse (p < 0.05) and salivary cortisol levels (p < 0.05) were determined, as well. These overall results point to a substantial health benefit for these middle-age females.

Significant research findings point to the positive effects of SY on well-known disease states, such as hypertension, cardiovascular disease, chronic-obstructive-pulmonary disease, diabetes mellitus type 2, cancer, and asthma. ² Mao et al. ¹³ determined participants' blood pressure readings and cardiovascular pathological factors were reduced by a decrease in the activation of the renin–angiotension cycle after a week-long exposure to a broad-leaved evergreen forest in China. Also, studies have focused on the volatile phytoncides produced by trees. ² Li et al. ¹⁴ used essential oils from the hinoki cypress tree through a humidifier on 12 healthy males residing in an urban hotel for three consecutive nights (13-h exposure each night). Findings indicated significant decrease in T cells, an increase in natural killer (NK) cell levels, and a significant decline in adrenaline and noradrenaline in participants' urine. Furthermore, physiologically, Kim et al. ¹⁵ determined that South Korean women (N = 11) diagnosed with stages I–III breast cancer benefited from SY by illustrating a significant increase in NK cell counts by 39% (p < 0.01).

Although scientists are not able to quantify the spiritual effects of SY, there is a curiosity on my part to conduct qualitative research to understand the lived experience of individual's spiritual feelings while being in nature. Historically, there is reference to the connection of nature and the human spirit. ¹⁶ Fisher's ¹⁷ Four Domain Model of Spiritual Health and Well-Being may serve as a paradigm because it includes the Personal, Communal, Environmental, and Transcendental aspects of human spirituality. The aforementioned Environmental aspect is noteworthy and may serve as a model for future SY qualitative research. Understanding the lived experience of individual's connections with nature on a spiritual level may also be supported by evolutionary biologist Wilson. ¹⁸ Wilson purports the human spirit is woven from our proclivity to be one with nature.