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REVIEW ARTICLE Open Access
Medical empirical research on forestbathing (Shinrin-yoku): a systematic reviewYe Wen1,2, Qi Yan1, Yangliu Pan1, Xinren Gu1* and Yuanqiu Liu1*
Abstract
Aims: This study focused on the newest evidence of the relationship between forest environmental exposure andhuman health and assessed the health efficacy of forest bathing on the human body as well as the methodologicalquality of a single study, aiming to provide scientific guidance for interdisciplinary integration of forestry andmedicine.
Method: Through PubMed, Embase, and Cochrane Library, 210 papers from January 1, 2015, to April 1, 2019, wereretrieved, and the final 28 papers meeting the inclusion criteria were included in the study.
Result: The methodological quality of papers included in the study was assessed quantitatively with the Downsand Black checklist. The methodological quality of papers using randomized controlled trials is significantly higherthan that of papers using non-randomized controlled trials (p < 0.05). Papers included in the study were analyzedqualitatively. The results demonstrated that forest bathing activities might have the following merits: remarkablyimproving cardiovascular function, hemodynamic indexes, neuroendocrine indexes, metabolic indexes, immunityand inflammatory indexes, antioxidant indexes, and electrophysiological indexes; significantly enhancing people’semotional state, attitude, and feelings towards things, physical and psychological recovery, and adaptive behaviors;and obvious alleviation of anxiety and depression.
Conclusion: Forest bathing activities may significantly improve people’s physical and psychological health. In thefuture, medical empirical studies of forest bathing should reinforce basic studies and interdisciplinary exchange toenhance the methodological quality of papers while decreasing the risk of bias, thereby raising the grade of paperevidence.
Keywords: Forest bathing (Shinrin-yoku), Systematic review, Methodology
IntroductionSubhealth is a third state between health and disease.The most common symptoms of subhealth are fatigue,poor sleep quality, forgetfulness, physical pain, and sorethroat, and subhealth also increases the risk of infectionand degrades the capacity of the immune system [1, 2].With the rapid development of the global economy andurbanization, increasing numbers of people have begunto show subhealth symptoms. In a survey conducted bythe Ministry of Health, Labor and Welfare of Japan (32,000 Japanese people over 12 years old), 54.2% of respon-dents considered their stress levels to be “very high” or“relatively high” [3]. It is estimated that one third of
American adults have nighttime sleep problems everyweek, and between 50 and 70 million people complainthat nighttime sleep deprivation is mediated by daytimeimpairment [4, 5]. A meta-analysis showed that betweenone third and one half of the population in the UK wasaffected by chronic pain, and the incidence of chronicpain in different body parts among adult residents was35.0–51.3%, and the incidence of chronic pain increasedwith age [6]. Under the background of the increasingnumber of people with subhealth around the world, for-est bathing (Shinrin-yoku) therapy came about, whichnot only brings people with subhealth a healthy lifestyleadvocated by modern medicine but also offers comple-mentary therapies to the sick [7]. The term forest bath-ing was created in 1982 by the Ministry of Agriculture,Forestry and Fisheries of Japan [8]. It refers to a healing
© The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
* Correspondence: [email protected]; [email protected] of Forestry, Jiangxi Agricultural University, 1101 ZhiMin Road,Nanchang 330045, ChinaFull list of author information is available at the end of the article
Environmental Health andPreventive Medicine
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 https://doi.org/10.1186/s12199-019-0822-8
technique that restores the physical and psychologicalhealth of the human body through a “five senses experi-ence” (vision, smell, hearing, touch, and taste) when thebody is exposed to a forest environment. Forest bathinghas positive effects on human physical and mental health[9, 10], especially in enhancing immunity, treating chronicdiseases, regulating mood, and reducing anxiety and de-pression [11–14]. More benefits can be gained from exer-cising or meditating in a forest environment than in anurban environment [15, 16]. In recent years, althoughmedical empirical research on forest bathing has increasedgradually, its healthcare mechanism for the human bodyhas not been clearly defined due to a lack of research re-sults, a low level of evidence, and a disciplinary barrier. Al-though forestry scholars and medical scholars have carriedout relevant research on forest bathing therapy, there arestill some limitations due to different research focuses. (1)The theoretical basis of research varies. Medical scholarsmainly take evidence-based medicine as the theoreticalbasis for studying the physiological and psychologicalstress response of the human body during exposure to theforest environment to demonstrate the health-related ef-fects of forest bathing. Forestry scholars mainly study thehealth mechanism of forest environmental factors and therelationship among them based on the theory of forestry.(2) The subject of research varies. The research subject ofmedical scholars is the human body, through studyingchanges in physiological and psychological indicators todirectly verify the health-related effects of forest bathing.The research subject of forestry scholars is the forest en-vironment, through the study of forest environmental fac-tors of different variables to indirectly prove the healthbenefits of forest bathing. To solve this problem, this studyuses the evidence-based medicine system evaluationmethod to qualitatively integrate the research results. Theobjectives are as follows: (1) focus on the latest evidenceof the relationship between forest environment exposureand human health, (2) assess the methodological qualityof individual studies, and (3) provide scientific theoreticalguidance for the interdisciplinary integration of forestryand medicine.
MethodsSelection criteria(1) Interventional study on the health effects of forestbathing. (2) Number of intervening measures is less thanor equal to 3. (3) Trial was carried out in a forest envir-onment. (4) The study period of the paper was fromJanuary 1, 2015, to April 1, 2019. (5) The paper is writ-ten in English. (6) Subjects are human.
Paper searchThrough computer retrieval of PubMed, Embase, andCochrane Library, we screened medical empirical research
papers on forest bathing published in the last 5 years, andused a citation traceability method and Google academicsearch for papers that needed to be supplemented. In thisstudy, the combination of subject words and free wordswas adopted, and the logical character “OR” was used tolink each search term to obtain final search results. Searchterms are shown in Table 4 in Appendix.
Paper screening and data extractionPaper preliminary screening was conducted independentlyby one researcher through reviewing titles and abstracts,and data extraction was conducted independently by tworesearchers. After extraction, cross-checking was con-ducted, and disputes were resolved through discussion orreferring to third-party opinions. Data extraction includesauthor name, publication year, study design, participantprofile, ethical review, sample size, intervention measures,control measures, measurements, and outcomes.
Quality assessment toolThe methodological quality of the included studies wasassessed using the Downs and Black checklist [17], whichwas used for quantitative evaluation of the quality ofpapers in randomized controlled trials (RCTs) and non-randomized controlled trials (NRCTs). The evaluationincluded 27 items from 5 aspects of the paper: reporting,external validity, bias, confounding, and power. The evalu-ation was carried out by two researchers independently,and any disputes could be resolved through discussion orby referring to the opinions of a third party. The systemevaluation report was prepared according to the PreferredReporting Items for Systematic Reviews and Meta-Analyses [18] declaration standard.
ResultsSearch resultsInitially, 210 papers were searched, and 17 duplicate pa-pers and 133 irrelevant papers were removed based ontitle and abstract. Subsequently, we evaluated the fulltext and excluded 32 papers. Finally, 28 papers met thecriteria for inclusion in the study. The screening processis shown in Fig. 1.
General characteristicsGeneral characteristics of the included studies are shownin Table 1. A total of five countries or regions, includingJapan, South Korea, Poland, China, and Taiwan, haveconducted empirical studies on the health effects offorest bathing [19–46], among which 27 studies wereconducted in Asian countries [19–34, 36–46] and 1study [35] in a European country. Japanese scholars hadthe largest number of studies, publishing 13 papers [19,20, 22–25, 28, 31, 38, 40, 42–44], accounting for 46% ofthe total number of included studies, followed by
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 2 of 21
Chinese, South Korean, Taiwanese, and Polish scholars,publishing 6 papers [27, 32, 37, 39, 45, 46], 5 papers [21,26, 29, 30, 34], 3 papers [33, 36, 41], and 1 paper [35],respectively, accounting for 21%, 18%, 11%, and 4% ofthe total number of included studies, respectively.Among them, there were 17 RCTs [20, 21, 24–27,30–32, 35, 37–40, 43, 45, 46], accounting for 61% ofthe total number of included studies, and 11 NRCTs[19, 22, 23, 28, 29, 33, 34, 36, 41, 42, 44], accountingfor 39% of the total number of included studies. Theparticipants were dominated by healthy people, with atotal of 17 studies [20, 24, 26, 29, 31, 33–38, 40, 42–46],accounting for 61% of the total number of studies in-cluded, and mostly young people aged 18–30. There were11 studies [19, 21–23, 25, 27, 28, 30, 32, 39, 41] on peoplewith health problems, accounting for 39% of the totalnumber of studies, most of which were middle-aged andelderly people over 45 years old. There were 13 studies[19, 21, 24, 29–31, 33, 34, 37, 38, 40, 43, 45] with morethan 50 samples, accounting for 46% of the total numberof included studies, 8 studies [20, 22, 23, 25, 27, 36, 41, 44]with less than 20 samples and 7 studies [26, 28, 32, 35, 39,42, 46] with 20–50 samples, accounting for 29% and 25%of the total number of included studies, respectively.There were 20 forest bathing studies [19, 20, 22–26, 28,31, 33, 35–38, 40, 42–46] that lasted for 1–3 days,
accounting for 71% of the total number of included stud-ies. There were 8 forest bathing studies [21, 27, 29, 30, 32,34, 39, 41] that lasted for more than 3 days, accounting for29% of the total number of included studies. Mostscholars have taken ethical considerations into accountwhen carrying out research. A total of 25 studies [19, 20,22–44] have passed the ethical review, accounting for 89%of the total included studies. This was not mentioned in 3studies [21, 45, 46], accounting for 11% of the total num-ber of included studies. There were 3 interdisciplinarystudies [44–46], accounting for 11% of the total includedstudies.
Intervention measures and control measuresThe detailed characteristics of the included research pa-pers are shown in Tables 2 and 3. All studies take forestor urban environment exposure as the trial premise, andmore than one or two intervention measures areadopted to carry out the trial, and some control mea-sures are imposed. The interventions are mostly walking,meditation, yoga, Pilates, sightseeing, and crafts. The“five senses experience” and exercise are at the core. Thecontrol measures of each study are similar, mainly in-cluding the following: (1) control trial time and activityspace; (2) prohibit or control tobacco, alcohol, and caf-feine intake; (3) prohibit or allow use of drugs and
Fig. 1 Flow diagram of the screening process
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 3 of 21
electronic products; (4) control of accommodation anddiet; (5) consideration of female physiological period fac-tors; and (6) increase buffer time (many hours or days)in a cross-over study to prevent carryover effect.
Evaluative measuresThe evaluative measures for the healthcare effect of for-est bathing are generally divided into self-reported mea-sures and physiological measures according to differentresearch purposes for choosing the appropriate evalu-ative measures, both of which can reflect the psycho-logical and physiological stress response of the humanbody. Self-reported measurement combined with physio-logical indicators was the largest research method andused a total of 16 studies [19, 20, 22, 23, 25–30, 32–34,36, 37, 43], accounting for 57% of the total includedstudies. There are 6 studies each that only use self-reported measurement [21, 35, 40, 44–46] or physio-logical indicator measurement [24, 31, 38, 39, 41, 42],each accounting for 21.5% of the total number of in-cluded studies. Self-reported measurement is widelyused because it is simple to measure and easy to conductquantitative analysis. Currently, internationally acceptedself-reported measurement has been applied in the
empirical research of forest bathing. Some scholars alsouse a homemade scale for research [45, 46]. In physio-logical measures, due to the limitation of the trial envir-onment, blood, urine, or saliva samples that requirestrict storage time and temperature are generally col-lected on the spot before and after the forest bathing, orat a place with good medical conditions according to thedifferent testing items. Physiological indicators such asblood pressure, heart rate, pulse, and brain waves aregenerally measured by portable instruments.
Physiological responseCardiovascular function and hemodynamic indexesThere were 8 studies [19, 22, 28, 29, 33, 36, 37, 39] in-volving blood pressure, and systolic blood pressure(SBP) and diastolic blood pressure were significantly re-duced in 4 of these studies [19, 22, 33, 37], while onlySBP was significantly decreased in 1 study [24], and onlySBP was significantly increased in 1 study [15]. Therewere 4 studies [23, 28, 33, 36] in which pulse was signifi-cantly decreased. There were 3 studies [20, 25, 43] in-volving heart rate, which was significantly decreased in 2studies [25, 43]. There were 7 studies [20, 25, 29, 33, 34,38, 43] involving heart rate variability (HRV); the naturallogarithmic value of the high frequency (lnHF) of HRVwas significantly increased in 4 studies [20, 25, 38, 43],and the natural logarithmic value of the low frequency(lnLF)/lnHF of HRV was significantly decreased in 2studies [38, 43]. There were 2 studies [32, 39] in whichbrain natriuretic peptide was significantly decreased.There was 1 study [32] in which Endothelin-1 was sig-nificantly decreased.
Neuroendocrine indexesThere were 3 studies [23, 27, 31] in which cortisol wassignificantly decreased. There were 3 studies [22, 27, 28]involving adrenaline, which was significantly decreasedin 2 studies [22, 27]. There was 1 study [28] involvingnorepinephrine and dopamine, which were significantlydecreased.
Metabolism indexesThere were 2 studies [28, 29] involving triglycerides,which were significantly decreased in 1 study [29]. Therewas 1 study [28] involving adiponectin, which was sig-nificantly increased.
Immune and inflammatory indexesThere were 2 studies [27, 41] involving nature killer(NK) cells, which were significantly decreased in 1 study[27]. There was 1 study [27] involving NKT-like cells,which were significantly decreased. There was 1 study[41] involving NK cell activity, which was significantlyincreased. There were 4 studies [26, 27, 32, 39] involving
Table 1 General characteristics of included studies (n = 28)
Characteristic Categories No. (%)
Country or region China 6 (21)
Korea 5 (18)
Japan 13 (46)
Poland 1 (4)
Taiwan 3 (11)
Research design RCT 17 (61)
NRCT 11 (39)
Participant Healthy people 17 (61)
People with health problems 11 (39)
Average age (years) 18 ≤ 1 (3.5)
> 18 ≤ 30 12 (43)
> 30 ≤ 45 1 (3.5)
> 45 12 (43)
Age unknown 2 (7)
Sample size ≤ 20 8 (29)
> 20 ≤ 50 7 (25)
> 50 13 (46)
Time 3 days≤ 20 (71)
> 3 days 8 (29)
Ethical consideration Yes 25 (89)
No 3 (11)
Interdisciplinary research Yes 3 (11)
No 25 (89)
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Table
2Med
icalem
piricalresearch
(n=25)
Autho
rs(year)
Research
design
Participants
Interven
tionmeasures
Con
trol
measures
Measuremen
tsandou
tcom
es
Trialg
roup
Con
trol
grou
pSelf-repo
rtmeasures
Physiologicalm
easures
Horiuchi
(2015)
[19]
NRC
T(before-afterstud
y)※
1)Respon
segrou
p:Male
andfemaleparticipants,
averageagewas
63.9
years(n
=27).2)
Non
-respon
segrou
p:Male
andfemaleparticipants,
averageagewas
61.6
years(n
=27).
N/A
Participantswereexpo
sed
toforesten
vironm
entand
theactivity
was
carried
outfor90
min
1)Participantswere
divide
dinto
2grou
psaccordingto
thechange
sof
meanarterialp
ressure
before
andafterforest
bathing(>5%
was
the
respon
segrou
p,<5%
was
theno
n-respon
segrou
p).
2)Someparticipantswere
givenmed
ications
for
hype
rten
sion
,diabe
tes,
hype
rlipide
mia,
hype
ruricem
ia,and
osteop
orosis.
3)Sm
okingandcaffeine
werebann
ed12
hbe
fore
thetrial,andalcoho
lwas
bann
ed24
hbe
fore
thetrial
1)Respon
segrou
pPO
MS:
D*↓
V*↑
T-A*↓
F*↓
C*↓
A-H*↓
2)Non
-respon
segrou
pPO
MS:
D*↓
V*↑
T-A*↓
F*↓
C*↓
A-H↓
1)Respon
segrou
p:SBP*↓
DBP*↓
Meanarterialp
ressure*↓
Salivaryam
ylase↓
2)Non
-respo
nsegrou
p:SBP*↓
DBP↓
Meanarterialp
ressure*↓
Salivaryam
ylase↑
Igarashi
(2015)
[20]
RCT
(cross-overstud
y)※
Femaleparticipants,
averageagewas
46.1
years(n
=4or
1)
Female
participants,
averageagewas
46.1years(n
=4
or1)
Afte
ra3-min
rest,the
participantssatand
watched
thekiwio
rchard
for10
min
(orthebu
ilding
site);aftera3-min
rest,the
participantssatand
watched
thebu
ildingsite
(orthekiwio
rchard),each
grou
pwas
askedto
view
2trialsites
1)Thetrialb
egan
inthe
summer.2)S
even
teen
participantsweredivide
dinto
fivegrou
ps.3)
Participantsavoide
dmen
struationanddidno
tdrinkor
smoke.4)
Livedin
thesubu
rbs.5)
Thetw
otrial
sitesarecloseto
each
othe
r
SDmetho
d:Com
fortable
feeling#↑
Naturalfeeling#↑
Relaxedfeeling#↑
POMS:
D# ↓
V#↑
T-A# ↓
F#↓
C# ↓
A-H
# ↓
lnHF#↑
lnLF/ln
HF↓
Heartrate↓
Kang
(2015)
[21]
RCT
Maleandfemale
participants,average
age
was
54.8years(n
=32)
Maleandfemale
participants,
averageagewas
50years(n
=32)
Inthemorning
,the
trial
grou
pandcontrolg
roup
wereexpo
sedto
the
foresten
vironm
entand
walkedfor2hIn
the
afternoo
n,thetrialg
roup
perfo
rmed
additio
nal
stretching
andintensive
exercisesfor4h
1)Thetrialb
egan
inlate
sprin
gandlasted
fivedays.
2)Participantsselection
criteria:A
dults
over
20years
ofagewith
posteriorne
ckpain
formorethan
3mon
ths,andVA
Sgrades
over
4
VAS:
VASon
thefirst
day*↓
VASon
theen
dday*↓
Cervicalrange
ofmotion*↑
Neckdisability
inde
x*↓
EuroQol
5D-3L
VAS*↑
EuroQol
5D-3L
inde
x*↑
McG
illpain
questio
nnaire*↓
Trigge
rpo
intsin
thepo
sterior
N/A
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 5 of 21
Table
2Med
icalem
piricalresearch
(n=25)(Con
tinued)
Autho
rs(year)
Research
design
Participants
Interven
tionmeasures
Con
trol
measures
Measuremen
tsandou
tcom
es
Trialg
roup
Con
trol
grou
pSelf-repo
rtmeasures
Physiologicalm
easures
neck
region
# ↓
Ochiai
(2015a)
[22]
NRC
T(before-afterstud
y)※
Maleparticipantswith
high
norm
albloo
dpressure,age
rang
e40–
72years(n
=9)
N/A
Ontriald
ay,p
articipants
wereexpo
sedto
forest
environm
entforactivities
andrestfro
m10:30to
15:05
1)Thetrialw
ascarriedou
tin
early
autumn,andthe
averageairtempe
rature
was
21.5°C.2)N
oalcoho
lor
conversatio
nwas
allowed
durin
gthetrial,andcell
phon
eswereallowed
only
durin
gbreaks
SDmetho
d:Com
fortable
feeling↑
Naturalfeeling*↑
Relaxedfeeling*↑
POMS:
D↓
V↓ T-A*↓
F↓ C*↓
A-H*↓
POMStotal
moo
ddisturbance*↓
SBP*↓
DBP*↓
Urin
aryadrenalinelevels
*↓ Serum
cortisol
levels*↓
Ochiai
(2015b
)[23]
NRC
T(before-afterstud
y)※
Femaleparticipants,the
averageagewas
62.2years
(n=17)
N/A
Ontriald
ay,p
articipants
wereexpo
sedto
forest
environm
entforactivities
andrestfro
m10:32to
15:13
1)Thetrialw
ascarriedou
tin
summer,and
theaverage
airtempe
rature
was
21.5°C.
2)Except
for6participants
who
weretaking
med
icationto
controlthe
irbloo
dpressure,the
restof
theparticipantshadno
othe
rph
ysicalor
psycho
logicald
iseases.3)
Noalcoho
lorcellph
ones
wereallowed
durin
gthe
trial
SDmetho
d:Com
fortable
feeling*↑
Naturalfeeling*↑
Relaxedfeeling*↑
POMS:
T-A*↓
F↓ V*↑
Pulserate*↓
Salivarycortisol
concen
tration*↓
Song
(2015a)
[24]
RCT
(cross-overstud
y)※
Maleparticipants,the
averageagewas
21.5
years(n
=6)
Maleparticipants,
theaverageage
was
21.5years(n=
6)
Day
1,thetrialg
roup
was
expo
sedto
forest
environm
entandwalked
for15
min,w
hilethe
controlg
roup
was
expo
sedto
urban
environm
entandwalked
for15
min.D
ay2,thetw
ogrou
psinterchang
eden
vironm
ents
1)Thetriallastedfor2days.
2)Sm
okinganddrinking
are
proh
ibiteddu
ringthetrial.
3)Thetrialw
ascond
ucted
severaltim
esandatotalo
f92
participantsparticipated
N/A
Iftheparticipantshadhigh
initialbloo
dpressure
and
pulse,forestwalking
could
redu
cethesetw
oindicators.The
results
were
reversed
iftheparticipants
hadlower
initialbloo
dpressure
andpu
lse
Song
(2015b
)[25]
RCT
(cross-overstud
y)※
Maleparticipantswith
hype
rten
sion
orhigh
norm
albloo
dpressure,
theaverageagewas
58years(n
=10)
Maleparticipants
with
hype
rten
sion
orhigh
norm
albloo
dpressure,
theaverageage
was
58years(n=
10)
Day
1,thetrialg
roup
was
expo
sedto
forest
environm
entandwalked
for17
min,w
hilethe
controlg
roup
was
expo
sedto
urban
environm
entandwalked
for17
min.D
ay2,thetw
ogrou
psinterchang
ed
1)Thetriallastedfor2days.
2)Whe
nthetrialw
ascarriedou
t,theaverageair
tempe
rature
intheforest
was
21.4°C,and
that
inthe
city
was
28.1°C.3)Sm
oking,
alcoho
land
caffeine
consum
ptionwere
proh
ibiteddu
ringthetrial.
SDmetho
d:Com
fortablefeeling#↑
Naturalfeeling#↑
Relaxedfeeling#↑
POMS:
D# ↓
V#↑
T-A# ↓
F#↓
lnHF
# ↑Pu
lserate
# ↓
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 6 of 21
Table
2Med
icalem
piricalresearch
(n=25)(Con
tinued)
Autho
rs(year)
Research
design
Participants
Interven
tionmeasures
Con
trol
measures
Measuremen
tsandou
tcom
es
Trialg
roup
Con
trol
grou
pSelf-repo
rtmeasures
Physiologicalm
easures
environm
ents
4)Participantswho
wereon
med
icationwereexclud
ed.
5)Trialatthesametim
eeveryday
C# ↓
A-H
# ↓
Im (2016)
[26]
RCT
(cross-overstud
y)※+
Maleandfemale
participants,age
rang
e18–35years(n
=19)
Maleandfemale
participants,the
agerang
e18–35
years(n=22)
Inthemorning
,the
trial
grou
pwas
expo
sedto
foresten
vironm
entfor2h,
whilethecontrolg
roup
was
expo
sedto
urban
environm
entfor2h.In
the
afternoo
n,thetw
ogrou
psinterchang
eden
vironm
ents
1)Thetrialb
egan
inthe
summer.2)T
heparticipants
hadno
men
talillness,allergic
rhinitisor
bron
chitis.3)
Bachelor’sde
gree
orabove
andlivein
city.4)To
avoid
carryovereffect,the
interval
betw
eenmorning
trialand
afternoo
ntrialw
as2h.
5)Alcoh
olconsum
ptionwas
restricted12
hbe
fore
the
test,and
food
consum
ption
was
restricted1hbe
fore
the
test.Smokinganddrinking
wereproh
ibiteddu
ringthe
test,and
electron
icprod
ucts
wererestricted.
6)Allgrou
pshadthesame
diet
Stress
respon
seinventory:
Total# ↓
Somatic
symptom
s#↓
Dep
ressives
ymptom
s#↓
Ang
ersymptom
s↓
IL-6↑
IL-8
# ↓TN
F-α#↓
GPx
# ↑
Jia (2016)
[27]
RCT※
Maleandfemale
participantswith
COPD
(n=10)
Maleandfemale
participantswith
COPD
(n=8)
Inthemorning
,the
trial
grou
pwas
expo
sedto
foresten
vironm
entand
walkedfor90
min,w
hile
thecontrolg
roup
was
expo
sedto
urban
environm
entandwalked
for90
min.A
fterno
onis
thesameas
morning
1)Thetrialb
egan
inthe
summer.2)T
heparticipants
didno
thave
acute
exacerbatio
n.3)
Participants
have
thesame
accommod
ationand
sche
dule.4)T
hetriallasted
for4days
POMS:
D*↓
V↑ T-A*#↓
F↓ C↓
A-H*↓
NKcells
*↓CD8+
T-lymph
ocytes
expressing
perfo
rin*#↓
NKT-like
cells
*#↓
IL-6*#↓
IL-8*#↓
Interfe
ron-γ*
# ↓TN
F-α↓
IL-1β#↓
CRP
# ↓Pu
lmon
aryandactivation-
regu
latedchem
okine*
# ↓Tissue
inhibitorof
metalloproteinase-1*#↓
SurfactantproteinD
# ↓Cortisol# ↓
Epinep
hrine*
# ↓
Li (2016)
[28]
NRC
T※Maleparticipantswith
hype
rten
sion
orhigh
norm
albloo
dpressure,
agerang
e40–69years
(n=19)
Maleparticipants
with
hype
rten
sion
orhigh
norm
albloo
dpressure,
agerang
e40–69
years(n
=19)
Inthefirsttrial,thecontrol
grou
pwas
expo
sedto
urbanen
vironm
entand
walked2.6km
.Inthe
second
trial,thecontrol
grou
pwas
expo
sedto
foresten
vironm
entand
1)Thetrialb
egan
inthe
summer.2)P
articipantsdid
nottake
any
antih
ypertensivedrug
s.3)
Noalcoho
lwas
allowed
and
thediet
was
thesame
durin
gthetrial.4)
The
POMS:
D# ↓
V#↑
T-A# ↓
F#↓
C# ↓
A-H!
SBP!
DBP!
Pulserate
# ↓Triglycerid
es!
Cho
!LD
L-Cho
!HDL-Cho
!
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 7 of 21
Table
2Med
icalem
piricalresearch
(n=25)(Con
tinued)
Autho
rs(year)
Research
design
Participants
Interven
tionmeasures
Con
trol
measures
Measuremen
tsandou
tcom
es
Trialg
roup
Con
trol
grou
pSelf-repo
rtmeasures
Physiologicalm
easures
walked2.6km
intervalbe
tweenthetw
otrialswas
oneweek
Remnant-like
particlesCho
!Adipo
nectin# ↑
Glycatedhe
mog
lobin!
Bloo
dglucose!
Insulin!
Deh
ydroep
iand
rosteron
esulfate!
CRP!
Epinep
hrine↓
Norep
inep
hrine*#↓
Dop
amine#↓
Bang
(2017)
[29]
NRC
T※Maleandfemale
participants,the
average
agewas
24.8years
(n=51)
Maleandfemale
participants,the
averageagewas
23.8years(n
=48)
Theparticipantswalkedin
thecampu
sforeston
cea
weekfor40
min
1)Thetrialb
egan
inthe
autumn.2)
Thetriallasted
for6weeks.3)Thetrial
grou
preceived
extra
message
sof
encouragem
entdu
ringthe
trialand
attend
edastress
managem
entseminar
Health
-promoting
Lifestyleprofile
II:Total# ↑
Respon
sibilityfor
health
# ↑Ph
ysicalactivity↑
Health
ynu
trition
↑Socialrelatio
ns↑
Stress
managem
ent#↑
Spiritualgrow
th↑
BDIscore
# ↓
SBP#↑
DBP↑
Cho
↓HDL-Cho
↓LD
L-Cho
↑Triglycerid
es# ↓
Bone
density
# ↑Bo
dyMassInde
x↑Percen
tof
body
fat↑
lnLF/ln
HF↑
Parasympatheticne
rve
activity↑
Chu
n(2017)
[30]
RCT※
+Maleandfemale
participantswith
chronic
stroke,the
averageage
was
60.8years(n
=30)
Maleandfemale
participantswith
chronicstroke,the
averageagewas
60.8years(n
=29)
Thetrialg
roup
was
expo
sedto
forest
environm
entfor
med
itatio
nandwalking
.Thecontrolg
roup
was
expo
sedto
urban
environm
entfor
med
itatin
gandwalking
2)Thetriallastedfor4days
BDIscore*#↓
Scoreof
17-item
versionof
the
Ham
ilton
Dep
ression
Ratin
gScale*
# ↓STAIscore*#↓
Reactiveoxygen
metabolites↓
Biolog
icalantio
xidant
potential*# ↑
Kobayashi
(2017)
[31]
RCT
(cross-overstud
y)※
Maleparticipants,the
averageagewas
21.7
years(n
=12)
Maleparticipants,
theaverageage
was
21.7years(n
=12)
Day
1,thetrialg
roup
was
expo
sedto
forest
environm
ent,whilethe
controlg
roup
was
expo
sedto
urban
environm
ent.Day
2,the
twogrou
psinterchang
eden
vironm
ents
1)Thetrialb
egan
inthe
summer
andearly
autumn.
2)Thetriallastedfor2days.
3)34
forestsandcitieswere
selected
forthetrial,anda
totalo
f34
trialswerecarried
out
N/A
Salivarycortisol
concen
tration#↓
Mao (2017)
[32]
RCT※
Maleandfemale
participantswith
chronic
heartfailure,age
rang
e65–80years(n
=23)
Maleandfemale
participantswith
chroniche
art
failure,age
rang
e65–80years(n
=10)
Thetrialg
roup
and
controlg
roup
were
expo
sedto
forestand
urbanen
vironm
ent,
respectively,andwalked
for1.5hin
themorning
andafternoo
n
1)Thetrialb
egan
inthe
summer.2)T
hetriallasted
for5days.3)Allgrou
pshad
thesamediet.4)S
moking,
drinking
alcoho
land
caffeinated
beverage
swere
proh
ibiteddu
ringthetrial.
5)Med
icationtaken
POMS:
D*#↓
V↓ T-A# ↓
F↓ C*↓
A-H*↓
BNP*
# ↓N-terminalpro-BN
P!Endo
thelin-1
# ↓ANGII↓
ANGIIreceptor
type
1↑ANGIIreceptor
type
2*↑
Ang
iotensinog
en↓
IL-6
# ↓
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 8 of 21
Table
2Med
icalem
piricalresearch
(n=25)(Con
tinued)
Autho
rs(year)
Research
design
Participants
Interven
tionmeasures
Con
trol
measures
Measuremen
tsandou
tcom
es
Trialg
roup
Con
trol
grou
pSelf-repo
rtmeasures
Physiologicalm
easures
norm
allydu
ringthetrial
TNF-α↓
CRP↓
Totalsup
eroxide
dism
utase#↑
Malon
dialde
hyde
# ↓
Yu (2017)
[33]
NRC
T(before-afterstud
y)※
Maleandfemale
participants,age
rang
e45–86years(n
=128)
N/A
participantswererecruited
atthegate
oftheforest
park
tocond
ucta2-h
foresttour
andwalka
totalo
f2.5km
1)Thetrialb
egan
inthe
summer.2)S
moking,
drinking
alcoho
land
caffeinated
beverage
swere
proh
ibiteddu
ringthetrial
POMS:
D*↓
V*↑
T-A*↓
F*↓
C*↓
A-H*↓
STAIscore*↓
Pulserate
*↓SBP*↓
DBP*↓
lnHF↓
lnLF/ln
HF↑
Bang
(2018)
[34]
NRC
T(before-afterstud
y)※
Elem
entary
scho
olstud
ents,the
average
agewas
11.83years
(n=24)
Elem
entary
scho
olstud
ents,the
averageagewas
11.75years(n
=28)
Thetrialg
roup
allocated
30min
forthelectureand
60min
fortheforest
activities,w
hilethecontrol
grou
ptook
onlyindo
orclasses
1)Thetrialb
egan
inthe
summer.2)O
nceaweekfor
10weeks.3)C
hildrenwith
med
icaltreatm
entand
contraindicatio
nsto
exercise
wereexclud
ed
1)Trialg
roup
Health
status
questio
nnaire:
Perceivedhe
alth
status↑
Rosenb
ergSelf-
Esteem
Scale:
Self-esteem
*↑Children’s
Dep
ressionInventory:
D*↓
Peer
relatio
nship
instrumen
t:Peer
relatio
nships↓
Con
ners-W
ells
Ado
lescen
tsSelf-
Repo
rtScales:
Atten
tionde
ficit
andhype
ractivity↑
2)Con
trol
grou
pHealth
status
questio
nnaire:
Perceivedhe
alth
status↑
Rosenb
ergSelf-
Esteem
Scale:
Self-esteem
↓Children’sDep
ression
Inventory:
D↓
Peer
relatio
nship
instrumen
t:Peer
relatio
nships↑
Con
ners–W
ells
1)Trialg
roup
lnLF/ln
HF↑
2)Con
trol
grou
plnLF/ln
HF↓
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 9 of 21
Table
2Med
icalem
piricalresearch
(n=25)(Con
tinued)
Autho
rs(year)
Research
design
Participants
Interven
tionmeasures
Con
trol
measures
Measuremen
tsandou
tcom
es
Trialg
roup
Con
trol
grou
pSelf-repo
rtmeasures
Physiologicalm
easures
Ado
lescen
tsSelf-Repo
rtScales:
Atten
tionde
ficit
andhype
ractivity↓
Bielinis
(2018)
[35]
RCT※
Male(n
=18)and
female(n
=13)
participants,the
average
agewas
21.45years
Male(n
=18)and
female(n
=13)
participants,the
averageagewas
21.45years
Thetrialg
roup
was
expo
sedto
theforest
environm
ent(deciduo
usbroad-leaved
forest)and
watched
thescen
eryfor
15min,w
hilethecontrol
grou
pwas
expo
sedto
the
urbanen
vironm
entand
watched
thescen
eryfor
15min
1)Thetrialb
egan
inthe
winter.2)
Notalkingwith
each
othe
rdu
ringthetrial
Positiveand
negativeaffect
sche
dule:
Positive*
# ↑Neg
ative#↓
POMS:
D# ↓
V*# ↑
T-A# ↓
F*# ↓
C# ↓
A-H
# ↓Restorative
OutcomeScale
scores*#↑
SubjectiveVitality
Scalescores*#↑
N/A
Che
n(2018)
[36]
NRC
T(before-afterstud
y)※
Femaleparticipants,age
rang
e36–62years
(n=16)
N/A
Day
1,participantswere
expo
sedto
forest
environm
entsforwalking
.Day
2,participantswere
expo
sedto
forest
environm
entsandmade
hand
icrafts
1)Theaverageair
tempe
rature
durin
gthetrial
was
13.8°C.2)participants
hadthesame
accommod
ationanddiet.3)
Smokingandstim
ulant
food
swereproh
ibited
durin
gthetrial
POMS:
D↓
V*↑
T-A*↓
F*↓
C*↓
A-H*↓
STAIscores*↓
Pulserate↓
SBP*↓
DBP↓
Salivaryα-am
ylase↓
Hassan
(2018)
[37]
RCT
(cross-overstud
y)※
Maleandfemale
participants,age
rang
e19–24years(n
=30)
Maleandfemale
participants,age
rang
e19–24years
(n=30)
Day
1,thetrialg
roup
was
expo
sedto
forest
environm
entandwalked
for15
min,w
hilethe
controlg
roup
was
expo
sedto
urban
environm
entandwalked
for15
min.D
ay2,thetw
ogrou
psinterchang
eden
vironm
ents
1)Theaverageair
tempe
rature
onthefirstday
was
22°C,and
theaverage
airtempe
rature
onthe
second
daywas
27°C.2)
Thetriallastedfor2days.3)
Participantshadthesame
accommod
ationanddiet
STAIscores#↓
SDmetho
d:Com
fortablefeeling#↑
Naturalfeeling#↑
Relaxedfeeling#↑
SBP#↓
DBP
# ↓Highalph
abrainwaves
# ↑Highbe
tabrainwaves
# ↑Relaxatio
nscores
# ↑Atten
tionscores
# ↑
Kobayashi
(2018)
[38]
RCT
(cross-overstud
y)※
Maleandfemale
participants,age
rang
e19–29years(n
=N/A)
Maleandfemale
participants,age
rang
e19–29years
(n=N/A)
Day
1,thetrialg
roup
was
expo
sedto
forest
environm
entandwalked
for15
min,w
hilethe
controlg
roup
was
expo
sedto
urban
environm
entandwalked
for15
min.D
ay2,thetw
o
1)Thetrialw
ascarriedou
tin
57citiesandforestareas.
2)Thetriallastedfor2days.
3)Thetotaln
umbe
rof
participantswas
684,and
thenu
mbe
rsof
participants
from
trialg
roup
orcontrol
grou
pweredifferent
inevery
N/A
lnHF#↑
lnLF/ln
HF
# ↓
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 10 of 21
Table
2Med
icalem
piricalresearch
(n=25)(Con
tinued)
Autho
rs(year)
Research
design
Participants
Interven
tionmeasures
Con
trol
measures
Measuremen
tsandou
tcom
es
Trialg
roup
Con
trol
grou
pSelf-repo
rtmeasures
Physiologicalm
easures
grou
psinterchang
eden
vironm
ents
trial
Mao (2018)
[39]
RCT※
Firsttrial,maleand
femaleparticipantswith
chroniche
artfailure
(n=23).
Second
trial,maleand
femaleparticipantswith
chroniche
artfailure
(n=10)
Maleandfemale
participantswith
chroniche
art
failure
(n=10)
Thetrialg
roup
was
expo
sedto
forest
environm
ent,while
thecontrolg
roup
was
expo
sedto
urban
environm
ent
1)Thetrialw
ascarriedou
ttw
ice,thefirsttim
ein
late
summer
for5days,and
the
second
timein
early
autumn
for5days.2)Noalcoho
lor
teawas
allowed
durin
gthe
trial
N/A
BNP*
# ↓IL-6!
TNF-α*
# ↓Totalsup
eroxide
dism
utase!
Malon
dialde
hyde
# ↓SBP↓
DBP↓
Song
(2018)
[40]
RCT
(cross-overstud
y)※
Maleparticipants,
averageagewas
21.7
years(n
=6)
Maleparticipants,
theaverageage
was
21.7years(n
=6)
Day
1,thetrialg
roup
was
expo
sedto
forest
environm
ent,whilethe
controlg
roup
was
expo
sedto
urban
environm
ent.Day
2,thetw
ogrou
psinterchang
eden
vironm
ents
1)Thetrialw
ascond
ucted
inthesummer
from
2005
to2013
andlasted
for2days
atatim
e.2)
Thestud
ywas
cond
uctedin
52urbanand
forestareaswith
atotalo
f585participants.3)S
moking
anddrinking
alcoho
lwere
proh
ibited,
andlim
ited
caffeineintake
POMS:
D# ↓
V#↑
T-A# ↓
F#↓
C# ↓
A-H
# ↓
N/A
Tsao
(2018)
[41]
NRC
T(before-afterstud
y)※
Maleandfemale
participants,the
average
agewas
60.4years
(n=11)
N/A
Participantswereexpo
sed
toforesten
vironm
entand
walked1.5hin
the
morning
andafternoo
n(in
twodifferent
forests)
1)Thetrialb
egan
inthe
winter.2)
Thetriallastedfor
5days.3)T
heparticipants
hadno
diabetes,
cardiovascular
diseaseor
othe
rmajor
diseases.4)D
iet
controlb
egan
10days
before
thetrial
N/A
NKcells↑
NKcells
activity*↑
Wang
(2018)
[42]
NRC
T(before-afterstud
y)※
Maleandfemalecollege
stud
ents(n
=22)
N/A
Theparticipantscarried
outa2to
3-dayforesttrip
1)Thetrialw
ascond
ucted
inthefallof
2015,2016and
2017.2)P
articipantshadthe
samediet.3)S
moking,
coffeeandteawereno
tallowed
durin
gthetrial
N/A
1)Day
afterthetrial:
Urin
aryhydrog
enpe
roxide
*↓Urin
ary8-hydroxy-
2’de
oxyguano
sine
*↓2)
One
weekafterthetest:
Urin
aryhydrog
enpe
roxide
*↓Urin
ary↓
8-hydroxy-
2’de
oxyguano
sine
*↓
Song
(2019)
[43]
RCT
(cross-overstud
y)※
Femaleparticipants,the
averageagewas
21years(n
=6)
Female
participants,the
averageagewas
21years(n
=6)
Theparticipantswalkedin
urbanor
forest
environm
entfor15
min
(abo
ut1km
)
1)Thetrialw
ascond
ucted
inlate
summer
andearly
autumnof
2014,2015and
2017.2)T
hetrialw
ascond
uctedin
6different
urbanandforest
environm
entswith
atotalo
f
POMS:
D# ↓
V#↑
T-A# ↓
F#↓
C# ↓
A-H
# ↓
lnHF#↑
lnLF/ln
HF#↓
Heartrate
# ↓
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 11 of 21
Table
2Med
icalem
piricalresearch
(n=25)(Con
tinued)
Autho
rs(year)
Research
design
Participants
Interven
tionmeasures
Con
trol
measures
Measuremen
tsandou
tcom
es
Trialg
roup
Con
trol
grou
pSelf-repo
rtmeasures
Physiologicalm
easures
72participants.3)S
moking,
drinking
alcoho
lwas
proh
ibited,
andlim
ited
caffeineintake
SDmetho
d:Com
fortablefeeling#↑
Naturalfeeling#↑
Relaxedfeeling#↑
*Significan
tintra-grou
pdifferen
ces
# Significan
tinter-grou
pdifferen
ces
n,samplesize;“↑”,ind
icatorsrise;
“↓”,indicators
decline;
“!”,irreg
ular
inde
x;N/A,n
orepo
rt;“※”,ha
spa
ssed
ethicalreview;“+”,illustrates
thegrou
ping
metho
d;ANGII,Ang
iotensin
II;A-H,ang
eran
dho
stility;B
DI,Be
ckde
pression
inventory;BN
P,Brainna
triuretic
peptide;
C,confusion;
Cho,
totalcho
lesterol;C
OPD
,chron
icob
structivepu
lmon
arydisease;
CRP,
C-reactiveprotein;
D,d
epression;
DBP
,diastolicbloo
dpressure;F,fatigue
;HRV
,heartrate
varia
bility;HDL,Highde
nsity
lipop
rotein;IL,Interle
ukin;LDL,low
density
lipop
rotein;lnH
F,thena
turallog
arith
micvalueof
thehigh
freq
uencyof
heartrate
varia
bility;lnLF,the
naturallog
arith
micvalue
ofthelow
freq
uencyof
heartrate
varia
bility;NK,
Naturekiller;NKT,N
aturekillerT;NRC
T,no
n-rand
omized
controlledtrial;PO
MS,profile
ofmoo
dstates;R
CT,ran
domized
controlledtrial;SBP,
systolicbloo
dpressure;SD,
seman
ticdifferen
tial;STAI,state-traitan
xietyinventory;T-A,ten
sion
andan
xiety;TN
F-α,
tumor
necrosisfactor-α;V
,vigor;V
AS,visual
analog
scale
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 12 of 21
Table
3Interdisciplinaryresearch
(n=3)
Autho
rs(year)
Research
design
Participants
Interven
tion
measures
Con
trol
measures
Measuremen
tsOutcomes
Trialg
roup
Con
trol
grou
pSelf-repo
rtmeasures
Physiological
measures
Forestinventory
Takayama
(2017)
[44]
NRC
T(cross-overstud
y)※
1)Maleand
female
participants,
theaverage
agewas
40.2years
(n=9).
2)Sparse
forest
environm
ent
1)Maleand
female
participants,
theaverage
agewas
40.2years
(n=9).2)
Den
seforest
environm
ent
Thetrialg
roup
was
expo
sed
toasparse
forest
environm
ent
andsatqu
ietly
for15
min,
whilethe
controlg
roup
was
expo
sed
toade
nse
forest
environm
ent
andsatqu
ietly
for15
min,and
then
thetw
ogrou
psexchange
den
vironm
ents
1)Thetrial
beganin
the
summer.2)The
triallastedfor
4days.3)
Alcoh
olwas
bann
ed24
hbe
fore
thetrial
andcaffeine
was
bann
ed12
hbe
fore
the
trial.4)
All
subjectsdid
nothave
ahistoryof
cardiovascular
diseaseand
psycho
sis,and
didno
ttake
med
ications
that
could
affect
their
psycho
logy.5)
Theinterval
betw
eenthe
trialindifferent
environm
ents
was
10min
Positiveand
Neg
ativeAffect
Sche
dule:
Positive↑
Neg
ative*↓
POMS:
D# *↓
V↑ T-A↓
F↓ C↓
A-H↓
Perceived
Restorativen
ess
Scale:
Com
patib
ility
scores
# ↑Restorative
OutcomeScale
scores↑
N/A
Standde
nsity
Standbasalarea
Species
compo
sitio
nForestph
otos
Hem
isph
erical
photog
raph
Forest
micrometeo
rology
Tempe
rature↑
Relative
humidity
# ↑Wind
velocity# ↓
Radianthe
at↑
Illum
inance
# ↑Soun
dpressure
# ↑
1)Bo
thsparse
forestandde
nse
foresthad
recovery
effect
ontheparticipants,
butthe
participants
evaluatedthe
sparse
forest
environm
ent
morepo
sitively.2)
Streng
then
ing
foreststructure
managem
entcan
improvethe
healingeffect
offorest
environm
enton
human
body
Guan
(2017)
[45]
RCT
1)Maleandfemale
participants,the
average
agewas
22years(n
=20).
Theen
vironm
entisbirch
forest(Betulaplatyph
ylla
Suk).
2)Maleandfemale
participants,the
averageagewas
21.6years(n
=23).
Theen
vironm
entis
mapleforest
(Acertriflorum
)3)
Maleandfemale
participants,the
averageagewas
21.6years(n
=26).
Theen
vironm
entis
oakforest
The
participants
wereexpo
sed
totheforest
environm
ent,
firsttaking
atree-m
easurin
gcourse
for
20min,and
then
enjoying
40min
ofprivatetim
e
1)Thetrial
beganin
the
sprin
g.2)
All
participants
hadno
history
of cardiovascular
disease,allergic
symptom
s,or
men
talillness.
3)High-
intensity
activ
ities,smoking
anddrinking
wereproh
ibiteddu
ringthe
trial
Hom
emade
scales:
Anxiety
caused
byem
ploymen
tpressure
(birch
forest)*↓
Anxiety
caused
bystud
yinterest
(mapleforest)*↓
Anxiety
caused
bylesion
satisfaction
(oak
forest)#↓
N/A
Heigh
tof
tree
Diameter
atbreasthe
ight
Canop
yleng
thCanop
ycover
rate
Den
sity
1)Thecorrelationof
weigh
t,age
andanti-anxietyscorewas
thehigh
est.
2)Forestbathingcan
prom
otecollege
stud
ents'inter
estin
learning
.3)O
verw
eigh
tyoun
gpe
oplewerebe
tter
atre
ducing
anxiety.4)
Femalepartici
pantsin
theoakforestshow
edhigh
erlevelsof
anxietyreliefthan
male
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 13 of 21
Table
3Interdisciplinaryresearch
(n=3)
(Con
tinued)
Autho
rs(year)
Research
design
Participants
Interven
tion
measures
Con
trol
measures
Measuremen
tsOutcomes
Trialg
roup
Con
trol
grou
pSelf-repo
rtmeasures
Physiological
measures
Forestinventory
(Quercus
mon
golica)
Zhou
(2019)
[46]
RCT
(cross-overstud
y)Maleand
female
participants,
agerang
e19–23years
(n=24)
Maleandfemale
participants,age
rang
e19–23years
(n=19)
Day
1,thetrial
grou
pwas
expo
sedto
urbanforest
park,w
hilethe
controlg
roup
was
expo
sed
tosubu
rban
forestparks.
Day
2,thetw
ogrou
psinterchang
eden
vironm
ents
1)Thetrial
beganin
the
winter.2)
The
triallastedfor
2days
Hom
emade
scales
(anti-anxiety
score):
Financestate*↑
Exam
-pass
pressure*#↓
Cam
puslife*
# ↓Love
affair
relatio
nship*↑
N/A
Canop
yde
nsity
Diameter
atbreasthe
ight
Plantspecies
1)Theforestrichn
essof
subu
rban
forestpark
ishigh
erthan
that
ofurbanforestpark.2)Subu
rban
forestpark
canalleviate
interpersonalanxiety
inparticipantsmorethan
urban
forestparks
*Significan
tintra-grou
pdifferen
ces
# Significan
tinter-grou
pdifferen
ces
n,samplesize;“↑”,ind
icatorsrise;
“↓”,Indicators
decline;
N/A,n
orepo
rt;“※”,ha
spa
ssed
ethicalreview;A
-H,ang
eran
dho
stility;C
,con
fusion
;D,d
epression;
F,fatig
ue;N
RCT,no
n-rand
omized
controlledtrial;PO
MS,
profile
ofmoo
dstates;R
CT,ran
domized
controlledtrial;T-A,ten
sion
andan
xiety;V,
vigo
r
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 14 of 21
Interleukin (IL)-6, which was significantly decreased in 2studies [27, 32]. There were 2 studies [26, 27] involvingIL-8, which was significantly decreased. There were 3studies [26, 32, 39] involving tumor necrosis factor-alpha, which was significantly decreased in 2 studies [26,39]. There were 3 studies [27, 28, 32] involving C-reactive protein, which was significantly decreased in 1study [27]. There was 1 study [27] involving IL-1β,Interferon-γ, pulmonary and activation-regulated che-mokine, tissue inhibitor of metalloproteinase-1 and sur-factant protein D, which were all significantly decreased.
Antioxidant indexesThere was 1 study [26] involving glutathione peroxidase,which was significantly increased. There was 1 study[30] involving biological antioxidant potential, whichwas significantly increased. There was 1 study [42] in-volving 8-hydroxy-2′deoxyguanosine and hydrogen per-oxide, which were significantly decreased. There were 2studies [32, 39] involving total superoxide dismutase,which was significantly increased in 1 study [32]. Therewere 2 studies [32, 39] involving malondialdehyde, whichwas significantly decreased.
Electrophysiological indexesThere was 1 study [37] involving electroencephalogram,high alpha brain waves and high beta brain waves, whichwere significantly increased, and the degree of relaxationof the human body was significantly increased.
Psychological outcomesEmotional statesThere were 14 studies [19, 20, 22, 23, 25, 27, 28, 32, 33,35, 36, 40, 43, 44] involving the emotional states ofhumans. Among them, “depression,” “tension-anxiety,”“fatigue,” “confusion,” and “anger-hostility” scores weresignificantly decreased in 11 studies [19, 20, 25, 27, 28,32, 33, 35, 40, 43, 44], 13 studies [19, 20, 22, 23, 25, 27,28, 32, 33, 35, 36, 40, 43], 9 studies [19, 20, 25, 28, 33,35, 36, 40, 43], 11 studies [19, 20, 22, 25, 28, 32, 33, 35,36, 40, 43], and 11 studies [19, 20, 22, 25, 27, 32, 33, 35,36, 40, 43] respectively. There were 10 studies [19, 20,23, 25, 28, 33, 35, 36, 40, 43] in which the “vigor” scorewas significantly increased. In addition, 2 studies [35, 44]showed that forest bathing significantly increased posi-tive emotions and decreased negative emotions.
Attitudes and feelings towards thingsThere were 6 studies [20, 22, 23, 25, 37, 43] involvingpeople’s attitudes and feelings towards things; “comfort-able,” “relaxed,” and “natural” scores were significantlyincreased in 5 studies [20, 23, 25, 37, 43], 6 studies [20,22, 23, 25, 37, 43], and 6 studies [20, 22, 23, 25, 37, 43],respectively.
Levels of anxiety and depressionThere were 6 studies [30, 33, 36, 37, 45, 46] in whichlevels of anxiety were significantly decreased. There were3 studies [29, 30, 34] in which levels of depression weresignificantly decreased.
Degree of physical and psychological recoveryThere were 2 studies [21, 26] involving the degree ofphysical recovery, in which somatic symptoms were sig-nificantly decreased. There were 2 studies [35, 44] inwhich the degree of psychological recovery and mentalhealth were significantly increased.
Adaptive behaviorThere were 2 studies [29, 34] involving adaptive behavior,and the “self-esteem” score was significantly increased in 1study [34], and the “health promoting behavior” score wassignificantly increased in 1 study [29].
Comprehensive studyThe study of the comprehensive health care effect offorest bathing on the human body is still at the primarystage, and the health care mechanism has not been fullyproved. It is general practice to assume that forest bath-ing has positive effects on the physical or psychologicalhealth of a certain group of people (such as cardiovascu-lar disease patients, chronic obstructive pulmonarydisease patients, the subhealth population, etc.) and toverify whether this hypothesis is valid. The autonomicnervous system that plays a mediating role in the stressresponse of various systems has attracted the attentionof researchers. Based on the data of the 28 papersincluded in this study, the lnHF of HRV can reflectparasympathetic activity, and the lnLF/lnHF of HRV,urinary adrenalin and norepinephrine can reflectsympathetic activity [22, 38]. When participants were ex-posed to walking in the forest environment, the cerebralcortex was in a relaxed state, parasympathetic activityincreased (lnHF increased), and sympathetic activitydecreased (lnLF/lnHF, urinary adrenalin and norepin-ephrine decreased) [20, 25]. Cardiovascular function andhemodynamic index, neuroendocrine index, metabolismindex, immune and inflammatory index, antioxidationindex, and electrical physiological indexes of the humanbody, emotional state, attitudes and feelings towardsthings, physiological and psychological recovery degree,and adaptive behavior of the human body were signifi-cantly improved. Levels of anxiety and depression weresignificantly decreased. Song et al. [24] found that highinitial values in parameters such as blood pressure andpulse rate in participants were decreased after walking inthe forest environment, while participants with lowerinitial values had the opposite effect. Participants whowalked in urban environments did not experience this
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 15 of 21
phenomenon. This indicates that the physiological effectwill vary depending on the initial value of the partici-pant, and the forest has a physiological regulation effectclose to the appropriate level of the human body, whichis not completely caused by the exercise itself. Horiuchiet al. [19] also indicated that the healing effect of forestbathing has nothing to do with the energy expenditureduring walking. The health benefits of forest bathing areshown in Fig. 2.
Quality assessmentFor methodological quality assessment of papers basedon the Downs and Black checklist, of the 28 papers in-cluded in the study, 16 [21, 24, 26, 27, 29–32, 34, 35, 38,39, 41, 44–46] were of high quality and 12 [19, 20, 22,23, 25, 28, 33, 36, 37, 40, 42, 43] were of low quality(Fig. 3). Among the 16 high-quality papers, there were12 [21, 24, 26, 27, 30–32, 35, 38, 39, 45, 46] with RCTand 4 [29, 34, 41, 44] with NRCT. The methodologicalquality of papers using RCT is significantly higher thanthat of papers using NRCT (p < 0.05) (Fig. 4). On thewhole, the quality of papers designed with RCT washigher than those with NRCT. In terms of the gener-ation of random sequences, only 1 paper [30] usedcomputer-generated random codes with a low risk ofbias. None of the following was mentioned or carried
out in the papers: (1) return visit; (2) blind method forintervention practitioners, participants, or data analysts;(3) explain the compliance with the intervention or con-trol measures; and (4) participants who were lost tofollow-up were included in the study or carried out theintention-to-treat analysis.
DiscussionStudies on the health effects of forest environment ex-posure on the human body are gradually increasing.Currently, there are two main mainstream models. Oneis the forest bathing model, which advocates subhealthypeople and sick people going into the forest for activitieswhich generate a healing effect through forest environ-mental factors. Forest bathing can regulate blood pres-sure, reduce blood glucose, regulate endocrine activity,relieve mental disorders, fight cancer, boost immunity,and treat respiratory diseases [3, 47–52]. In recent years,increasing numbers of forest bathing trial studies havebeen conducted on people with chronic diseases, such aspatients with hypertension or high-normal blood pres-sure [22, 25, 28, 30, 53], chronic obstructive pulmonarydisease patients [27], chronic heart failure [32, 39], andchronic stroke [30]. The second is horticultural therapy,which guides sick people into the natural environmentand relieves diseases caused mainly by mental stress
Fig. 2 Health benefits of forest bathing
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 16 of 21
(excessive tension, panic, insomnia, etc.) through com-munication with people, making crafts, and gardeningactivities. Others include pain and sports injuries such asmild hemiplegia, lower body paralysis, and cognitive im-pairments such as speech disorders, spatial identificationdisorders, memory disorders, attention disorders, andillogicality [54, 55]. The similarities between forest bath-ing and horticultural therapy are as follows: (1) They arecomplementary therapies and cannot replace drugs. (2)
They are a healing method to restore the health of thehuman body through the “five senses experience.” Thedifference between forest bathing and horticultural ther-apy are as follows: (1) Their medical categories aredifferent. Forest bathing belongs to the category of pre-ventive medicine, which is mainly aimed at subhealthypeople, and the prevention of diseases is its main pur-pose. Horticultural therapy belongs to the category of re-habilitation medicine, which is mainly aimed ateliminating and reducing dysfunction of the humanbody, and making up and rebuilding the function of thehuman body is its main purpose. (2) Their core contentis different. The main content of forest bathing is to ex-ercise or meditate in the forest environment, using theforest environmental factors to promote human physicaland psychological health. Horticultural therapy is morefocused on hand-brain coordination, emphasizing con-tact with natural things and gaining satisfaction throughwork. In view of this, different populations shouldchoose appropriate healthcare models. Some scholars[36] combined the 2 healthcare models and achievedvery good results.Based on the data of the 28 papers included in this
study, forest bathing has a significant role in promotinghuman physiology and mental health. Past methodsusing physiological and self-report measures to distin-guish between physiological and psychological researchare no longer feasible. The boundaries between the two
Fig. 3 Quality appraisal of included studies using a Downs and Black checklist
Fig. 4 Score of RCT (n = 17) and NRCT (n = 11), means ± SD, *p <0.05, one-way analysis of variance (ANOVA)
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 17 of 21
are becoming increasingly blurred. The mainstream re-search method in the future will be systematic study ofphysiological measures combined with self-report mea-sures. For example, in the study of the recovery of phys-ical symptoms or the relief of physiological pain, healtheffects can be shown by physiological indicators, butself-report measures (such as visual analog scale [21],stress response inventory [26], etc.) can also be used forevidence. Research on the regulation of the human emo-tional state can use self-reported measures for proof,and physiological measures can also be used for evidence(such as HRV [25, 33, 38], brain wave activity [37], andskin electricity [53]). Although the forest environmenthas obvious effects on the health of the human body andhas achieved certain research results, there are still someproblems: (1) Lack of basic theoretical research andmultidisciplinary communication. At present, most stud-ies are based on qualitative or quantitative analysis ofevidence-based medicine, lacking basic theoretical re-search of forestry. Medical scholars lack guidance fromforestry scholars, relying on subjective or instantaneousforest environmental factor data to determine whether aparticular forest has health benefits and environmentalfactors that lead to increased risk of bias. Forest scholarslack guidance from medical scholars, and the trial partic-ipants are mostly healthy young people, most of whomfail to consider ethical issues and measure physiologicalindicators. Some scholars [45, 46] conduct small samplestudies with homemade scales that fail to pass the reli-ability and validity test, and the evidence is not convin-cing enough. (2) The risk of bias in the papers isrelatively high. Overall, in the 28 papers included in thestudy, the random sequence generation, the allocationconcealment, and the application of blinded methods areimportant sources of bias. Loss to follow-up, reportedadverse events, and intervention-measures or control-measure compliance are the secondary sources of bias.The forest environment is also one of the potentialsources of bias.Interdisciplinary communication between forestry and
medicine is an important measure to reduce the biascaused by environmental factors. The forest environ-ment mainly affects human health through “five sensesexperience,” relying on the synergistic effect between aseries of forest environmental factors (such as phyton-cide, negative air ions, oxygen, and forest microclimate).These environmental factors have significant seasonal,diurnal, and regional variations. The tree speciescomposition and color and forest density are also im-portant influencing factors and can affect human health,especially mental health. Forest environmental factors inindividual studies show that phytoncide with antioxi-dant and antiseptic enhance immunity function [51,56]. Air negative ions have the effect of increasing
parasympathetic activity, relieving depression, andlowering blood glucose [57–59]. The forest microcli-mate can improve human thermal comfort and reduceheat stress [60, 61]. A large area of green in the for-est can bring a sense of security and calm and signifi-cantly reduce anxiety and negative emotions [62].Comprehensive analysis of the forest environment anddynamic monitoring of key environmental factors areimportant to judge the potential health benefits of theforest and reveal the healthcare mechanism of forestbathing. This has important guiding significance forthe formation of industry standards and the establish-ment of a forest bathing base.Reducing the risk of bias is an urgent problem to
be solved in medical empirical research of forestbathing, for example, RCT, a method of random se-quence generation which should be described in de-tail. The study of low bias risk should use randomnumber tables, computer software for random num-ber generation, flipping a coin, rolling dice, shufflingcards, or envelopes, etc., rather than odd and evennumbers, date of birth, subjective assignment, etc. Inforest bathing trials, it is complicated to assign con-cealment and apply a blind method to participantsand personnel. If trial conditions are limited, a cross-over study can be added to reduce the risk of bias,but the length of the washout period should be con-sidered to avoid a carryover effect. Blind methodsshould be applied to data collectors and outcome as-sessors to reduce the risk of bias, as conditions per-mit. Generally, participants are subjectively moreinclined to participate in the forest bathing groupthan the control group. If the guide introduces toomuch information about the healthcare efficacy offorest bathing, this may give the participants psycho-logical hints, which may increase the risk of bias. Dueto the small number of forest bathing test samplesand relatively short trial time, the proportion of par-ticipants lost to follow-up is small. In case of follow-up loss, the risk of bias can be reduced by estimatingthe missing data and conducting intention-to-treatanalysis. Adverse events such as snake bites, pollen al-lergies, falls, and bruises were rarely mentioned in theforest bathing study. Adverse events during the trialshould be explained in the paper. Compliance withintervention or control measures is also rarely men-tioned in forest bathing studies, especially for forestbathing activities greater than one day. Participantcompliance with intervention measures such as walk-ing, making crafts, meditating, and taking classes, aswell as compliance with restrictions or prohibitionson the use of electronic products, communication,caffeine intake, smoking, and drinking, should beexplained.
Wen et al. Environmental Health and Preventive Medicine (2019) 24:70 Page 18 of 21
ConclusionForest bathing activities may significantly improve people’sphysical and psychological health. In terms of medical em-pirical studies on forest bathing, the methodological qualityof RCTs is significantly higher than that of NRCTs. In thefuture, medical empirical studies of forest bathing shouldreinforce basic studies and interdisciplinary exchange to en-hance the methodological quality of papers while decreas-ing the risk of bias, thereby raising the grade of paperevidence.
Appendix
Table 4 Search words (subject word and random word)
Intervention Outcome Combinedterms
1) Forest bathing/ 17) Health care/ 37) 16AND 36
2) Forest natureconvalescent/
18) Healing/
3) Forest therapy/ 19) Therapy/
4) Shinrin-yoku/ 20) Recover/
5) Forest travel/ 21) Vigor/
6) Forest walking/ 22) Spirit/
7) Forest yoga/ 23) Pressure/
8) Forest/ 24) Depression/
9) Forest meditation/ 25) Anxiety/
10) Forest environment/ 26) Brain wave/
11) Forest areas/ 27) Pulse/
12) Phytoncide/ 28) Heart rate/
13) Negative air ions/ 29) Blood pressure/
14) Negative oxygen ions/ 30) Blood glucose/
15) Oxygen/ 31) Saliva/
16) 1 OR 2 OR 3 OR 4 OR 5OR 6 OR 7 OR 8 OR 9 OR 10OR 11 OR 12 OR 13 OR 14
OR 15
32) Inflammatory factor/
33) Immune/
34) Hormonal readiness/
35) Skin conductance/
36) 17 OR 18 OR 19 OR 20OR 21 OR 22 OR 23 OR 24OR 25 OR 26 OR 27 OR 28OR 29 OR 30 OR 31 OR 32
OR 33 OR 34 OR 35
AbbreviationsHRV: Heart rate variability; IL: Interleukin; lnHF: The natural logarithmic valueof the high frequency of heart rate variability; lnLF: The natural logarithmicvalue of the low frequency of heart rate variability; NK: Nature killer;NRCT: Non-randomized controlled trial; RCT: Randomized controlled trial;SBP: Systolic blood pressure
AcknowledgementsNot applicable
Authors’ contributionsYL and XG conceived this study. YW analyzed the data and was a majorcontributor in writing the manuscript. YW, QY, and YP conducted thesystematic review. All authors read and approved the final manuscript.
FundingThis work was supported by funds from the National Natural ScienceFoundation of China (31660230).
Availability of data and materialsNot applicable
Ethics approval and consent to participateNot applicable
Consent for publicationNot applicable
Competing interestsThe authors declare that they have no competing interests.
Author details1College of Forestry, Jiangxi Agricultural University, 1101 ZhiMin Road,Nanchang 330045, China. 2Jiangxi Academy of Forestry, 1629 FengLin Road,Nanchang 330032, China.
Received: 22 July 2019 Accepted: 1 October 2019
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