Changes in Urinary Hydrogen Peroxide and 8-Hydroxy-2′-Deoxyguanosine Levels after a Forest Walk: A Pilot Study

Abstract

Some studies have shown that exposure to forests has positive effects on human health, although the mechanisms underlying the health benefits of a forest environment have not been elucidated yet. The current study was aimed at examining how the levels of urinary hydrogen peroxide (H2O2) and 8-hydroxy-2’deoxyguanosine (8-OHdG) change after a forest or urban walk in healthy subjects. Twenty-eight volunteers (19 men and 9 women) participated in the study. The forest walks were carried out in a forest in Okayama Prefecture, Japan, and the urban walks (15 men and 7 women) were carried out in the downtown area of Okayama city, each for two hours. Spot urine samples were collected before the walk, the next day and one week after the forest or urban walk. Compared with pre-forest walk levels, urinary H2O2 (p < 0.1) and 8-OHdG (p < 0.1) concentrations significantly decreased in the participants the day after the forest walk; furthermore, urinary 8-OHdG remained at a low level even at one week after the forest walk (p < 0.05). However, there were no significant changes in the concentrations of these oxidative biomarkers after the urban walk. These findings suggest the possibility that exposure to forests may alleviate oxidative stress in the body.

Urinary 8-OHdG as a Biomarker for Oxidative Stress: A Systematic Literature Review and Meta-Analysis

“…A background range for 8-OHdG has been reported in different studies for healthy persons [11,[18][19][20]. However, these studies reported a wider range of values, making the identification of background cut-off values challenging.…”

Medical empirical research on forest bathing (Shinrin-yoku): a systematic review

“…Japanese scholars had the largest number of studies, publishing 13 papers [19, 20, 22–25, 28, 31, 38, 40, 42–44], accounting for 46% of the total number of included studies, followed by Chinese, South Korean, Taiwanese, and Polish scholars, publishing 6 papers [27, 32, 37, 39, 45, 46], 5 papers [21, 26, 29, 30, 34], 3 papers [33, 36, 41], and 1 paper [35], respectively, accounting for 21%, 18%, 11%, and 4% of the total number of included studies, respectively. Among them, there were 17 RCTs [20, 21, 24–27, 30–32, 35, 37–40, 43, 45, 46], accounting for 61% of the total number of included studies, and 11 NRCTs [19, 22, 23, 28, 29, 33, 34, 36, 41, 42, 44], accounting for 39% of the total number of included studies. The participants were dominated by healthy people, with a total of 17 studies [20, 24, 26, 29, 31, 33–38, 40, 42–46], accounting for 61% of the total number of studies included, and mostly young people aged 18–30.…”

Effects of a Forest Walk on Urinary Dityrosine and Hexanoyl-Lysine in Young People: A Pilot Study

“…The urban walks took place in July–October, 2016–2019 in the downtown area of Okayama City ( Figure 1 b), which has a population of 720,066 and a total area of 789.95 km 2 ; the general traffic amount is less than 30,000 cars and trucks/24 h). Each walk comprised 2 h of slow walking with a gait velocity of less than 60 m/min [ 17 ], during which there were two to three short breaks as described by Wang et al [ 8 ]. The urban walks were carried out in 2016–2019, and the forest walks in Shinjo Village were added to the study in 2017–2019 ( Table 1 ).…”

“…This imbalance may oxidatively damage DNA, proteins, and lipids [ 6 , 7 ]. Wang et al recently reported that urinary hydrogen peroxide (H 2 O 2 ) and 8-hydroxy-2′deoxyguanosine (8-OHdG) decreased after a forest walk but not after an urban walk [ 8 ]. Gibo et al also found a decreased serum malondialdehyde-modified low-density lipoprotein level (MDA-LDL) after a forest walk [ 9 ].…”

“…On the other hand, Im et al demonstrated that exposure to a forest environment for 2 h led to an elevation of serum antioxidant enzyme glutathione peroxidase [ 10 ]. This evidence probably suggests that exposure to a forest may play a role in alleviating oxidative stress and regulating the imbalance between the production and neutralization of ROS in the body [ 8 ]. However, more evidence is needed to support this potentiality.…”