Effects of forest bathing (shinrin-yoku) on serotonin in serum, depressive symptoms and subjective sleep quality in middle-aged males

Abstract

Background: We previously found that a forest bathing (shinrin-yoku) program significantly reduced the scores for depression, anxiety, anger, fatigue, and confusion and increased the score for vigor in the profile of mood states (POMS) test and showed a potential preventive effect on the depressive status in both males and females. In the present study, we investigated the effects of a forest bathing program on the level of serotonin in serum, depressive symptoms and subjective sleep quality in middle-aged males. Methods: Twenty healthy male subjects aged 57.3 « 8.4 years were selected after obtaining informed consent. These subjects took day trips to a forest park, the birthplace of forest bathing in Japan named Akasawa Shizen Kyuyourin, Agematsu, Nagano Prefecture (situated in central Japan), and to an urban area of Nagano Prefecture as a control in June 2019. On both trips, they walked 2.5 km for 2 hours each in the morning and afternoon on Saturday and Sunday, respectively. Blood was sampled in the afternoon before and after each trip. Concentrations of serotonin and lactic acid in serum were measured. The POMS test and a questionnaire for subjective sleep quality were conducted before and after the trips. Ambient temperature and humidity were monitoring during the trips. The Ethics Committees of the Nippon Medical School and Nagano Prefectural Kiso Hospital approved this study. Results: The forest bathing program significantly increased level of serotonin in serum, and significantly increased the score for vigor and decreased the score for fatigue in the POMS test. The forest bathing program also improved the sleepiness on rising and feeling refreshed (recovery from fatigue) in the Oguri-Shirakawa-Azumi sleep inventory MA version (OSA-MA). Conclusions: Taken together, the present study suggests that forest bathing may have potential preventive effects on depression (depressive status).

Effects of forest environment (Shinrin-yoku/Forest bathing) on health promotion and disease prevention —the Establishment of “Forest Medicine”—

“…Three studies investigated the effect of Shinrin-yoku on sleep [3,46,48,49]. We previously found that Shinrin-…”

“…In addition, forest bathing is particularly effective against mental stress (mental fatigue) [ 3 ]. Li et al [ 46 ] reported that Shinrin-yoku significantly increased level of serotonin in serum, and significantly increased the score for vigor and decreased the score for fatigue in the POMS test. Furuyashiki et al [ 47 ] conducted a comparative study of the physiological and psychological effects of a day-long session of Shinrin-yoku on working age people with and without depressive tendencies and demonstrated significant positive effects on mental health, especially in those with depressive tendencies.…”

“…Three studies investigated the effect of Shinrin-yoku on sleep [ 3 , 46 , 48 , 49 ]. We previously found that Shinrin-yoku significantly increased sleep time in middle-aged male office workers [ 3 ].…”

“…We previously found that Shinrin-yoku significantly increased sleep time in middle-aged male office workers [ 3 ]. Recently, my research team found that Shinrin-yoku significantly improved the sleepiness on rising and the feeling refreshed (recovery from fatigue) assessed by the Oguri-Shirakawa-Azumi sleep inventory MA version (OSA-MA), indicating that Shinrin-yoku may improve sleep quality [ 46 , 48 ]. Morita et al [ 49 ] also reported that two hours of forest walking improved nocturnal sleep conditions for individuals with sleep complaints, possibly as a result of exercise and emotional improvement.…”

“…It also has been reported that Shinrin-yoku effectively decreases blood glucose levels in type 2 DM (diabetes mellitus) patients and shows preventive effect on type 2 DM [ 60 ]. In addition, Shinrin-yoku shows potential preventive effects on depression by reducing stress hormones [ 8 , 9 , 21 , 29 , 31 , 32 , 36 ], by reducing negative emotions such as anxiety, depression, anger, fatigue, confusion, and by increasing the level of serotonin in serum and the positive feelings such as vigor [ 1 , 3 , 7 , 21 , 29 – 36 , 45 , 46 ]. Shinrin-yoku-induced increases of the level of serum adiponectin [ 29 , 36 ] and DHEA-S [ 29 ] also contribute to this effect.…”