Forest bathing in cardiovascular diseases – a narrative review
DOGARU Gabriela
1."Iuliu Hatieganu" University of Medicine and Pharmacy, Cluj-Napoca, Romania
2.Clinical Rehabilitation Hospital, Cluj-Napoca, Romania
Corresponding author: DOGARU Gabriela, E-mail: dogarugabrielaumf@gmail.com
Balneo Research Journal DOI: http://dx.doi.org/10.12680/balneo.2020.356 Vol.11, No.3, September 2020 p: 299–303
Peer reviewer: Olga SURDU, Romanian Association of Balneology, office@bioclima.ro
Abstract
Introduction.People of all ages have always enjoyed the forest, due to the peaceful environment, mild climate,
extremely beautiful landscapes, fresh air, pleasant flower and plant scents. Over the past years, a new medical science
termed forest medicine has developed, as an interdisciplinary science belonging to the fields of alternative medicine,
environmental medicine and preventive medicine, which comprises the effects of forest environments on human
health. However, beyond its use for pleasure, there is increasing evidence suggesting that the forest can offer very
many benefits for health, including in cardiovascular diseases. Objectives.To bring to attention a less known and
studied therapeutic issue, i.e. the effects of forest bathing on the human body, especially in cardiovascular diseases.
Material and method. Given the heterogeneous nature of the evidence in the literature, these findings should be put
together in order to allow an adequate interpretation. Thus, we reviewed the observational clinical studies (on
prospective cohorts, case-control studies, retrospective cohorts), the randomized controlled trials (RCT) and non-
randomized controlled trials in PubMed, over the past 20 years, until June 2020, focusing on the effects of the forest in
cardiovascular diseases. The search terms included forest, forest bathing, cardiovascular effects, blood pressure,
diabetes mellitus, coronary artery disease, stress, psychological effects. Results and discussions.The results of the
studies show that the benefits of the forest on the cardiovascular system are obvious regardless of age, sex,
socioeconomic environment or previous exposure to a natural environment. Also, walking in the forest environment
can promote cardiovascular relaxation by facilitating the parasympathetic nervous system and by suppressing the
sympathetic nervous system. In addition, forest therapy can be effective in reducing negative psychological symptoms.
The current literature supports the benefits of exposure to nature and green environments for human health, through
the effects on: the immune system (increase of natural killer cells/cancer prevention); the cardiovascular system
(hypertension/coronary artery disease); the respiratory system (allergies and respiratory diseases); depression and
anxiety (mood disorders and stress); mental relaxation. Conclusions.The studies conducted show the cardiovascular
benefits associated with continuous immersion in nature, but further research regarding this aspect is definitely
required.
Key words: forest, forest bathing, cardiovascular effects, blood pressure, forest walking,
Introduction
People of all ages have always enjoyed the forest,
due to the peaceful environment, mild climate,
extremely beautiful landscapes, fresh air, pleasant
flower and plant scents. In Japan, starting with 2004,
a lot of studies have been conducted to investigate
the effects of forest environments on human health.
Over the past years, a new medical science termed
forest medicine has developed, as an
interdisciplinary science belonging to the fields of
alternative medicine, environmental medicine and
preventive medicine, which comprises the effects of
forest environments on human health (1).
In Germany, for the first time in Europe, healing
forests have been developed and cultivated in the
Mecklenburg-Vorpommern area. Also, in
Heringsdorf on the Baltic Sea coast, Germany has
already created a first spa resort with forest bathing
indications. Studies conducted in transcontinental
Japan and China have evidenced a multitude of
physiological and psychological benefits associated
with the practice of Shinrin-Yoku (SY), known as
forest bathing. SY is a traditional Japanese practice
of immersion in nature through all five senses. In the
1980’s, SY emerged in Japan as an essential
component of preventive and curative medicine (1).
The popularization of forest bathing in Japan
through easy access to the forest environment and
governmental recommendations resulted in a
reduction of acute psychological disorders due to the
time spent in green spaces (1).
299
Objectives.To bring to attention a less known and
studied therapeutic issue, i.e. the effects of forest
bathing on the human body, especially in
cardiovascular diseases.
Material and method.
However, beyond its use for pleasure, there is
increasing evidence suggesting that the forest can
offer very many benefits for health. Over the past
decade, a considerable number of findings from
various countries regarding the potential benefits of
the forest on health, as well as the possible
biological mechanisms underlying these effects have
been reported. Given the heterogeneous nature of the
evidence in the literature, these findings should be
put together in order to allow an adequate
interpretation. Thus, we reviewed the observational
clinical studies (on prospective cohorts, case-control
studies, retrospective cohorts), the randomized
controlled trials (RCT) and non-randomized
controlled trials
Search strategy. For our research, we used the
PubMed database. We selected and evaluated all the
articles resulting from a systematic search. The
search was aimed at finding articles published over
the past 20 years, from 2000 to 2020, using a certain
key word combination. The search terms included
forest, forest bathing, cardiovascular effects, blood
pressure, diabetes mellitus, coronary artery disease,
stress, psychological effects.
Selection criteria. We used several inclusion criteria:
a) articles written in English; b) studies of the effects
of forest bathing on cardiovascular diseases; c)
studies in which the forest was used as a
complementary therapy. We also used exclusion
criteria: a) articles reporting no data; b) studies
conducted on animals; c) effects of the forest on
stress and psychological effects.
Data extraction. A screening of the titles found using
the search strategy, without any difference in their
findings, was performed. The articles relevant for
the subject of the present study were selected using
the inclusion and exclusion criteria. A total number
of 21 articles were found. After the application of
both inclusion and exclusion criteria, 8 articles were
excluded because they were not relevant for our
subject, presenting only effects on stress and
psychological effects. The other 13 articles were
analyzed and after being read, they were all taken
into consideration for the current study. Some
studies showed the use of forest bathing in certain
cardiovascular diseases.
Results and discussions
Forest bathing can be considered a form of nature
therapy. According to the model of Song, Ikei and
Miyazaki (2), the concept of nature therapy clearly
defines “a set of practices aimed at achieving
“preventive medical effects” through exposure to
natural stimuli that confer a state of physiological
relaxation and improve the weakened immune
functions to prevent diseases”. The conceptual
model of nature therapy starts with a “state of stress”
and then highlights the “restorative effects” of nature
(forests, flowers, etc.) in which an improvement of
“physiological relaxation” and “recovery of immune
function” (with individual differences) is
hypothesized. These responses to nature are
subsequently incorporated in the model of evidence-
based medicine (EBM), leading to the “preventive
medical effect” (2).
Studies over the past 10 years regarding the effects
of the forest on the cardiovascular system and the
autonomic nervous system (ANS) started with basic
cardiac monitoring, then involved the correlation of
the monitored cardiac parameters with the
parasympathetic nervous system (PNS), the
sympathetic nervous system (SNS), and
subsequently, more extensive studies on the effects
of SY on specific pathological conditions: arterial
hypertension (HTN), coronary artery disease (CAD),
and chronic obstructive pulmonary disease (COPD)
(1).
The aim of a study (3) was to examine the
physiological effects of forests on autonomic
nervous activity. Twelve male students (21.8 ± 0.8
years) were included in the study; six subjects were
sent to a forest area and the other six, to an urban
area. The heart rate variability (HRV), blood
pressure and pulse rate were measured as
physiological indices. The results showed that the
pulse rate and diastolic blood pressure were
significantly lower in subjects in the forest area
compared to those in the urban area, the forest
allowing effective relaxation of the humans (3).
According to another study (4), 625 Japanese men
from 57 forest locations and 57 urban locations in
Japan had an 80% increase in the parasympathetic
indicators of HRV in the case of forest locations,
demonstrating in this way that the forest was more
effective in reducing stress indicators than the urban
environment. Blood pressure and PR also decreased
in the forest environment compared to the urban
environment (4).
300
It is considered that the evolution of information
technology causes great stress to modern people, and
controlling this stress can become an important
problem. The aim of a study was to examine the
psychological and physiological benefits of the
interaction with indoor plants. The study subjects
were 24 young male adults aged 24.9 ± 2.1 years.
The first group (12 subjects) performed indoor plant
gardening tasks, while the second group (12
subjects) performed a computer task. Psychological
evaluation was carried out using the semantic
differential method (SDM), and physiological
evaluation was based on heart rate variability and
blood pressure. The results of the study suggested
that active interaction with indoor plants can reduce
physiological and psychological stress compared to
mental work. This occurs by suppression of the
sympathetic nervous system activity and diastolic
blood pressure, and promotion of comfortable, calm
and natural feelings (5).
The study of Tsunetsugu et al. (6), conducted in 12
male students aged between 21 and 23 years (mean
+/- SD: 22.0 +/- 1.0 years), investigated the
physiological effects of “Shinrin-yoku” by assessing
blood pressure, pulse, heart rate variability (HRV),
salivary cortisol concentration and salivary
immunoglobulin A. Subjective feelings of being
“comfortable”, “calm” and “refreshed” were also
evaluated by a questionnaire. The results showed
that in the forest area compared to the urban area,
blood pressure and pulse rate were significantly
lower, and salivary cortisol concentration was
significantly decreased. These physiological
responses suggest that sympathetic nervous system
activity was suppressed and that parasympathetic
nervous system activity was improved in the forest
area, and also, that “Shinrin-yoku” reduced the stress
level. Based on subjective evaluation, the
“comfortable”, “calm” and “refreshing” feelings
were significantly greater in the forest area (6). Also,
a study on 17 women aged over 40 years conducted
by Ochiai et al. (7) found a global reduction of heart
rate (HR) after a one-day forest therapy program.
These studies demonstrate cardiovascular benefits
for both sexes. Kardan et al. (8) performed a
correlation analysis of the data acquired by the
Canadian Ontario Health Study. The high-resolution
satellite images showed that residents in areas with a
higher tree density suffer from fewer
cardiometabolic diseases than residents in areas with
fewer trees (8). The benefits of SY on the
cardiovascular system are obvious regardless of age,
sex, socioeconomic environment or previous
exposure to a natural environment (1).
A significant number of studies have evidenced the
effects of SY and nature therapy (NY) on specific
pathological conditions, including HTN, CAD,
COPD and type 2 diabetes mellitus (DMII). The
study carried out by Mao et al. (9) aimed to provide
scientific evidence supporting the efficacy of forest
bathing as a natural therapy for arterial hypertension.
Thus, 24 elderly patients diagnosed with essential
hypertension were randomized to two groups of 12
patients. A group was sent to a forest to experience a
7 day/7 night trip, and the other group was sent to a
city in the Hangzhou area for control. Blood
pressure indicators, pathological factors related to
cardiovascular diseases, including endothelin-1,
homocysteine, renin, angiotensinogen, angiotensin
II, angiotensin II type 1 receptor, angiotensin II type
2 receptor, as well as the inflammatory cytokines
interleukin-6 and tumor necrosis α were measured.
The results of the study showed that subjects
exposed to the forest environment had a significant
reduction of blood pressure compared to the urban
group; the bioindicator values of the subjects
exposed to the forest environment were also lower
than those of the subjects in the urban control group
and their baseline levels (9).
In order to test the hypothesis that walking in a
park has a greater positive effect on the
hemodynamic parameters of patients with coronary
artery disease (CAD) than walking in an urban
environment, a study on 20 stable patients with CAD
was conducted. These were randomized to two
groups: 30 minutes of walking for 7 consecutive
days in a city park or on a busy street. The Wilcoxon
signed test was used to study the short-term changes
(30 min) and cumulative changes (after 7
consecutive days of exposure) in hemodynamic
parameters at rest in different environments. It was
concluded that walking in a park had a greater
positive effect on the cardiac function of patients
with CAD than walking in an urban environment,
which suggests that cardiac rehabilitation by
walking in green areas following coronary events
should be encouraged (10).
Another study (11) determined the effects of forest
bathing on elderly patients with chronic obstructive
pulmonary disease (COPD), through a reduction of
inflammation and stress hormones. The patients
were randomized to two groups. One group was sent
to the forest and the other one was sent to a control
urban area.
301
Flow cytometry and stress hormones were evaluated.
In the forest group, a significant decrease in perforin
and granzyme B expression was found, accompanied
by a reduction of proinflammatory cytokines and
stress hormones.
In a longitudinal study including 48 adults diagnosed
with DMII, it was found that blood glucose values
decreased after multiple SY sessions, indicating a
significant correlation between SY and the reduction
of blood glucose levels (1, 12). In another study, 48
participants, 16 men and 32 women, with a mean
age of 66.8 years, diagnosed with DMII, walked 3 to
6 km nine times a week over a period of 6 years.
There were no statistically significant differences in
the glucose levels or the HbA1c levels of the
subjects between the shorter and longer walks.
However, the mean blood glucose levels in both
groups before and after the forest walks decreased
by 79 ± 10 mg/dL and 76 ± 7 mg/dL respectively
(1,13).
Despite the increasing attention paid to forest
therapy as an alternative therapy, there is very little
evidence of its therapeutic effects. Consequently, a
study focused on clarifying the health benefits of
forest walking regarding cardiovascular reactivity.
Forty-eight young adult men participated in the
study for two days. Heart rate variability (HRV) was
measured to investigate physiological reactivity to
walking as an indicator of autonomic nervous
activity. Based on the frequency analysis of the RR
interval, high frequency (HF) data were used as an
indicator of parasympathetic nervous activity, and
the low frequency/high frequency (LF/HF) ratio was
used as an indicator of sympathetic nervous activity.
Heart rate was also investigated using R-R interval
data. HRV and cardiac rhythm were continuously
recorded during walking. Statistical analysis showed
the fact that forest walking significantly increased ln
(HF) values and significantly decreased ln (LF/HF)
values compared to urban walking. Heart rate during
forest walking was significantly lower than in the
control group. The conclusion of the study was that
forest walking can promote cardiovascular
relaxation by facilitating the parasympathetic
nervous system and suppressing the sympathetic
nervous system. In addition, forest therapy can be
effective in reducing negative psychological
symptoms (1).
The current literature supports the benefits of
exposure to nature and green environments for
human health, through the effects on: the immune
system (increase of natural killer cells/cancer
prevention); the cardiovascular system
(hypertension/coronary artery disease); the
respiratory system (allergies and respiratory
diseases); depression and anxiety (mood disorders
and stress); mental relaxation. Nature therapy as a
health promotion method and a universal health
model is involved in reducing the “state of stress”
and “technostress” of our days (1). Western
researchers are invited to conduct empirical studies
regarding the therapeutic benefits associated with
forest bathing and health care service
providers/students are encouraged to take into
consideration its practice to reduce stress and
potential disconnection (1).
In Romanian spa resorts, climate therapy is
indicated in the form of: heliotherapy by exposure of
the body to solar radiation (infrared and ultraviolet
radiation) for prophylactic and/or therapeutic
purposes; aerotherapy by partial or total outdoor
exposure without solar radiation (in the shade or
during hours/days without sun); walking, which is a
form of movement therapy, associated with
aerotherapy. For walking, standardized routes are
established regarding the length, the level difference,
the slopes included, the walking pace, depending on
the disease. The walking routes are marked, placed
in forest areas with attractive landscape elements
(14,15,16). The natural therapeutic factors consisting
of carbonated mineral water baths, mofettes, climate
therapy, through forest walking along with medical
physical culture, indicated in the rehabilitation of
post-stroke patients, had a beneficial effect on
clinical and functional symptoms, improving the
quality of walking and balance, functionality in a
patient who suffered a stroke five years before and
was followed up for three years, during participation
in an annual medical rehabilitation program. The
rehabilitation treatment including walking improves
quality of life in post-stroke survivors (16,17), as
well as in patients with chronic obliterative
arteriopathy (18).
Conclusions
The studies conducted show the benefits associated
with continuous immersion in nature on some
cardiovascular diseases, but this aspect definitely
requires further research. Global studies are needed
in order to provide new evidence of the relationship
between the forest – forest bathing – and clinical
therapeutic effects.
302
References
1. Margaret M. Hansen, Reo Jones and Kirsten
Tocchini. Shinrin-Yoku (Forest Bathing) and
Nature Therapy: A State-of-the-Art Review.
Int J Environ Res Public Health. 2017 Aug;
14(8): 851. doi: 10.3390/ijerph14080851.
2. Song, C.; Ikei, H., Miyazaki, Y. Physiological
Effects of Nature Therapy: A Review of the
Research in Japan. Int. J. Environ. Res. Public
Health ; 2016 Aug 3;13(8):781. doi:
10.3390/ijerph13080781.
3. Park, B.- J., Tsunetsugu, Y.; Kasetani, T.,
Morikawa, T., Kagawa, T., Miyazaki, Y.
Physiological effects of forest recreation in a
young conifer forest in Hinokage Town,
Japan. Silva Fenn. 2009; 43: 291–301.
4. Kobayashi H., Song C., Ikei H., Kagawa T.,
Miyazaki Y. Analysis of Individual Variations
in Autonomic Responses to Urban and Forest
Environments. Evid. Based Complement.
Altern.
Med. 2015:671094.
doi:
10.1155/2015/671094.
5. Lee, M., Lee, J., Park, B., Miyazaki, Y.
Interaction with indoor plants may reduce
psychological and physiological stress by
suppressing autonomic nervous system activity
in young adults: A randomized crossover
study. J. Physiol. Anthropol. 2015 Apr
28;34(1):21. doi: 10.1186/s40101-015-0060-8.
6. Tsunetsugu, Y., Park, B., Ishii, H., Hirano, H.,
Kagawa, T., Miyazaki, Y. Physiological
effects of Shinrin-yoku (taking in the
atmosphere of the forest) in an old-growth
broadleaf forest in Yamagata Prefecture,
Japan. J. Physiol. Anthropol. 2007;26: 135–
142.
7. Ochiai, H., Ikei, H., Song, C., Kobayashi, M.,
Miura, T., Kagawa, T., Li, Q., Kumeda, S.,
Imai, M., Miyazaki, Y. Physiological and
Psychological Effects of a Forest Therapy
Program on Middle-Aged Females. Int. J.
Environ. Res. Public Health .2015; 12:15222–
15232.
8. Kardan, O., Gozdyra, P., Misic, B., Moola, F.,
Palmer, L.J., Paus, T., Berman, M.G.
Neighborhood greenspace and health in a large
urban center. Sci. Rep..2015;5:1–14.
9. Mao, G., Cao, Y., Lan, X., He, Z., Chen, Z.,
Wang, Y., Hu, X., Lv, Y., Wang, G., Yan, J.
Therapeutic effect of forest bathing on human
hypertension
in
the
elderly. J.
Cardiol. 2012; 60:495–502.
10. Grazuleviciene, R., Vencloviene, J., Kubilius,
R., Grizas, V., Dedele, A., Grazulevicius, T.,
Ceponiene, I., Tamuleviciute-Prasciene, E.,
Nieuwenhuijsen, M.J., Jones, M., et al. The
Effect of Park and Urban Environments on
Coronary Artery Disease Patients: A
Randomized
Trial. BioMed
Res.
Int. 2015;2015:403012.
doi:
10.1155/2015/403012.
11. Jia, B.B., Yang, Z.X., Mao, G.X., Lyu, Y.D,
Wen, X.L., Xu, W.H., Lyu, X.L., Cao, Y.B.,
Wang, G.F. Health Effect of Forest Bathing
Trip on Elderly Patients with Chronic
Obstructive Pulmonary Disease. Biomed.
Environ. Sci. 2016 ;29:212–218.
12. Ohtsuka, Y. Walking in a Forest Is Beneficial
for Type 2 Diabetic Patients; Li, Q., Ed.;
Forest Medicine; Nova: Hauppauge, NY,
USA, 2012; pp. 109–114.
13. Ohtsuka, Y. Effect of the Forest Environment
on Blood Glucose; Li, Q., Ed.; Forest
Medicine; Nova: Hauppauge, NY, USA, 2012;
pp. 109–114.
14. Constantin Munteanu, Gabriela Dogaru.
Bioclimatologie: Bioclimatologie umană.
Bucureşti: Editura Balneară,2020.
15. Gabriela Dogaru, Constantin Munteanu.
Mofete: Gaze terapeutice. Bucureşti: Editura
Balneară, 2020.
16. Munteanu Constantin, Munteanu Diana,
Hoteteu Mihail, Dogaru Gabriela.
Balneotherapy – Medical, Scientific,
Educational And Economic Relevance
Reflected By More Than 250 Articles
Published In Balneo Research Journal. Balneo
Research Journal. 2019;10(3):174–203.
17. Gabriela Dogaru, Alexandra Ispas, Ioana
Stănescu, Marieta Motricala, Molnár Ákos. A
clinical study on the efficacy of natural
therapeutic factors in Băile Tuşnad for the
rehabilitation of post-stroke patients. Balneo
Research Journal. 2017;8(1):5-10.
18. Gabriela Dogaru, Ioana Stănescu, Daniela Pop,
Marieta Motricală, Molnár Ákos. Effects of
carbonated mineral water treatment in Băile
Tuşnad on chronic arterial occlusive disease –
a case report. Balneo Research Journal.
2017;8(3):121-124.
303