1. Introduction
The term “forest bathing,” derived from Japan, is defined as being in a forest environment and absorbing its atmosphere in order to restore balance, both psychologically and physiologically [
1]. The literature on the subject has demonstrated the therapeutic effects of forest bathing on human health, including immune system improvement, cardiovascular disease prevention, and mental health enhancement [
2,
3,
4]. In 1983, Ulrich proposed a psycho-evolutionary theory, indicating the restorative effects of natural environments on stress [
5]. Moreover, the Attention Restoration Theory (ART) proposed by Kaplan and Kaplan also suggested the positive effects of natural environments on mental health [
6]. According to the ART, environments with four characteristics (i.e., being away, extent, fascination, compatibility) are beneficial to mental health. Compared to the urban environment, natural environments such as forests are more likely to have the abovementioned characteristics. Empirical studies have demonstrated that forest environments could improve mental health by enhancing positive emotions and reducing negative emotions. In one study, Tsunetsugu et al. [
7] compared subjects’ mood states in two different environments by adapting the Profile of Mood States (POMS). Their results show that subjects in forest environments had a lower level of negative emotions (e.g., tension–anxiety, confusion, fatigue, depression) and a higher level of vigor than those in urban environments, demonstrating the psychological benefits of forests in mental health. Similar results were reported by Takayama et al., who found that subjects’ tension-anxiety, depression-dejection, and confusion decreased after viewing forests [
8]. Other than POMS, some studies have assessed the change in anxiety by using the State-Trait Anxiety Inventory (STAI) [
9,
10]. Similar findings report that total scores of the STAI were significantly lower in the forest settings than in the urban settings, indicating the beneficial effects of forests in reducing anxiety [
4,
10].
The positive relationship between forest visits and physical health has been studied [
11,
12]. Tsunetsugu et al. [
13] found that subjects’ blood pressure and pulse rate were lower when immersed in the forests, compared to those in urban environments. Similar results were reported by Park et al. [
14], who analyzed 280 subjects in 24 experiment sites and observed lower pulse rates and blood pressure in the forest group, compared to the urban group. Regarding other physical indicators, Lee et al. [
15] found that subjects immersed in forest environments had higher high frequency power (HF) and lower low frequency power (LF) compared with those in urban environments; this result confirms the beneficial effects of forests in relaxation based on the evidence of higher parasympathetic activity. Park et al. and Lee et al. also observed higher HF in those immersing in forest environments [
16,
17]. Komori et al. [
18] used salivary α-amylase (SAA) to investigate the activity of the autonomic (sympathetic) nervous system. They found that SAA was significantly lower in forest environments than in urban environments, providing evidence for the restorative effect of forest environments. Similar results were reported by Yamaguchi et al. [
19]. They observed a decline in subjects’ SAA after sitting and taking in a view of the forest, although the results were not significant. In addition to their restorative effects, forests help prevent disease by improving immune function [
2,
20]. Li et al. [
20] observed an increase in the number of nature killer (NK) cells in subjects after a three-day (two-night) forest trip. Another study [
2] reports similar results: an increase in the number and activity of NK cells among female participants on a forest trip were observed despite the influence of estradiol and progesterone due to their menstrual cycles.
In Taiwan, it is estimated that about 60 percent of the landscape is covered by forest [
21]. Forest bathing is a popular forest recreational activity in China, Japan, Korea, and Taiwan, and is considered to be one approach to health promotion [
15]. Nonetheless, despite the increasing interest and popularity of forest bathing, evidence regarding the beneficial effects of forest bathing in Taiwan is limited [
12]. To this end, one of the purposes of this study was to provide scientific evidence by investigating the health effects of visiting forests in Taiwan. Additionally, unlike men, women have to deal with a physical transition once they have reached menopause. Symptoms of menopause include trouble focusing and sleeping, mood swings, weight gain, and more [
22]. Women who fail to manage menopause well not only increase their risk of having chronic conditions but also decrease their quality of life. Other than seeking medical treatments from doctors, visiting a forest may help enhance both of their psychological and physiological health. Yu and his colleagues found that forest camps contribute to the mental and physiological stability of postmenopausal women [
23]. As a result, the second purpose of this study was to explore the health improvement in middle-aged women after immersing in a forest environment. Accordingly, a two-day forest therapy program was designed and conducted in a National Forest Recreation Area in Taiwan. Middle-aged women’s psychological and physiological statuses were measured before and after the program to discern the health effects of the forest bathing trip. Findings of this study were expected to provide scientific evidence in terms of the effects of forest bathing on middle-aged women.
3. Results
Table 2 shows the results of paired sample t tests regarding the psychological differences before and after the forest therapy program. There was a significant decrease in four negative emotional states in the posttest, including confusion (
t = −3.514,
p < 0.01), fatigue (
t = −6.127,
p < 0.01), anger-hostility (
t = −3.656,
p < 0.01), and tension (
t = −2.162,
p < 0.05). In contrast, participants’ level of vigor increased significantly after the therapy program (
t = 5.014,
p < 0.01). Regarding anxiety, participants’ level had a significant decrease in the posttest (
t = −3.341,
p < 0.01).
Table 3 shows the results of paired sample
t tests, examining physiological differences between the pretest and the posttest. Compared with the pretest, there was a significant decline in systolic blood pressure in the posttest (
t = −2.533,
p < 0.05). Nonetheless, there was no significant difference regarding participants’ pulse rate, diastolic blood pressure, or SAA (all
p > 0.05).