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.
Highlights
Several researchers have reported that people who live in areas with more green space have fewer cardiometabolic diseases and a lower mortality risk, a decreased risk of poor mental health and cardiovascular diseases and a decreased risk of hyperlipidemia [1,2,3], the mechanisms underlying the health benefits of a forest environment have not been elucidated yet
Some reports from Japan demonstrated that a forest walk had positive effects on human physiological functions, such as a decrease in blood pressure among hypertensive patients [4,5,6] and an increase in human natural killer (NK) cell activity and anticancer protein expression [7]
Our results show that the 8-OHdG levels significantly decreased on the day after the forest walk but were still low one week later compared with the pre-forest walk levels, which differs from previous studies [8,14]
Summary
Several researchers have reported that people who live in areas with more green space have fewer cardiometabolic diseases and a lower mortality risk, a decreased risk of poor mental health and cardiovascular diseases and a decreased risk of hyperlipidemia [1,2,3], the mechanisms underlying the health benefits of a forest environment have not been elucidated yet.Some reports from Japan demonstrated that a forest walk had positive effects on human physiological functions, such as a decrease in blood pressure among hypertensive patients [4,5,6] and an increase in human natural killer (NK) cell activity and anticancer protein expression [7]. An early study found a decreased lipid peroxide level in the urine immediately after a forest walk [8]. Im et al showed that 2 h exposure to a forest environment increased the serum levels of glutathione peroxidase, an important antioxidant enzyme in the body [9]. When ROS generation exceeds the capacity of antioxidant defense systems in the body to remove them, this imbalance can cause oxidative damage to cellular constituents (DNA, proteins, lipids, etc.), which is defined as oxidative stress [10,11]. Few studies have examined the oxidative and antioxidative biomarkers in the body after exposure to a forest environment [8,9,14]
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