Abstract
The purpose of this study was to evaluate the effect of a forest environment on salivary cortisol concentration, particularly on the characteristics of its distribution. The participants were 348 young male subjects. The experimental sites were 34 forests and 34 urban areas across Japan. The subjects viewed the landscape (forest or urban environment) for a period of 15 min while sitting in a chair. Saliva was sampled from the participants at the end of this 15-min period and then analyzed for cortisol concentration. Differences in the skewness and kurtosis of the distributions between the two environments were tested by performing a permutation test. The cortisol concentrations exhibited larger skewness (0.76) and kurtosis (3.23) in a forest environment than in an urban environment (skewness = 0.49; kurtosis = 2.47), and these differences were statistically significant. The cortisol distribution exhibited a more peaked and longer right-tailed curve in a forest environment than in an urban environment.
Highlights
There has been growing interest in the beneficial effects of the natural environment on human health
Mode was in the range from 5.73 to 6.55 nmol/L for both environments; the number of individuals with a higher cortisol concentration (>10 nmol/L) was larger in an urban environment (n = 84)
Cortisol concentrations were significantly lower in a forest environment than in an urban environment, and the permutation test revealed that these differences were statistically significant (p < 0.001)
Summary
There has been growing interest in the beneficial effects of the natural environment on human health. Positive responses to the natural environment have been demonstrated in various studies. Bowler [1] reviewed studies on the beneficial effects of natural environments and concluded that walking or running in natural environments reduced self-reported negative emotions such as anger, fatigue, and sadness. It has been shown that patients with exhaustion disorder perceived greater restorative and mood-enhancing effects as well as improved capacity for attention in forest environments compared to urban environments [2]. The effects of natural environments on affect, cognition, and physiology have been well established in laboratory and field experiments [3]. Rooftop green spaces may have beneficial effects, similar to those of outdoor natural environments, for elderly patients who require long-term care [4]. A large study observed lower mortality (especially due to cardiovascular diseases) in populations with greater exposure to green space, and this tendency was independent of income level [5]
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