The Psychological Benefits of Forest Bathing in Individuals with Fibromyalgia and Chronic Fatigue Syndrome/ Myalgic Encephalomyelitis: A Pilot Study

doi:10.21203/rs.3.rs-3088899/v1

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The Psychological Benefits of Forest Bathing in Individuals with Fibromyalgia and Chronic Fatigue Syndrome/ Myalgic Encephalomyelitis: A Pilot Study

https://doi.org/10.21203/rs.3.rs-3088899/v1

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Background/Objectives.

The main objective of the present study is to assess the short-term effects of Forest Bathing (FB) conducted in a Mediterranean forest on individuals with fibromyalgia (FM) and/or Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) on perceived pain, fatigue, state anxiety, positive and negative affect, mood states, and state mindfulness. Methods.

A total of 44 participants with FM and/or CSF/ME agreed to participate in this study. The FB session consisted of a 3km silent walk, lasting three hours long and guided by a specialized psychologist and a mountain guide to guarantee the safety of the activity. Paired-sample t-tests were used to analyze the pre-post changes in perceived pain, fatigue, state anxiety, positive and negative affect, mood states and mindfulness.

Results.

All reported variables but self-reported pain showed statistically significant pre-post variations after the FB session. Particularly, large-to-very-large improvements in positive and negative affect, state anxiety, tension, depression, anger, and vigor were found. Small-to-moderate effect sizes for fatigue, friendliness and state mindfulness were also reported. Conclusions.

This study provides preliminary evidence of the short-term benefits of FB in individuals with FM and/or CFS/ME, especially on state anxiety and negative affect.

fibromyalgia

chronic fatigue syndrome

forest bathing

shinrin-yoku

forest therapy

mindfulness

In recent years, the role of forests in promoting and improving human health and well-being has been gaining scientific interest (Yi et al. 2022; Gobster et al. 2022; Piva et al. 2022; Shim et al. 2022; Qiu et al. 2022). In this regard, there are mounting studies supporting the beneficial effects of nature exposure in a broad range of health outcomes and populations across the globe with evidenced positive effects on life satisfaction, mental and general health, longevity, more regulated mood and emotional states, and cognitive processes (Herzog et al. 1997; Takano 2002; Maas 2006; Biedenweg et al. 2017; Kondo et al. 2018; Twohig-Bennett and Jones 2018; Bratman et al. 2019). It has also been reported that the effects of forest environment induce physiological relaxation with changes in stress hormones (i.e., cortisol) and the autonomic nervous system (Park et al. 2010; Lee et al. 2011, 2014; Tsunetsugu et al. 2013; Song et al. 2019). Benefits of nature exposure have also been demonstrated for even brief contemplative outdoor activities, such as forest walks and outdoor mindfulness practices, showing a positive effect on mental health in reducing, for instance, depressive and anxiety symptoms(Morita et al. 2007; Hansen et al. 2017; Oh et al. 2017; Muro et al. 2022).

Different theories exist regarding the association between nature and human health and well-being. For example, the Attention Restoration Theory proposes that spending time in nature can restore attention and prevent the mental fatigue associated with modern lifestyles (Kaplan 1995). Similarly, the Stress Reduction Theory hypothesizes that the connection with nature activates the parasympathetic nervous system and reduces autonomic arousal (Ulrich et al. 1991), which is related to stress. Similarly, the Biophilia hypothesis points out that humans naturally desire to interact with nature and all living things that belong to the natural world (Kellert and Wilson 1995). Finally, other explanations suggest that the benefits of nature rely on aspects that individuals encounter when they spend more time in nature, namely, an increase in levels of physical activity, a reduction in exposure to harmful environments (e.g., air pollution, noise, and artificial light), and an increase in exposure to sunlight and vitamin D(Stanhope et al. 2020; Jimenez et al. 2021; Yang et al. 2021).

Among nature connection practices is the Japanese practice of Shinrin-Yoku, also known as Forest Bathing (FB). FB may have remarkable psychological benefits associated with nature immersion, which could help manage and reduce the reported modern “stress-state” (Hansen et al. 2017; Timko Olson et al. 2020). The FB practice consists of mindful walking in a natural setting, quietly aimed at promoting communication and contact with nature, and it is usually carried out by specialized guides (Hansen et al. 2017). FB is a form of “Nature Therapy”, defined by Song, Ikei and Miyazaki (2014; 2016) as “a set of practices aimed at achieving ‘preventive medical effects’ through exposure to natural stimuli that render a state of physiological relaxation and boost the weakened immune functions to prevent diseases”.

Evidence suggests that FB has psychological and overall health benefits. A recent review indicates that FB may increase natural human killer cell activity, reduce blood pressure and heart rate, diminish stress hormones, balance the autonomic nervous system, improve sleep, reduce anxiety, depression, anger, fatigue, and confusion, and increase vigor (Li 2022). However, the majority of the studies in FB are performed in Asian countries, with small sample sizes, with an over-representation of young and healthy men, needing more evidence to confirm the therapeutic effects of forests on health in other countries around the world and, particularly, in heterogeneous clinical populations (Lee et al. 2011; Song et al. 2019; Muro et al. 2022).

FM is a highly prevalent rheumatic syndrome (2–8% of the general population), usually diagnosed between 20 and 50 years old (Häuser et al. 2015). It is characterized by chronic, diffuse musculoskeletal pain, fatigue, sleep disorders, high levels of distress and comorbidity with anxiety and depressive disorders (Clauw 2014). FM has recently been considered a functional somatic disorder, evolving from a primary pain disorder with a neurobiological basis to a broader biopsychosocial disorder (Wolfe and Rasker 2021). Although there is no curative treatment for this disease, pain education, cognitive behavioral therapy and therapeutic exercise are considered adequate approaches to manage FM symptoms, with an evidence level of 1A(Malfliet et al. 2019).

FM is usually comorbid with other central sensitization syndromes such as CFS/ME(Kato et al. 2006; Yunus 2007; Castro-Marrero et al. 2017) in over 50% of the cases(Faro et al. 2014). CFS/ME is a disabling and complex illness that affects approximately 1% of the population (Lim et al. 2020)and is characterized by persistent post-exertional fatigue and substantial symptoms related to cognitive, immune and autonomic dysfunction, including sore throat, muscle pain, joint pain, weakness, sleep disturbance, memory loss, and poor concentration (Brurberg et al. 2014; Cortes Rivera et al. 2019). This medical condition negatively impacts individuals’ quality of life, including their psychological, emotional and social well-being (NICE 2021).

FB seems to be a promising intervention for promoting better mental health and well-being; however, there is a scarcity of studies exploring its effects in clinical samples; mainly, as far as we know, only one study uses FB in patients with FM. In this pilot study conducted in Spain by López-Pousa et al. (2015), 30 individuals with FM were included and randomly allocated to a group of aerobic exercise-based program (i.e., 1.25-kilometre walks during six days in a time-frame of 2 weeks) in a mature (n = 15) or in a young forest (n = 15). Although both groups showed decreases in FM symptoms, the group that performed the walk in the mature forest showed greater improvements in terms of r in days with intense pain, insomnia and more days of well-being. Regarding the effects of nature exposure in individuals with CFS/ME, in a recent study including 24 participants with CFS/ME, who were randomly allocated to outdoor daily living activities (for 6 days, at least 3 hours each) in a waterfall forest environment or to activities in an urban context, noticed that this natural context compared to urban areas improved their psychological state and enhanced immunity (Zhu et al. 2021).

The main objective of the present study is to assess changes in self-reported pain, fatigue, mental health and psychological well-being indicators after a 3-hour FB session conducted in a Mediterranean forest in a sample of individuals diagnosed with FM and/or CFS/ME. We hypothesize that compared to baseline, after the FB session, participants will report lower levels of state anxiety, negative affect, anger, fatigue, tension, depressive mood, perceived pain, and perceived fatigue and higher levels of positive affect, vigor, friendship, and state mindfulness.

Design

A pre-post study design was used with self-report assessment at baseline and after a 3-hour FB session.

Procedure

All participants were recruited using social media posting (mainly through an inclusive hiking club association called CIM project -Associació Esportiva Projecte Inclusiu CIM-). The activity was free to all individuals with FM and CFS/ME and participation of their families was also encouraged. The FB session was carried out in the Barcelona surrounding area, on the 10th of October 2021, at 10h a.m. The route started at 41°25'12.3"N 2°05'49.2"E coordinates. This area corresponds to the “Baixador de Vallvidrera'' train station, which is very well-connected with Barcelona center (approx. 15 minutes by train). “Baixador de Vallvidrera '' is part of the Serra de Collserola, a mountain range of more than 8,000 hectares, that is part of the Catalan Coastal Range and located between the rivers Besòs and Llobregat. The vegetation in Collserola is predominantly Mediterranean, consisting of a mix of evergreen and deciduous tree species. It contains many Mediterranean natural environments, especially forests, although low vegetation formations (maquis) also abound. Over a thousand major plants and around thirty plant communities have been catalogued, including forests of aleppo pines and nut pines, evergreen oaklands, riverside copses, maquis and scrublands, brush, and savannah grasslands. The original forest is the coastal holm oak grove (holm oak tree layer with a second shrub layer of common laurustine); however, due to human action (e.g., fires, grassland), most of the mountain range is also covered by aleppo pines. The forest also features dense undergrowth with various herbaceous plants, including wildflowers, grasses, and ferns. In addition to its natural features, the Collserola forest also serves as a recreational area for outdoor activities such as hiking, mountain biking, and nature observation.

A masked unipersonal code was given to each participant, and then a link to an online questionnaire was sent by email. Participants answered the baseline questionnaire approximately 1h before starting the FB and in the first 24 hours after the FB session.

Description of the FB Session

The session was guided by one specialized psychologist with expertise in FB (A.M.), a specialized psychologist and physiotherapist in fibromyalgia (M.S.), and three mountain guides to guarantee the safety of the activity. The FB activity consisted of a 3km silence walk in 3 hours, with the realization of three 10-minute stops (i.e., before starting the walk, in the middle and at the e it) with practices of deep breathing and mindful awareness of the five senses in nature. A similar FB protocol was used in the study by Muro et al. (2022).

Sample

A total of 44 participants with FM and/or CSF/ME agreed to participate in this study. The inclusion/exclusion criteria were: to be diagnosed with FM, SFC/ME, or both syndromes by a rheumatologist, to have more than 18 years of age, to be able to understand Spanish and to be able to provide written informed consent.

All participants consented to collaborate voluntarily and provided informed consent before participating in the study. The ethics committee of the Autonomous University of Barcelona approved the study in advance (reference code UAB5339).

Instruments

The survey was designed to gather data about the following:

Sociodemographic and clinical characteristics

age, body mass index (BMI), educational level, site of residence (urban or rural), illness self-perceived start (ISPS), and incapacity certificate. Furthermore, physical exercise habits (i.e., weekly amount of practice, exercise intensity and type of physical exercise) were also recorded.

The Depression Anxiety Stress Scales-21 (DASS-21; Lovibond and Lovibond 1995) was administered to assess depressive, anxiety and stress symptoms of the sample at baseline. The DASS-21 is a 21-item self-reported scale that assesses symptoms of depression, anxiety and stress (7 items each) in non-clinical and clinical, including chronic pain, samples (Taylor et al. 2005). Each item is scored from 0 (did not apply to me at all over the last week) to 3 (applied to me very much or most of the time over the past week) and asks for symptoms presented over the previous week. Total scores in each subscale may range from 0 to 21, with higher scores indicating a more severe status. The Spanish adaptation of the DASS-21 has an adequate internal consistency (with Cronbach’s alphas of 0.84, 0.70, and 0.82 for depression, anxiety and stress, respectively (Bados et al. 2005).

The 20-item subscale for assessing state anxiety levels (“right now”) from the State-Trait Anxiety Inventory- State (STAI; Spielberger 1972; Riquelme and Buela-Casal 2011) was used. It is a 4-point Likert scale ranging from 1 (not at all) to 4 (very much so). High scores correspond to altered states related to anxiety; low scores suggest an absence of stress and emotional stability. The Spanish version of the STAI state showed an internal consistency of Cronbach’s α = 0.94 (Riquelme and Buela-Casal 2011).

The Positive Affect and Negative Affect Scale (PANAS; Watson and Tellegen 1985; López-Gómez et al. 2015) was used. It consists of two subscales of 10 items each for assessing positive and negative affect using a 5-point scale from 1 (very slightly or not at all) to 5 (extremely). Scores of each subscale can range from 10–50, with higher scores meaning higher positive and negative affect levels. The scale has shown good psychometric properties in Spanish samples (Díaz-García et al. 2020) with internal consistency indexes (Cronbach’s alpha) of 0.92 for the Positive Affect Scale and 0.88 for Negative Affect Scale.

The State Mindfulness Scale (SMS; Tanay and Bernstein 2013) consists of 21 items with a 5-point response scale that ranges from 1 (not at all) to 5 (very well) to evaluate the degree of conformity with the proposed assertions related to their experiences in the last 15 minutes. It is focused on two dimensions: mindfulness state of mind (related to thoughts) and mindfulness state of body (related to physical sensations). Higher scores represent a higher level of state mindfulness. In this study sample, this test showed an optimal internal consistency of Cronbach’s α = 0.97, consistent with data obtained by Tanay and Bernstein (Tanay and Bernstein 2013), who reported internal solid consistency reliabilities (α = .90–.95).

The Profile of Mood States (POMS; McNair et al. 1971; Andrade et al. 2010) consists of 30 items measuring six mood states (anger, fatigue, vigor, friendship, tension, and depressive symptoms). Participants are requested to rate each item using a 5-point Likert Scale from 0 (not at all) to 4 (extremely). Higher scores indicated higher levels of that mood state. POMS subscales of the Spanish validation showed Cronbach’s αs between 0.78 (friendship) and 0.87 (fatigue).

A Visual Analog Scale for rating pain intensity in the present moment (VAS PAIN; Hayes and Patterson 1921), with extremes from 0 (no pain) to 10 (unbearable pain), was used. Similarly, a VAS for assessing fatigue (VAS FATIGUE; Hayes and Patterson 1921) with extremes from 0 (i.e., lots of energy) to 10 (i.e., no energy) was used.

Statistical Analyses

Descriptive statistics such as means (with standard deviations) and frequencies were calculated for the sociodemographic and clinical characteristics. Paired-sample t-tests were used to analyze the pre-post changes in outcome measures before and after the FB. For a more precise interpretation of the relevance of the results in each assessed domain, effect sizes for pre-post changes were also calculated using Cohen’s d (rule of thumb for Cohen’s d: 0.2 = small, 0.5 = medium, and 0.8 = large effect sizes). All the statistical analyses were made using the SPSS 21.0 program, assuming a statistical significance level of 5%.

Most of the participants were diagnosed with both FM and CFS/ME (n = 37, 80.4%). Three participants had only an FM diagnosis (6.5%), and five had only a CFS/ME diagnosis (10.9%). All participants were women, with a mean age of 54 years, ranging from 26 to 69, with a BMI of 28.31 ± 6.46. Most (93.2%) lived in urban areas and achieved secondary or higher education (61.4%). They had an average of 11–13 years of self-perceived illness start/duration (in years) and showed moderate-to-high levels of pain (scoring 6–7 out of 10) and fatigue (scoring 7–8 out of 10). More than half (56.8%) had a recognized disability degree of 33% or more. According to the DASS-21 standard cut-offs (Lovibond and Lovibond 1995), 47.7% of the sample rated severe or highly severe for Depression, 53.5% for Anxiety, and 31.8% for Stress. In addition, participants reported that they were not very physically active individuals, as 84.1% of the participants used to practice light exercise (such as walking) twice a week (see Table 1).

Table 1

Sociodemographic and Clinical Characteristics of the Study Sample
	Total sample (n = 44)
Sociodemographics
Age (years), M ± SD	53.82 ± 8.57
Women, n (%)	44 (100)
Only fibromyalgia	3 (6.80)
Only CFS/ME	4 (9.10)
Fibromyalgia and CFS/ME diagnosis	36 (81.80)
BMI, M ± SD	28.31 ± 6.45
Educational level, n (%)
Primary Education	13 (29.50)
Secondary Education	16 (36.40)
Higher Education	11 (25.00)
Other	4 (9.10)
Residence, n (%)
Urban area	41 (93,20)
Rural area	3 (6.80)
Clinical characteristics
VAS Pain, M ± SD	6.64 ± 1.88
VAS Fatigue, M ± SD	7.48 ± 1.42
Fibromyalgia ISPS (years), M ± SD	13.49 ± 10.89
CFS/ME ISPS (years), M ± SD	10.93 ± 10.01
Incapacity certificate, n (%)
No	12 (27.30)
Requested	7 (15.90)
Between 33% and 66%	21 (47.70)
More than 66%	4 (9.10)
DASS Depression, n (%)*
Normal 0–9	15 (34.10)
Mild 10–13	4 (9.10)
Moderate 14–20	4 (9.10)
Severe 21–27	7 (15.90)
Extremely severe + 28	14 (31.80)
DASS Anxiety, n (%)*
Normal 0–9	12 (27.30)
Mild 10–13	2 (4.50)
Moderate 14–20	6 (13.60)
Severe 21–27	7 (15.90)
Extremely severe + 28	17 (38.60)
DASS Stress, n (%)
Normal 0–9	14 (31.80)
Mild 10–13	7 (15.90)
Moderate 14–20	9 (20.50)
Severe 21–27	8 (18.20)
Extremely severe > 28	6 (13.60)
Physical exercise habits
The weekly amount of physical exercise, n (%)
< 1 hour per week	10 (22.70)
1–2 hours per week	13 (29.50)
2–3 hours per week	10 (22.70)
> 3 hours per week	8 (18.20)
No exercise	3 (6.80)
The intensity of weekly exercise sessions, n (%)
Very light	14 (31.80)
Mild	18 (40.90)
Moderate	8 (18.20)
Physical exercise type, n (%)
Walking	37 (84.10)
Yoga	1 (2.30)
Nordic Walking	1 (2.30)
Other	3 (6.80)
Note: *Levels according to DASS-21 standard cut-offs (Lovinbond & Lovibond, 1995).

Most psychological indicators showed statistically significant pre-post variations after the intervention (see Table 2). More precisely, there was a statistically significant decrease in negative affect (p < 0.001; d = 0.84), state anxiety (p < 0.001; d = 1.31), anger (p < 0.001; d = 0.84), fatigue (p = 0.009; d = 0.40), tension (p < 0.001; d = 1.05), and depression (p < 0.001; d = 1.21). Moreover, a significant increase in positive affect (p < 0.001; d = 0.85), vigor (p < 0.001; d = 0.84), friendship (p = 0.001; d = 0.44), mindfulness of body (p < 0.001; d = 0.48) and mindfulness of mind (p < 0.001; d = 0.64) was noted. There was also a significant decrease in fatigue levels (p = 0.003; d = 0.46) after the FB. There were no significant differences in pain intensity (p = 0.421; d = 0.14).

Table 2

Observed Changes after Forest-Bathing Practice.
	M (SD) Pre (n = 44)	M (SD) Post (n = 42)	Pre-post diff. M (SD)	95% CI	t	p	d
VAS Pain	6.64 (1.88)	6.31 (2.62)	0.33 (2.63)	− .48, 1.13	0.813	0.421	0.14
VAS Fatigue	7.48 (1.42)	6.36 (2.76)	1.12 (2.31)	.41, 1.83	3.167	0.003	0.46
PANAS Positive affect	25.52 (8.91)	34.07 (9.56)	-7.98 (6.72)	-10.05, -5.91	-7.779	< 0.001	0.85
PANAS Negative affect	22.84 (10.00)	14.80 (6.73)	7.49 (8.60)	4.84, 10.13	5.713	< 0.001	0.84
STAI Anxiety state	31.59 (14.54)	13.47 (11.71)	17.63 (12.62)	13.74, 21.51	9.162	< 0.001	1.31
POMS Anger	5.11 (5.40)	1.23 (2.78)	4.09 (5.34)	2.45, 5.74	5.022	< 0.001	0.84
POMS Fatigue	12.18 (5.21)	9.85 (6.07)	2.35 (5.62)	.62, 4.08	2.739	< 0.01	0.40
POMS Vigour	6.36 (4.57)	10.69 (4.97)	-4.09 (4.33)	-5.43, -2.76	-6.198	< 0.001	0.84
POMS Friendliness	14.54 (4.52)	16.69 (3.78)	-1.93 (3.55)	-3.02, − .84	-3.567	0.001	0.44
POMS Tension	9.29 (6.70)	2.71 (4.00)	6.35 (5.33)	4.71, 7.99	7.816	< 0.001	1.05
POMS Depression	9.63 (6.30)	2.80 (3.76)	6.53 (6.34)	4.58, 8.49	6.762	< 0.001	1.21
SMS Mindf. body	23.22 (5.38)	25.80 (4.37)	-2.40 (4.11)	-3.66, -1.13	-3.820	< 0.001	0.48
SMS Mindf. mind	55.13 (13.09)	63.42 (11.35)	-8.02 (9.12)	-10.83, -5.22	-5.766	< 0.001	0.64

The main aim of this study was to assess if a FB session could improve several outcomes in individuals with FM and/or SFC, with a particular focus on mental health and well-being. These results are strengthened given the notable clinical severity of the individuals included, with moderate-to-high reported levels of pain and fatigue (cardinal symptoms of FM and CFS/ME), a high rate of recognized disability degree and high depressive and anxious symptomatology. Furthermore, regarding the generalizability of the findings, more than 80% of the participants reported only performing light exercise (such as walking) twice a week, so we can ascertain that they are not only very physically active (a behavioral pattern not usually seen in these conditions) individuals were enrolled in this study.

Overall, the results obtained in this pilot study align with previous studies in Asian and Mediterranean forests and show how FB may help in fostering mental well-being (Hansen et al. 2017; Wen et al. 2019; Timko Olson et al. 2020; Muro et al. 2022, 2023). The current study found a decrease in negative affect, state anxiety, anger, fatigue, tension, and depression and an increase in positive affect, vigor, friendship, and mindfulness state in a clinical sample of individuals showing FM and/or SFC/ME. However, contrary to expectations, this study did not find a significant improvement in self-reported pain following the FB session. This study's results also align with previous studies that reported increased well-being after contact with nature, especially following a FB session (Antonelli et al. 2019; Yang et al. 2021; Gobster et al. 2022; Shim et al. 2022). As these studies suggest, FB might produce its benefits because it would increase exposure to nature, which is related to normalizing the stress-response system. In addition, our results also indicated an increase in state mindfulness, consistent with the Attention Restoration Theory (Kaplan 1995). According to this theory, spending time in nature has health benefits since it decreases attentional fatigue caused by the modern lifestyle. Therefore, the mindful state generated by the FB practice might have enabled individuals to enjoy the present moment and focus on the environment, the exercise or the silent company of other people instead of on their distressing internal states or engaging in ruminating tendencies. Furthermore, our results showed increased friendliness following the FB practice, previously documented in some studies (Jimenez et al. 2021; Muro et al. 2022; McEwan et al. 2022). In other words, FB may provide a shared experience with a space for socialization in which new bonds and connections may be created, which might increase social support. These findings highlight the potential of FB as a holistic intervention that promotes physical and mental health through exposure to nature and fosters mindfulness and social connection, contributing to overall well-being.

It is important to note that most of the studies mentioned above have been conducted with healthy populations, often composed of young men and in Asia. Therefore, our results allow us to extend the positive effects of FB to a more specific population: patients with somatic functional syndromes such as FM and CFS/ME from the Mediterranean area. In this sense, our results are consistent with data obtained in the study of Muro et al. (2023) in which they concluded that FB in a Mediterranean forest increases psychological well-being in a sample of healthy adults compared to a control hiking group.

To our knowledge, only one study explored the benefits of walking in a Mediterranean forest among patients with FM. Unlike our study, which lasted only one session and was conducted in a relatively young forest (i.e., due to recent human action (e.g., fires, grassland), most of the mountain range is covered by aleppo pine forests and not by its original coastal holm oak grove forest), the López-Pousa et al. (2015) study explored a two-week intervention in two types of Mediterranean forests (mature and young) among FM patients López-Pousa et al. (2015) concluded that an aerobic exercise program consisting of walking through a forest could reduce FM symptoms. But, only in the mature forest did participants experience a subjective perception of having fewer days of pain and insomnia and more days of wellness. Unlike them, we did not find differences in terms of pain. It could be because our FM session only lasted 3 hours, and perhaps more time is needed to obtain results in this highly resistant clinical outcome. Therefore, the duration of the nature exposure could be a significant factor influencing the effectiveness of the intervention, as it has been previously suggested by (Antonelli et al. 2019)

Regarding the pain outcome, contrary to our results, Han et al. (2016) reported changes in pain perception following forest therapy among a sample of adults who suffered from chronic pain. Several differences between our study and the study of Han et al. (2016) could explain the discrepancy in the results. The intervention of Han et al. lasted for two days and included other components apart from FB, such as psychoeducation or time for socialization. It is assumed that the FB intervention is more beneficial when combined with other types of activities and when it has a longer duration.

Another promising result observed after FB was the significant improvement in the CFS/ME core symptom of fatigue (moderate effect size) and, parallelly, the opposite aspect of vigor (large effect size). This result is in line with other research on the benefits of walking in the woods to reduce fatigue in FM and CFS/ME (López-Pousa et al. 2015; Zhu et al. 2021) Forest bathing, by providing a sensory-rich environment that engages multiple modalities of perception within a natural context in the forest has been shown to stimulate the parasympathetic nervous system and reduce sympathetic activity, resulting in a state of greater well-being and vitality (Siah et al. 2023)

Limitations and Future Directions

The present study has some strengths that deserve to be stated. Mainly, the sample size (n = 44) was larger than the other study conducted on individuals with FM (n = 30, López-Pousa et al. 2015) and the evaluation protocol included a thorough evaluation of the impact of the FB session at the mental health and well-being level. Furthermore, a multidisciplinary team conducted the intervention, including two specialized psychologists and a mountain guide. However, the present study presents limitations that should also be acknowledged. The first one is not having a control group which impedes establishing causality. The inclusion of a control group (e.g., a psychoeducative control group) will be considered in future studies to assess the intervention's effectiveness. Another consideration was the short duration of the FB protocol (only one session) and the lack of a follow-up assessment to evaluate the stability of the observed improvements. Furthermore, further studies should also consider potential moderators (e.g., gender, age, physical fitness) and mediators (e.g., self-efficacy, self-esteem, nature connectedness) in explaining the beneficial effects of FB. In addition, the sample included only women. Although our results are interesting to generalize those of previous studies that only included males, future studies should extend and compare the benefits of FB in a clinical sample of men and women.

In conclusion, FB seems an affordable practice that may be useful for managing symptomatology in patients with FM and CFS/ME. Further research is needed to evaluate its effectiveness compared to other therapeutic approaches and to investigate further mechanisms of change associated with FB benefits.

The current study aimed to explore nature's benefits on individuals with FM and/or CFS/ME. The results from this study indicated that a 3-hour session of FB, conducted in a Mediterranean forest in patients with chronic pain and FM, could be beneficial for improving mental health and psychological well-being. FB could be an accessible and low-cost add-on therapeutic program which could be integrated into standard treatments for chronic pain and increase its efficacy and improve psychological distress in chronic pain patients. Further randomized controlled trials will be welcome comparing the effects of FB with other recognized therapeutic approaches for FM and/or CFS/ME (e.g., cognitive behavioral therapy, indoor therapeutic exercise). Furthermore, moderators (e.g., session duration) and mediators of change (e.g., changes in state mindfulness) of FB would be explored in future studies.

Acknowledgements

AF-S and AM acknowledge the funding from the Serra Húnter program (UAB-LE-8015 and UAB-LE-603, respectively). The project has been funded in part by the Spanish Ministry for Science and Innovation (MCIN) State R + D + I Program Oriented to the Challenges of Society (ref. PID 2020-117667RA-I00) and co-financed with European Union ERDF funds. We are grateful to the CIBER of Epidemiology and Public Health (CIBERESP CB22/02/00052; ISCIII) for its support.

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The Psychological Benefits of Forest Bathing in Individuals with Fibromyalgia and Chronic Fatigue Syndrome/ Myalgic Encephalomyelitis: A Pilot Study

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