Forest Bathing Enhances Human Natural Killer Activity and Expression of Anti-Cancer Proteins

Abstract

In order to explore the effect of forest bathing on human immune function, we investigated natural killer (NK) activity; the number of NK cells, and perforin, granzymes and granulysin-expression in peripheral blood lymphocytes (PBL) during a visit to forest fields. Twelve healthy male subjects, age 37-55 years, were selected with informed consent from three large companies in Tokyo, Japan. The subjects experienced a three-day/two-night trip in three different forest fields. On the first day, subjects walked for two hours in the afternoon in a forest field; and on the second day, they walked for two hours in the morning and afternoon, respectively, in two different forest fields. Blood was sampled on the second and third days, and NK activity; proportions of NK, T cells, granulysin, perforin, and granzymes A/B-expressing cells in PBL were measured. Similar measurements were made before the trip on a normal working day as the control. Almost all of the subjects (11/12) showed higher NK activity after the trip (about 50 percent increased) compared with before. There are significant differences both before and after the trip and between days 1 and 2 in NK activity. The forest bathing trip also significantly increased the numbers of NK, perforin, granulysin, and granzymes A/B-expressing cells. Taken together, these findings indicate that a forest bathing trip can increase NK activity, and that this effect at least partially mediated by increasing the number of NK cells and by the induction of intracellular anti-cancer proteins.

Trends in research related to “Shinrin-yoku” (taking in the forest atmosphere or forest bathing) in Japan

“…These researchers also found that the effect of the forest environments on the NK activity lasted for more than 7 days following the trip, whereas a corresponding trip to an urban area did not cause any changes in NK activity [45]. Based on their most recent study, they report that similar results of increased and lasting NK activity after ''Shinrin-yoku'' were confirmed in female subjects [46].…”

“…They first elucidated, by conducting an in vitro experiment, that essential oil(s) or odorous components of wood, such as cypress (hinoki) stem oil, a-pinene, and 1,8-cineole, significantly increased the NK activity, at least partially, via an increase in the intracellular levels of three cytolytic molecules, namely, perforin, granzyme A, and granulysin [43]. They subsequently conducted a field study with healthy male office-workers [44] and found that the NK activity of these office-workers significantly increased after they had experienced a 3-day/ 2-night stay in the forests. This enhancement in NK activity was at least partially mediated by an increase in the expression of the three cytolytic molecules mentioned above.…”

The physiological effects of Shinrin-yoku (taking in the forest atmosphere or forest bathing): evidence from field experiments in 24 forests across Japan

“…Further, cortisol concentration also holds great significance in terms of human immunological activity. Furthermore, the study of Li et al [34][35][36] reported that forest surroundings could aid in the recovery of the human immune system, as determined from the perspective of NK activity.…”

Two Weeks of Permanence in Negatively-Charged Air Conditions Causes Alteration of Natural Killer Cell Function

“…These repeated conditions may cause the steady stimulation of NK activity. Under similar circumstances, forest bathing trips are reported to enhance NK activity for approximately one month after people visit a forest area and stay for 3 days with a few hours of walking twice a day (41)(42)(43). The surrounding conditions of a forest, particularly near waterfalls, are thought to include plenty of negatively-charged particles.…”