Medical empirical research on forest bathing (Shinrin-yoku): a ......The theoretical basis of research varies. Medical scholars mainly take evidence-based medicine as the theoretical

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

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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


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)


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


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


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

# ↓


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

!


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.


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

# ↓


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↓


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.


3)Thetotaln

umbe

rof

participantswas

684,and

thenu

mbe

rsof

participants

from

trialg

roup

orcontrol

grou

pweredifferent

inevery

N/A

lnHF#↑

lnLF/ln

HF

# ↓


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

# ↓


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


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


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


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


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


(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)


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.


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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Medical empirical research on forest bathing (Shinrin-yoku): a ......The theoretical basis of research varies. Medical scholars mainly take evidence-based medicine as the theoretical