Original ResearchEffect of forest bathing on physiological and psychological responses in young Japanese male subjects
Introduction
From the perspective that humans have adapted to the natural environment for millions of years, the current urban environment is an evolutionary new and unfamiliar habitat.1, 2 It has been shown that excess artificial environmental stimulation may have negative effects on human health,3 and that the urban physical environment can contribute significantly to individual and community health.4
In recent years, increasing attention has focused on the role of forests in promoting human health and well-being,5 including the field of medical research.6, 7, 8 Notable attempts have been made to incorporate forest environments into health promotion programmes.1, 9, 10, 11, 12 International research organizations, including the European Co-operation in the Field of Scientific and Technical Research and the International Union of Forest Research Organizations, have launched a new project entitled ‘Forests and Human Health’ to utilize the forest environment for human health. In some Asian countries such as China, Japan, Korea and Taiwan, forest bathing (taking in the forest atmosphere) is already popular and is considered a type of alternative therapy due to its health-promoting effects.13, 14, 15, 16, 17 However, despite the increasing interest and popularity of forest bathing, there is very little scientific evidence for its physiological effects.5, 18
Some theoretical foundation has been proposed. This includes the biophilia hypothesis,19 attention restoration theory20 and psycho-evolutionary theory,21 which support the hypothesis that a significant positive relationship exists between natural environments such as forests and human health.1 Ulich (1984)22 suggested a close relationship between landscape and recovery after surgery by demonstrating that patients with a view of vegetation recovered faster than patients with an artificial view. Greenery in living areas has positive effects on the perceived general health of residents,9 longevity in senior citizens23 and socio-economic health.24 Experimental studies have attempted to find more direct and specific effects of vegetation on mood6, 8 and emotional states,25 restoration from attentional fatigue20, 26, 27 and stress reduction.28, 29, 30 However, because few reliable scientific data have been obtained from field experiments,31 these studies have proven inconclusive. Other studies have been undertaken in controlled indoor settings.
A field study is urgently needed because this will provide a better indication of the effects in real environmental settings and increase the generalization of the effects, and will also have more direct social relevance than an indoor study.11 With recent developments in the technologies used for measuring human physiological functions, new approaches for field studies have been investigated to assess human physiological activity in outdoor settings. Recent field studies on forest bathing have provided interesting scientific data supporting the hypothesis that contact with forests has health benefits by quantifying various physiological indices, such as cerebral activity in the prefrontal area,32 heart rate variability (HRV),33, 34 pulse rate,31, 33, 34 blood pressure,31, 33, 34 salivary amylase activity,35 anticancer proteins,6, 7, 8 natural killer (NK) cell activity and number of NK cells,6, 7, 8 adrenaline and noradrenaline in urine,7, 8 and salivary cortisol concentration,31, 32, 33, 36 and psychological indices.6, 8, 17, 31, 32, 33, 34, 36 These studies have provided relatively clear results regarding the effects of forest environments on human physiological activities compared with artificial environments. However, the number of evidence-based studies is still insufficient to draw generalized conclusions. Also, there has been little research considering the possibility of phytoncides as one of the important factors associated with the physiological effects of forest environments.37
Therefore, this study examined the physiological benefits of forest bathing by investigating biological markers and the composition of phytoncides in real outdoor settings.
Section snippets
Participants
Twelve young Japanese male adults were recruited from local universities. At the recruitment stage, those who had past or current mental disorders, and those with cardiovascular or allergic diseases were screened. Those who were habituated to smoking or drinking were excluded. The adults who finally participated in the study had a mean age of 21.2 years [standard deviation (SD) 0.9] and a mean body mass index of 22.5 kg/m2 (SD 2.8). Before the experiment, the goal and protocol of the study were
Effect of forest bathing on parasympathetic and sympathetic nervous activity
The characteristics of real-time HRV in forest and urban sites are shown in Fig. 2. In the results of a 1-min HF power analysis, which reflects the activity of the parasympathetic nervous system, significantly higher values were obtained for forest stimuli than urban stimuli at 2–3 min (P < 0.05), 3–4 min (P < 0.01), 4–5 min (P < 0.05), 5–6 min (P < 0.05), 7–8 min (P < 0.05), 10–11 min (P < 0.05) and 11–12 min (P < 0.05) of the during stimuli period, and after 1–2 min (P < 0.05) for the after
Discussion
The data obtained in this study suggest that contact with forests has a positive effect on autonomic nervous system activity and reduces the level of salivary cortisol. HRV analysis indicated that the parasympathetic nervous system was activated and the sympathetic nervous system was suppressed when participants were in the forest, as indicated by the significantly higher HF power values and lower LF/HF ratio values in the forest compared with the urban site. The present result on the
Ethical approval
Ethics Committee of the Center for Environment, Health and Field Sciences, Chiba University.
Funding
Grants-in-Aid for Scientific Research (S; 16107007) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
Competing interests
None declared.
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