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A systematic literature review and meta-analysis
of the clinical effects of aroma inhalation therapy
on sleep problems
Moon Joo Cheong, PhD
a
, Sungchul Kim, KMD, PhD
b
, Jee Su Kim
c
, Hyeryun Lee
c
,
Yeoung-Su Lyu, KMD, PhD
a,c
, Yu Ra Lee
a
, Byeonghyeon Jeon, PhD
a
, Hyung Won Kang, KMD, PhD
c,d,∗
Abstract
Background: This systematic review investigated the clinical effects of inhalation aromatherapy for the treatment of sleep
problems such as insomnia.
Methods: Studies on sleep problems and inhalation aromatherapy, published in Korean and international journals, were included in
the meta-analysis. Five domestic and international databases, respectively each, were used for the literature search. Keywords
included sleep disorder, sleep problems, insomnia, and aroma inhalation, and the related literature was further searched. After the
screening, selected articles were assessed for their quality and conducted the risk of bias using RevMan 5.0, a systematic literature
review was then conducted. A meta-analysis comparing the averages was conducted on studies that reported numerical values.
Additionally, meta-analysis of variance and meta-regression analyses were performed.
Results: Meta-analysis of the 34 studies using the random-effects model revealed that the use of aromatherapy was highly effective
in improving sleep problems such as insomnia, including quantitative and qualitative sleep effects (95% confidence interval [CI], effect
sizes =0.6491). Subgroup analysis revealed that the secondary outcomes including stress, depression, anxiety, and fatigue were
significantly effective. The single aroma inhalation method was more effective than the mixed aroma inhalation method. Among the
single inhalation methods, the lavender inhalation effect was the greatest.
Conclusion: Inhalation aromatherapy is effective in improving sleep problems such as insomnia. Therefore, it is essential to develop
specific guidelines for the efficient inhalation of aromatherapy.
Ethics and dissemination: Ethical approval is not required because individual patient data are not included. The findings of this
systematic review were disseminated through peer-reviewed publications or conference presentations.
PROSPERO registration number: CRD42020142120.
Abbreviations: Actigraphy =activity recorder, AMED =Allied and Complementary Medicine Database, BDI =Beck Depression
Inventory, CENTRAL =Cochrane Central Register of Controlled Trials, CINAHL =Cumulative Index to Nursing and Allied Health
Literature, DSM-5 =Diagnostic and Statistical Manual of Mental Disorders-5, ES =effect sizes, FSI =fatigue symptom inventory,
HAMD =Hamilton Depression Scale, ISI =insomnia severity index, KCI =Korea Citation Index, KISS =Korean studies Information
Service System, KMbase =Korean Medical Database, MEDLINE =Medical Literature Analysis and Retrieval System Online, or
MEDLARS Online, meta-ANOVA =meta-analysis of variance, OASIS =Oriental Medicine Advanced Searching Integrated System,
PICOS =Participants, Intervention, Control, Outcomes & Study Design, PRISMA =Preferred Reporting Items for Systematic
Editor: Yoshihiro Shidoji.
Consent for publication: Not applicable.
Availability of data and material: Not applicable.
This research was funded by the Ministry of Health and Welfare and was supported by the Korea Health Industry Promotion Agency’s Health and Medical Technology
R&D Project (Grant number: HI20C1951). The funding source will have no input in the interpretation or publication of the study results.
The authors declare that they have no conflict of interest.
The datasets generated during and/or analyzed during the current study are not publicly available, but are available from the corresponding author on reasonable
request.
a
Rare Diseases Integrative Treatment Research Institute, Wonkwang University, Jangheung Integrative Medical Hospital, Anyang-myeon, Jangheung-gun, Jeollanam-
do,
b
Center of Amyotrophic Lateral Sclerosis & Motor Neuron Disease, Wonkwang University Gwangju Medical Hospital, Nam-gu, Gwangju,
c
Department of Korean
Neuropsychiatry Medicine, Wonkwang University, Iksan,
d
Department of Korean Neuropsychiatry Medicine & Inam Neuroscience Research Center, Wonkwang
University Sanbon Hospital, Gunpo, Republic of Korea.
∗
Correspondence: Hyung Won Kang, Department of Korean Neuropsychiatry Medicine, Wonkwang University, Iksan, 460, IKsan-daero, Iksan-si Jeollabuk-do, Republic
of Korea/Department of Neuropsychiatry of Korean Medicine & Inam Neuroscience Research Center, Wonkwang University Sanbon Hospital. 321, Sanbon-ro Gunpo
City, Gyeonggi-do 15865, Republic of Korea (e-mail: dskhw@wku.ac.kr).
Copyright ©2021 the Author(s). Published by Wolters Kluwer Health, Inc.
This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial License 4.0 (CCBY-NC), where it is permissible to
download, share, remix, transform, and buildup the work provided it is properly cited. The work cannot be used commercially without permission from the journal.
How to cite this article: Cheong MJ, Kim S, Kim JS, Lee H, Lyu YS, Lee YR, Jeon B, Kang HW. A systematic literature review and meta-analysis of the clinical effects
of aroma inhalation therapy on sleep problems. Medicine 2021;100:9(e24652).
Received: 5 June 2020 / Received in final form: 26 November 2020 / Accepted: 10 January 2021
http://dx.doi.org/10.1097/MD.0000000000024652
Systematic Review and Meta-Analysis Medicine®
OPEN
1
Reviews and Meta-analysis, PSG =polysomnography, PSQI =Pittsburgh Sleep Quality Index, PSS =perceived stress scale, RCT =
randomized controlled trial, RISS =research information service system, SE =sleep efficiency, SOL =sleep onset latency, SSQ =
Stanford Sleep Questionnaire, STAI =state-trait anxiety inventory, TST =total sleep time, WASO =wake-up sleep on time, WHIIRS =
Women’s Health Initiative Insomnia Rating Scale.
Keywords: aromatherapy, inhalation, insomnia, meta-analysis, sleep problems, systematic literature review
1. Introduction
During sleep, humans undergo physical and mental stress
recovery and rejuvenation.
[1–3]
Sleep deprivation is common
among the current generation and up to 18% of the world’s
population experiences insomnia.
[4,5]
In Korea, >2 million
people were diagnosed with insomnia over a period of 5 years
(2013–2017), according to the National Health Insurance
Corporation. A meta-analysis on sleep-related studies assessed
the factors related to sleep disorders and found that stress, a
psychological result, exhibited the highest correlation with sleep
disorders.
[5,6]
However, stress coexists with other diseases in the
current generation, and therefore it is challenging to treat sleep
disorders by only addressing the stress. Additionally, prescrip-
tions for sleep problems include sleep inducers and sleeping pills,
which may lead to other problems in daily life.
[7]
For example, a
sleep disorder patient led to a traffic accident a day after ingesting
sleeping pills, which stay in the body longer than other drugs.
[8]
Recently, interest in programs using psychological interventions
and complementary alternative medicine has increased to reduce
the side effects of prescription drugs and improve the quality of
life of insomnia patients.
[9]
However, there are limitations in
these program applications to those with sleep disorders. Most
programs last 50minutes per session and are performed at least
once a week. As sleep disorder programs are conducted for a
longer period rather than a single session,
[5]
adults that work
during the day or at night
[10–12]
have difficulties in participating
in such programs. Additionally, those with sleep disorders
experience depression, anxiety, and panic disorder, which also
leads to difficulties in program participation.
[13–16]
Aroma inhalation therapy for treating sleep disorders has
recently been gaining great interest. Inhalation of aromatic oil
particlesthat stimulate the olfactory sense, directlyaffect the central
nervous system responsible for controlling human emotions and
physiological functions. It regulates the autonomic nervous system,
endocrine system, and immune system, leading to therapeutic
effects on the body.
[17]
Another advantage of aromatherapy is that
individuals can choose their preferred scents, and those that cannot
participate in sleep disorder programs can also undergo aroma-
therapy regardless of thetime and place. In Korea, recent studies on
aroma inhalation therapy have been reported in professional
groups (such as night shift nurses, metropolitan workers)
experiencing sleep disorders.
[11,12]
However, information on
specific methods such as the type of aroma used and the usage
time is unclear.
[14]
Therefore, this study quantitatively analyzed the
effects of aroma inhalation therapy for sleep disorders and assessed
the most effective oil for sleep. This study provides information on
the aroma that can be used by anyone to improve sleep problems in
their daily life and obtain the maximum beneficial effects of sleep.
2. Methods
2.1. Study registration
This systematic review was registered in the International
Prospective Register of Systematic Reviews (PROSPERO)
(registration number, CRD42020142120) on March 02, 2020,
and has been reported following the Preferred Reporting Items
for Systematic Reviews and Meta-analysis (PRISMA) guidelines
for systematic reviews.
[18]
2.2. Study design
This systematic literature review and meta-analysis analyzed the
reported effects of the aroma inhalation method on the
improvement of sleep problems.
2.3. Data sources
The literature search was conducted by 3 researchers and 2
methodologists with information collated from domestic and
foreign databases, including 5 Korean-language databases
(Oriental Medicine Advanced Searching Integrated System
[OASIS], Korean Studies Information Service System [KISS],
Research Information Service System [RISS], Korean Medical
Database [KMbase], and Korea Citation Index [KCI]) and 6
English-language databases (MEDLINE via PubMed, EMBASE
via Elsevier, the Allied and Complementary Medicine Database
[AMED] via EBSCO, the Cochrane Central Register of
Controlled Trials [CENTRAL], the Cumulative Index to Nursing
and Allied Health Literature [CINAHL] via EBSCO, and
PsycARTICLES via ProQuest). We also searched the “gray
literature”that including unpublished articles. There were no
language restrictions.
2.4. Search strategies
A presearch was conducted based on the MeSH term for the
treatment of sleep disorders using aromatherapy. Subsequently,
search terms that were included in the search strategy were
implemented following the procedure. The search terms were as
follows: “Insomnia,”“Sleep Disorder,”“Sleep Problem,”
“Aroma Therapy,”and “Aroma Inhalation therapy.”In
addition, for Ovid-MEDLINE, EMBASE, and SIGN, and
PubMed, search filters used in the Shojania et al
[19]
study were
used to increase the specificity of the searches. Furthermore,
existing systematic literature reviews and Cochrane reviews of
relevant topics were considered when constructing the search
strategy.
2.5. Study selection
2.5.1. Types of studies. Studies selected were the randomized
control trials (RCTs). Studies that used inappropriate random
sequence generation methods such as alternate allocation were
excluded. Studies included systematic reviews in experimental
studies where meta-analyzed figures were provided, which
investigated sleep disorders and sleep problems associated with
the inhalation of aroma oil. Specifically, the selection of the thesis
was done using the criteria of the core questionnaire PICO
(Patient/Participants/Population/Problem, Intervention, Com-
parison, and Outcome) in this study. Furthermore, to check
Cheong et al. Medicine (2021) 100:9 Medicine
2
the effectiveness of aroma inhalation in improving sleep
problems, the types of aroma, and methods of aroma mixing
were included as adjustment parameters. However, other designs
such as in vivo, in vitro, case reports or studies, retrospective
studies, qualitative studies, uncontrolled trials, and trials, that
failed to provide detailed results, were excluded. Details of the
study design are outlined in Table 1.
2.5.2. Types of participants. We included studies on people
with undiagnosed sleep problems and patients, aged 20 to 60
years, with sleep disorders diagnosed using standardized
diagnostic tools such as the Diagnostic and Statistical Manual
of Mental Disorders-5. There were no restrictions on the sex or
race of the participants.
2.5.3. Types of interventions. The intervention methods were
aroma inhalation methods.
2.6. Types of outcome measures
2.6.1. The primary outcomes. Primary outcomes were sleep
quantitative and qualitative inventories
a. Effect on the quantitative sleep time, which was evaluated
using the following measures:
(1) The activity recorder (actigraphy)
[20]
records the activity
during sleep when worn on the wrist or ankle.
(2) Polysomnography (PSG)
[21]
test measures the physiologi-
cal changes that occur during sleep by measuring the EEG,
EMG, ECG, snoring, respiration, and diagnoses of the
disorder
(3) The sleep diary
[22,23]
used to measure the patient’s sleep
habits, sleep hygiene, and sleep problems for 2 weeks, and
to evaluate the progress of the treatment.
(4) Total sleep time (TST)
[24]
: insufficient sleep if total sleep
time was lower than.
[25]
(5) Sleep onset latency (SOL)
[26,27]
: insufficient sleep when the
elevation delay time was more than 30 minutes.
(6) Wake-up Sleep On Time (WASO)
[28]
: If the awakening
time was >30 minutes after the elevation, the sleep is
considered insufficient.
(7) Sleep Efficiency (SE)
[29]
: Sleep efficiency of 85% was
considered insufficient.
b. Effect on quality of sleep
Patient reporting tools used, with proven reliability and
validity, are as follows:
(1) The Pittsburgh Sleep Quality Index (PSQI)
[30]
consists
of 19 self-reporting questions about sleep quality and
discomfort over the past month. The total score ranges from
0 to 21; the lower the total score, the better the quality of
sleep, and the higher the total score, the worse the sleep
quality.
(2) The Insomnia Severity Index (ISI),
[31]
developed to assess
insomnia, is a self-reporting measure that comprises a total of
7 questions. It is a 5-point scale with higher scores indicating
more serious insomnia.
(3) The Medical Outcome Study Sleep Scale,
[32]
consists of 12
questions, measured in the range of 0 to 100; the lower the
score, the better the quality of sleep.
(4) The Stanford Sleep Questionnaire (SSQ)
[33,34]
has 7 classes,
with subjective sleepiness levels of 1 to 7; lower scores
indicate better sleep quality.
(5) The Women’s Health Initiative Insomnia Rating Scale
(WHIIRS)
[35]
consists of 5-item scales for sleep initiation
and maintenance and evaluates the subjective sleep quality.
The lower the score, the better the sleep quality.
Table 1
Study type selection according to PICO.
Criteria factor Standard contents
Research method RCTs conducted with the quantitative research method (except for retrospective studies, in vivo, in vitro, case reports or studies,
qualitative studies, and uncontrolled trials)
Research design RCT studies
Purpose Reasonable for the research purposes should be revealed.
Participants/Patients Participants with insomnia and sleep disorders diagnosed using standardized diagnostic tools such as the DSM-5; there was no
restriction on the sex or race of the participants or sleep problems and disorders.
Intervention/Moderate variables Direct/Indirect (such as necklace) inhalation method of aromatherapy
Comparator There was no restriction.
Outcomes -Primary outcomes
Effect on quality of sleep
(1) Pittsburgh Sleep Quality Index (PSQI)
(2) SHV (Synder-Halpern and Verran, 1987)
(3) Insomnia Severity Index
(4) Korean Sleep Scale A
(5) Q.O.S (Quality of Sleep)
(6) VAS
(7) Stanford Sleepiness Scale
(8) NRS (Numeric Rating Scale)
-Secondary outcomes
(1) Depression (Beck Depression Inventory)
(2) Stress (Physical stress, Psychological stress)
(3) Status anxiety
(4) Fatigue
Data statistics All sorts of values, such as mean, standard deviation, tand fvalues, calculated effect size
DSM-5 =Diagnostic and Statistical Manual of Mental Disorders-5, RCT=randomized controlled trial.
Cheong et al. Medicine (2021) 100:9 www.md-journal.com
3
(6) Sleeping measure
[36]
consists of 15 questions and is a 4-point
scale. It has a range of up to 60 points from a minimum of 15
points, and a higher score indicates better sleep.
2.6.2. The secondary outcomes. Secondary medical outcomes
reported were depression, stress, anxiety, and decreased fatigue.
They were assessed as follows;
(1) Change in the degree of depression as measured by validated
assessment tools such as the Hamilton Depression Scale
(HAMD)
[37]
and the Beck Depression Inventory (BDI).
[38]
(2) Stress was measured using the perceived stress scale
(PSS).
[39,40]
(3) Anxiety was measured using the State-Trait Anxiety
Inventory State version (STAI).
[41]
(4) Fatigue was measured using the fatigue symptom inventory
(FSI).
[42]
2.7. Study selection
Screening procedure is as follows. Domestic and international
online databases were searched. A total of 7924 articles, including
7200 articles registered with keywords of “aroma”and “sleep
problems”from 2000 to 2019 and 724 additional articles from
other search sources, were collected. Among them, a total of 1240
papers that were duplicates and 5643 articles that were not
conducted on humans and subjects with sleep problems, were
excluded. A total of 21 articles on meta-analysis, including
systemic literature reviews and 659 studies on non-aroma
inhalation therapy were excluded from the remaining 1041
articles. A total of 301 studies that did not report improved sleep
and 26 articles that did not correspond to Participants, Interven-
tion, Control, Outcomes & Study Designfor the systemic literature
review were excluded.In the end, a total of 34 articles were selected
and numerical values were reported in all these articles. The meta-
analysis was performed and results were reported following the
PRISMA guidelines (Guidelines Flow Diagram).
[18]
2.8. Data coding extraction
Using a standardized data collection form, 3 independent
researchers cross-checked the data extraction process. Discrep-
ancies were resolved through discussion with other researchers.
The coding plate was constructed, as shown in Table 2, to analyze
the extracted data. The coding of data for this study was based on
a meta-analysis of various aromatherapy effects on the sleep
disorders reported by Hwang and Shin.
[3]
In addition, based on
the paper by Lillehei and Halcon,
[43]
basic information (author,
year, and title), method of intervention (direct or indirect
aromatherapy), and interventions (aroma type: single or mixed,
study group characteristics: general, patient, etc) were included in
the proceedings (total sessions, weekly sessions, session hours).
To ensure the reliability of the meta-analysis coding, one
researcher with experience in the meta-analysis, one researcher
with a major in applied statistics of research methodology and
meta-analysis, and one specialist from oriental neurological
psychiatry that used aromas to treat insomnia, were cross-coded
as well. During the course of coding, the paper, which showed no
consensus or required more confirmation, an expert on insomnia
was consulted. The coding analysis table is shown in Table 2.
2.9. Quality assessment of articles
Quality assessment of articles was conducted using Review
Manager version 5.3 software (Cochrane, London, UK), to assess
the risks of random selection, allocation concealment, blinding of
participants and personnel, blinding of outcome assessment,
incomplete outcome data, selective reporting, and other biases.
The risk was evaluated as “low, high, and unclear.”
[44]
2.10. Literature evaluation and sorting
Results from the included 34 papers following the systematic
literature reviewwere analyzed, encoded, and arranged into forms.
The forms included the selection of research design, number of
participants, criteria for participant selection and exclusion,
measurement variables and tools, result variables, and statistical
values. To ensure accuracy during the process, 2 researchers
independently conducted the evaluations, and the results were
cross-checked and compared for inter-rater agreement.
2.11. Meta-analysis
The data analysis procedure included the verification of
publication bias errors, verification of homogeneity and
Figure 1. Guidelines flow diagram.
Cheong et al. Medicine (2021) 100:9 Medicine
4
heterogeneity, calculation of total effect size, and meta-analysis of
variance (meta-ANOVA) for aromatherapy over time and period
of intervention (meta-ANOVA with aroma type, aroma single or
mixed/research group, and aroma direct and indirect effects). In
addition, the sizeof the calibration effect (Hedgeg) was used to give
weight to the number of cases studied. This required Hedge g to be
calibrated due to the intergroup effect size and Cohen dtends to
overestimate the effect size when the sample is small.
[45]
Finally, for
the analysis of the data, such as effectiveness size and homogeneity
verification, a statistical program for meta-analysis (Comprehen-
sive Meta-Analysis version 2.0 [Biostat Inc, NJ]) was used. All
analysis process was consulted by a meta-analysis expert.
2.12. Additional analyses
For additional analyses, meta-regression analysis was performed
using the primary and secondary outcomes as continuous
variables.
2.13. Ethics and dissemination
Ethical approval was not required because the data used in this
systematic review were not individual patient data; therefore,
there were no concerns regarding privacy.
3. Results
3.1. Quality assessment results
For the quality assessment of articles, there was a high risk of
bias in blinding of participants and personnel, which was a
performance bias, and in the allocation concealment and random
sequence generation, which were selection biases. Additionally,
an unclear risk of bias was observed for blinding of outcome
assessment, which was detection and other biases. However, low
risk was observed for incomplete outcome data and selective
reporting (Figs. 2 and 3).
3.2. Systematic literature review evaluation and sorting
results
The systemic literature review results are as follows. Among the
34 studies (Tables 3 and 4), 13 articles (37.2%) and 21 articles
(62%) used single and mixed aromas, respectively. Among the 13
articles that used single aroma oil for inhalation, lavender aroma
oil was used in 10 studies (76%). Additionally, lavender was used
in 16 papers that used mixed aromas. This finding suggests a bias
of oils related to sleep and it is necessary to assess why lavender
aroma improves sleep. A total of 3, 13, and 18 articles performed
indirect inhalation (necklace, etc), a mix of indirect and direct
inhalation, and direct inhalation, respectively. Tools used to
analyze main effects and evaluate improvements in sleep
disorders included the sleep scale A developed in Korea (9
studies), Pittsburg sleep quality index (4 studies), and Snyder-
Halpern and Verran
[46]
sleep scale (8 studies). Assessment of
secondary effects showed both decreased psychological problems
such as depression and anxiety, and the physiological functions,
including blood pressure and fatigue. As a result, the systematic
literature review demonstrated that aroma inhalation therapy
was beneficial in improving sleep.
Table 2
Data coding extraction.
Variables Moderator
Outcomes Primary outcomes
Secondary outcomes
Kinds of aroma Single Lavender, phytoncide, rosemary,
Rosadamascence
Mixed Sweet orange, Rosewood marjoram
Ylang-Ylang, Bergamot, Basil exotic
Cymbopogon marini
Aniba rosaeodora, Roman Chamomile
Citrus bergamia
Grapefruit, Citrus paradisi,
Geranium, Neroli,
Citrus aurantium L. var
Subjects Cardiac diseases Patients with cardiac stents
The heart disease
Participants Patients Section Cesarean section
Colectomy, hysterectomy
pneumonectomy
Psychological disorders or problems Sleep disorders such as insomnia, sleep problems, anxiety disorder, schizophrenia
ETC. Pain patient, essential hypertension, patient undergoing hemodialysis
Coronary arteriography patient, patient in an intensive care unit
Non-patients
Job kind Night shift nurses, subway worker (night shift)
Nation Domestic Korea
Others
Inhalation Direct
Methods Indirect
Cheong et al. Medicine (2021) 100:9 www.md-journal.com
5
3.3. Publication bias analysis
The final 34 selected papers, shown in Table 5 (effect size case =
273), were analyzed for publication bias. In this study, we
examined the publication bias (Figs. 2 and 3) of the papers
collected through the funnel plot (Fig. 4) and analyzed the bias of
the samples in a complementary manner using the estimation and
fill method. As shown in Figs. 5 and 6, the funnel plot is
somewhat symmetrical and had no issues with bias.
[47]
In
addition, sensitivity analysis, which is the estimation additive
(Trim & Fill) of the complementary methods of Duvall and
Tweedie,
[48]
resulted in the same calibration and observation
values of the coordinated study (Table 6).
3.4. Verification of homogeneity and overall effect size of
aroma inhalation effect on sleep problem
The results of the evaluation of the total effect size of
aromatherapy, calculated from 172 effect sizes culled from the
34 studies included in the present study, are shown in Table 4.
The homogeneity test was performed at a significance level of
P<.05, resulting in the application of the random effect model,
which was determined to be heterogeneous by rejecting the null
hypothesis at 193.515 (P<.01).
[49]
The value of I, which
represents the ratio of the total variance contrast study, was
82.947, which is >50 and thus had significant heterogeneity. In
addition, since each study was assessed differently by different
researchers, estimates of population effect size were not the same.
Therefore, the analysis reported in this paper was conducted
using a random-effect model, since the size of the effects assessed
by the researchers varied, and was statistically significant through
heterogeneity analysis (Table 7). The total effect size for sleep
problems was 0.650 and the 95% confidence interval for the total
effect size ranged from 0.542 to 0.757. This is equivalent to 73%
to 76% if the U-index, the cumulative distribution analysis
method of effect size, is presented. The effect size of 0.65 implies
that the control group showed 50% effectiveness in the
experiment, whereas the effectiveness ranged from 73% to
76% for the experimental group. Therefore, the experimental
group exceeded the median value of the control group (50% for
the control group) with a success rate of 73% to 76%. Thus, the
program effectiveness of the experimental group that used
aromatherapy for sleep problems can be interpreted as 23 to 26
higher than the program effectiveness of the control group
(Rosenthal and Rubin
[50]
). The criteria of Cohen
[51]
and
Wolf
[52,53]
were to interpret the magnitude of the effects assessed
in the meta-analysis. Cohen
[51]
interpreted the average effect size
(d) below 0.2 as a small effect size, 0.5 as a medium effect size,
and 0.8 as a large effect size. Wolf
[52]
has an educational
significance if its effect size is >0.25. At least 5 studies, the criteria
for interpretation were presented as significant at a practical and
therapeutic level. According to this criterion, the overall average
effect size of the aroma inhalation method for sleep problems was
0.65, which was greater than the middle effect size. Thus, the
groups that conducted the aromatherapy program had a more
significant outcome on the overall average effect size compared
with those that did not (Fig. 5).
3.5. Effect sizes of secondary outcomes
After each classification for negative effects analysis, the
differences between each group, and the size of the effects were
verified. The effect size of each program was as follows:
stress (effect sizes [ES](g) =0.838, P<.01), (anxiety (g) =0.599,
P<.01), other (blood pressure, appetite, pain, etc) (ES(g) =0.592,
P<.01), (depression(g) =556, P<.01), and (fatigue(g) =0.544,
P<.01), demonstrating a statistically significant effect size.
However, the differences in effects between the groups were not
statistically significant. That is, even though inhalation of aromas
had a significant effect on stress, anxiety, depression, and fatigue,
it did not exhibit a statistically significant difference (Table 8).
Figure 2. Risk of bias included in the study.
Cheong et al. Medicine (2021) 100:9 Medicine
6
3.6. Effect size according to intervention factors
In the meta-analysis, the modulating effect analysis according to
the arbitrator more directly validated the difference in effect size
among subgroups and allowed the effect on the average effect size
to be verified through the study-level variables that describe the
effect size, that is, the covariates or modifiers. In this study, we
attempted to determine the statistical significance by conducting
differential verification and regression analysis for each variable.
3.7. Individual effect size and meta-ANOVA test of
category
3.7.1. The types of aroma (single or mixed). After classifying
the effects of single and compound aromas on sleep problems, the
differences between groups and their sizes were analyzed. The
difference in the size of the effects between the 2 groups (single
aromas vs composite aromas) was (ES(g) =0.720, P<in the case
of single aromas .01), and (ES(g) =0.576, P<.01) for composite
aromas; each effect size was statistically significant. In addition,
the effect of using a single aroma was significantly higher than
that of the composite aromas (Q=2.38(1) and P<.05) (Table 9).
3.7.2. Analysis of effect size based on types of study
subjects (clinical group and general [shift workers and
non-shift workers]). The clinical (ES(g) =0.782, P<.01) and
general groups (ES(g) =0.538, P<.01) (where the effect of the
inhalation of aromas was statistically significant) exhibited a
statistically significant inter-difference (Q(df) =6.759(1), P
<.05). This means that the aroma inhalation effect is also a
night shift in the general population (ES(g) =0.682, P<.01),
General (ES(g) =0.483, P<.01); each of the aroma inhalation
was statistically significant for sleep but the difference between
groups in the general population was not significant. This
means that aroma inhalation has varying effects on different
sleep disorders, without any significant difference recorded
between the groups for shift workers or non-committal groups
(Table 10).
3.7.3. Analysis of effect size based on research duration of
the time and times. As a mediator, the size of the effect of aroma
inhalation on sleep problems was analyzed for 24 hours and before
bedtime (1–3 times), that is, if aroma was inhaled from 1 to 3 times
before bed (ES(g) =0.661, P<.01), or if a 24 hours aroma necklace
was worn or aroma was continuously inhaled using tools for
indirect inhalation (ES(g) =0.476; P<.01). This resulted in a
greater effect of premagnetic inhalation than a 24hours duration,
indicating a statistically significant difference (Q(df)=5.637,
P<.05). Therefore, continuous inhalation of 1 to 3 times was
more effective than 24hours indirect inhalation for the ameliora-
tion of sleep problems, and that the differences in direct and indirect
inhalation, rather than the duration of time, elicited a change in the
size of the effects. In addition, after analyzing the effects of 1 to 3
cycles of inhalation before going to bed (the first time was [ES(g)=
0.699 and P<.01], [ES(g)=0.645 and P<.01], the third [ES(g)=
0.534, P<.01]), each group showed a statistically significant effect
but differences between groups were not statistically significant.
Although there were differences in the effects of direct and indirect
inhalation methods, the session not resulting in a statistically
significant change could be due to the size of the effects. Next, the
effectiveness of aroma inhalation in alleviating sleep problems was
analyzed on a national scale; Korea (ES(g)=0.724; P<.01) and
other countries (ES(g)=0.470, P<.01). A statistically significant
difference (Q(df)=7.766, P<.01) was observed. This was also
observedin the SR analysis howeverthe studies of aroma inhalation
methods for improvement of sleep disorders orsleep problems were
statistically significant compared with other countries. This
indicates that in Korea, there is an active study of the effect of
aroma inhalation onsleep disorders andsleep problems, andas well
as an interest in their efficacy. The results are shown in Table 5.
Figure 3. The risk of bias using RevMan.
Cheong et al. Medicine (2021) 100:9 www.md-journal.com
7
Table 3
Studies included in the systematic review and meta-analysis.
Ko, Ye Jung. Effects of lavender fragrance inhalation method on sleep, depression and stress of institutionalized elderly. Journal of East-West Nursing Research, 2012, 18.2:
74–80.
Kim, O.J. The effect of aroma inhalation method on stress, anxiety and sleep pattern in patients undergoing hemodialysis. Unpublished master’s thesis, Chung-Ang University,
Seoul, 2007.
Park, Sihyun, et al. The effect of aroma inhalation therapy on fatigue and sleep in nurse shift workers. Journal of East-West Nursing Research, 2012, 18.2: 66–73.
Choi, Eun-Mi; Lee, Kyung-Sook. Effects of aroma inhalation on blood pressure, pulse rate, sleep, stress, and anxiety in patients with essential hypertension. Journal of Korean
Biological Nursing Science, 2012, 14.1: 41–48.
Oh, Hyun-Mi; Jung, Geum-Sook; Kim, Ja Ok. The effects of aroma inhalation method with roll-on in occupation stress, depression and sleep in female manufacture shift
workers. Journal of the Korea Academia-Industrial cooperation Society, 2014, 15.5: 2903–2913.
Kim, WonJong; Hur, Myung-Haeng. Inhalation effects of aroma essential oil on quality of sleep for shift nurses after night work. Journal of Korean Academy of Nursing, 2016,
46.6: 769–779.
Park, S., et al. The effects of aroma therapy on sleep disorder patients with musculoskeletal pain. J Oriental Rehab Med, 2010, 20: 215–230.
Choi, Jae-won, et al. Phytoncide aroma inhalation and exercise combination therapy mood state, college life stress and sleep of college students. Journal of Digital
Convergence, 2016, 14.12: 633–644.
Lee, Sun-Ok; Hwang, Jin-Hee. Effects of aroma inhalation method on subjective quality of sleep, state anxiety, and depression in mothers following cesarean section delivery.
Journal of Korean Academy of Fundamentals of Nursing, 2011, 18.1: 54.
Lee Gyeong-Jae. A Study on the Effect of Aroma on Sleep and Fatigue of Subway Crew. Graduate School of Glocal Integration at Sunmoon University: Natural healing studies
2018. Master thesis.
Choi Seo Yeon. (The) effects of aroma oil inhalation therapy on appetite, sleep, and stress in middle-aged overweight women: a randomized controlled trial. Graduate School of
Chung-Ang University: Graduate School of Nursing and Nursing Studies. 2016. Doctoral thesis.
Lee Sook-hyun. Effects of Aromatherapy on Stress Response, Sleep and Immunity in Middle-Aged Women. Graduate School of Eulji University: Nursing and Nursing Studies.
2018. Doctoral thesis.
Lee Yoo-jin. The Inhalation Effects of Aroma Essential Oil on Stress, Sleep Quality and Immunity of Shift work Nurses: A Parallel group Randomized Controlled Trial. Graduate
School of Clinical Nursing at Eulji University: Clinical nursing education major clinical nursing education. 2018. Master thesis.
Cho, M.Y. The effects of Aromatherapy on Anxiety, Vital sign & Sleep of PCI patients hospitalized in intensive care units. Unpublished master’s, Eulji University, Daejeon, 2011.
Choi Myung-ja. The Effects of Aromatherapy on Alleviation of Stress Among Schipzophrenic Patients. Graduate School of Health at Chosun University: Alternative Medicine.
2006.
Lee, M. H. The effect of aroma therapy on the comfort, anxiety and sleep of heart stent spiled patients hospitalized in intensive care unit. Unpublished master’s, Dong-A
University, Pusan, 2006.
Cho Eun-hee. The Effects of Aromatherapy on Stress, and Sleep Quality in ICU patients. Graduate School of Clinical Nursing at Eulji University: Clinical nursing education major,
clinical nursing education. 2017.
Lee Jin-kyung. The Effect of Aroma Inhalation on Fatigue and Sleep: Focused on Mothers with Preschool Children. Graduate School of Alternative Medicine at Kyunggi
University: A major in alternative medicine and psychiatric treatment. 2017.
Min Kyung-min. The effect of inhaling orange, lavender and chamomile roman aromas on the quality of sleep and fatigue of shift working nurses. Chung-Ang University
Graduate School: Graduate School of Nursing and Nursing Studies. 2015.
Kim Hye-yeon. (The) effect of aromatheray on anxiety and sleep of patients with coronary angiography. Dankook University Graduate School: Graduate School of Nursing and
Clinical Nursing in 2008.
So Hae-Ran. The Effect of Aroma Inhalation on Pain, Anxiety, Vital Sign and Sleep of Patients with Colon Resection. Gachon University Graduate School of Nursing: Senior
Nursing Education. 2012.
Choi Jeong-hee. Effects of Aroma Inhalation Therapy on Pain, Stress, Nausea·Vomiting and Sleep of Patients Following a Hysterectomy. Graduate School of Gachon University:
Nursing for the Elderly 2013.
Lee Won-jin. Effects of Aroma Inhalation to Blood Pressure, Pain and Quality of Sleep in Patients with Pulmonary Resection. Graduate School of Ewha Women’s University:
Department of Nursing Science. 2016.
Jeon WhaYoung. Aromatherapy effects on sleep improvement and depression in middle-aged women. Chosun University: Alternative Medicine, 2015.
Nam Jung-ja. Effects of aromatherapy and massage on sleep disturbance and problematic behaviors on elderly with dementia. Graduate School of Ewha Womans University:
Department of Nursing Science, 2008.
Lillehei, Angela Smith, et al. Well-being and self-assessment of change: Secondary analysis of an RCT that demonstrated benefit of inhaled lavender and sleep hygiene in
college students with sleep problems. Explore, 2016, 12.6: 427–435.
Nematolahi, Pouya, et al. Effects of Rosmarinus officinalis L. on memory performance, anxiety, depression, and sleep quality in university students: a randomized clinical trial.
Complementary therapies in clinical practice, 2018, 30: 24–28.
Lee, Mi-kyoung, et al. The effects of aromatherapy essential oil inhalation on stress, sleep quality and immunity in healthy adults: Randomized controlled trial. European Journal
of Integrative Medicine, 2017, 12: 79–86.
Afshar, Mahnaz Keshavarz, et al. Lavender fragrance essential oil and the quality of sleep in postpartum women. Iranian Red Crescent Medical Journal, 2015, 17.4.
Lee, Sung-Hee. Effects of aroma inhalation on fatigue and sleep quality of postpartum mothers. Korean Journal of Women Health Nursing, 2004, 10.3: 235–243.
Hajibagheri, Ali; Babaii, Atye; Adib-hajbaghery, Mohsen. Effect of Rosa damascene aromatherapy on sleep quality in cardiac patients: a randomized controlled trial.
Complementary therapies in clinical practice, 2014, 20.3: 159–163.
Karadag, Ezgi, et al. Effects of aromatherapy on sleep quality and anxiety of patients. Nursing in critical care, 2017, 22.2: 105–112.
Goel, Namni; Kim, Hyungsoo; Lao, Raymund P. An olfactory stimulus modifies nighttime sleep in young men and women. Chronobiology International, 2005, 22.5: 889–904.
Moeini, Mahin, et al. Effect of aromatherapy on the quality of sleep in ischemic heart disease patients hospitalized in intensive care units of heart hospitals of the Isfahan
University of Medical Sciences. Iranian journal of nursing and midwifery research, 2010, 15.4: 234.
Cheong et al. Medicine (2021) 100:9 Medicine
8
3.8. Additional analysis
3.8.1. A regression analysis of the main effects and sub-
effects of the aroma inhalation period. For each study, the
effect size was analyzed according to the total number of sessions
and was reanalyzed after the number of aroma inhalation
sessions was coded as a continuous variable. As a result, the slope
(b=) in the main effect size (0.00367, P<.01) was statistically
significant (Intercept: 0.50136, P<.01) (t=0.13179, P<.01).
These results show that the effect increases as the total number of
sessions increases. In addition, the slope (b=) in the regression
analysis of the size of the negative effects (0.00405, P=.01) and
intercept (0.47506, P<.01) was statistically significant (t=
0.24879; P<.01). This shows that the impact of the negative
effects also increased as the total number of sessions increased.
The regression results for assembly acquisition are the same as
those outlined in Table 11 and Figs. 6 and 7.
4. Discussion
Sleep disorders, including insomnia, are one of the most common
diseases that affect people in the current modern society.
[54,55]
Persistent sleep deprivation leads to the consumption of sleep
inducers and sleeping pills.
[56,57]
However, some of these drugs tend
to lead to overdose and addiction, and the sleep symptoms from the
drugs persist can until the next day, impacting daily life activities.
[8]
As a result, discussions on various alternative treatments such as
aromatherapy have recently gained attention.
[21]
When the aroma is
inhaled, the aroma molecules enter the olfactory epithelium through
the nasal roof and stimulate the olfactory neurons. This leads to the
secretion of hormones in the pituitary gland as well as peptides.
[17]
In
particular, endorphin, which is one of the secreted peptides, is
effective for treating sleep disorders caused by depression and
anxiety,andinreducingpainandchronicstress.
[58]
This study conducted a systematic literature review and meta-
analysis to assess the clinical efficacy of aroma inhalation therapy
in the treatment of sleep problems in patients diagnosed with
insomnia, using published reports until June 2019. Previous
studies that analyzed the effects of aroma on sleep problems were
mostly conducted with massage therapy in parallel.
[3]
However,
massage therapy requires help from someone else and there is a
limit on it being performed alone.
[59]
Therefore, this study
analyzed studies that assessed the aroma inhalation therapy as the
sole manner for reducing sleep problems without much effort and
help from anyone else.
Figure 4. Funnel plot of the publication bias.
Cheong et al. Medicine (2021) 100:9 www.md-journal.com
9
Table 4
Systematic literature review evaluation and sorting results.
Study (year) Aroma (single/mixed) Application Research design Nation Samplesize (n) Primary outcome Secondary outcome Subject character
1. Ko (2012) Lavender (single) Direct inhalation Equivalent control /RCT Korea. 39 (exp: 18, cont: 21) Korea Sleep Scale A(+) Depression()
Stress()
An elderly person living in a
facility
2. Kim et al (2007) Lavender, sweet orange
2:1 (Mixed)
Direct inhalation Equivalent control /RCT Korea. 50 (exp: 25, cont: 25) Korea Sleep Scale A(+) Stress ()
Anxiety()
Chronic hemodialysis
patients
3. Park et al (2007) Lavender, Rosewood 1: 1
(Mixed)
Direct inhalation Nonequivalent control
/RCT
Korea. 60 (exp: 30, cont: 30) Sleep Quality Scale(+) Fatique() Nurse Shift Workers
4. Choi et al (2012) Lavender Marjoram, Ylang-Ylang
4: 3: 3 (Mixed)
Direct inhalation Equivalent control /RCT Korea 36 (exp: 20, cont: 16) Sleep state()
SleepSatisfaction(+)
Stress()
Anxiety()
Patients with essential
hypertension
5. Oh et al (2014) Bergamot, Lavender, Ylang-
Ylang, Jojoba oil 1: 1: 1: 1
(Mixed)
Inirect inhalation Nonequivalent control
group/RCT
Korea 52 (exp: 26, cont: 26) Korea Sleep Scale A(+) Depression()
Job stress()
Female production workers
6. Kim et al (2016) Lavender Direct and indirect
inhalation
Nonequivalent control
group/RCT
Korea 60 (exp: 30, cont: 30) -Quality of Sleep [QOS](+)
-[NRS])(+) [VSH](+)
-([NoA])(+)
Night shift nurse
7. Park et al (2010) Lavender, Vergamot, Basil exotic
2: 2: 1 (Mixed)
Direct and indirect
inhalation
Equivalent control
group
Korea 60 (exp: 30, cont: 30) Korea Sleep Scale A(+) Patients with
musculoskeletal pain
8. Choi et al (2016) Phytoncide Direct inhalation RCT Korea 34 (exp: 14, cont: 20) Korea Sleep Scale A(+) -College Life Stress()
-Feeling Scale L FS
University students
9. Lee et al (2011) Lavender Direct inhalation Nonequivalent control
group /RCT
Korea 67 (exp: 33, cont: 34) Korea Sleep Scale A(+) (State-Trait Anxiety Inventory()
Depression ()
Cesarean section mother
10. Lee (2018) Cymbopogon marini, Aniba
rosaeodora, Citrus bergamia
1: 1: 1 (Mixed)
Direct inhalation Nonequivalent control
Group /RCT
Korea 60 (exp: 30, cont: 30) -Quality of Sleep [QOS] (+) Japan Society for Occupational
Health (Fatique)()
Subway crew in shift work
11. Choi (2016) Grapefruit, Citrus paradisi,
Geranium, Neroli 4: 2: 3
(Mixed)
Direct inhalation RCT Korea 54 (exp: 27, cont: 27) -Quality of Sleep [QOS](+) (Synder
Halperm Verran: VHS)
VSH sleep scale(+)
-Visual analog scale: (VAS)(
NPY/ GLP-1
Overweight middle-aged
woman
12. Lee (2018) Lavender, Ylang-Ylang, Marjoram
4: 1: 5 (Mixed)
Direct inhalation/Indirect
inhalation
RCT Korea 62 (exp: 31, cont: 31) Verran & Synder-Halpern Sleep (+) -Subjective stress response
(NRS)()
-Physiological stress response()
A middle-aged woman
13. Lee (2018) Lavender, Ylang-Ylang, Neroli 4:
2: 1 (Mixed)
Direct inhalation RCT Korea 63 (exp: 31, cont: 32) -Quality of Sleep [QOS](+)
- NRS (Numeric Rating Scale)(+) -VSH
-(Actigraph[63])
-(Turbidimetric Immnuassay, TIA)
Stress()
-NRS (Numeric Rating Scale)
-Serum cortisol levels
Night shift nurse
14. Cho (2011) Lavender, Roman Chamomile,
Neroli
2: 1: 0.5 (Mixed)
Direct inhalation Non-equivalent control
group pretest-/RCT
Korea 56 (exp: 28, cont: 28) -VSH (Snyder-Halpern and Verran )
[46]
Sleep Scale
Anxiety
-(STAI-KYZ)
-Blood pressure
Patient with cardiac stent
intubation
15. Choi (2011) Roman Chamomile, Lavender,
Marjoram, Sandalwood
3: 2: 1: 1 (Mixed)
Direct inhalation Non-equivalent control
group /RCT
Korea 74 (exp: 37, cont: 37) Korea Sleep Scale A(+) Stress()
PWI(+)
Schizophrenic
16. Lee (2006) Lavender, Roman Chamomile
2: 1 (Mixed)
Direct inhalation/Indirect
inhalation
Nonequivalent control
Group/RCT
Korea 40 (exp: 20, cont: 20) -VSH(+) -Comfort
General comfort questionnnaire
-Anxiety ()
Patient with cardiac stent
intubation
17. Cho (2017) Lavender Direct inhalation Nonequivalent
control Group/RCT
Korea 60 (exp: 30, cont: 30) -VSH(+) -Subject Stress
-NRS()
- (Stress Index [S.I])
- (Blood pressure)
Clinical pulmonary infection
score
18. Lee (2016) Bergamot, Lavender, sweet
Majoram
1: 2: 1 (Mixed)
Direct inhalation/Indirect
inhalation
Nonequivalent control
group /RCT
Korea 40 (exp: 19, cont: 20) -VSH(+) -Fatique (Japan Society for
Occupational Health)
General
19. Min (2015) Korea 60 (exp: 30, cont: 30) -Quality of Sleep [QOS](+) Night shift nurse
(continued )
Cheong et al. Medicine (2021) 100:9 Medicine
10
Table 4
(continued).
Study (year) Aroma (single/mixed) Application Research design Nation Samplesize (n) Primary outcome Secondary outcome Subject character
Sweet Orange, Lavender,
Chamomile
Direct inhalation/Indirect
inhalation
Nonequivalent control
Group /RCT
-Fatigue (japan Society for
Occupational Health)
20. Kim (2008) Bergamot, Lavender, Ylang-
Ylang, 3: 3: 1 (Mixed)
Direct inhalation/Indirect
inhalation
Non-equivalent control
group /RCT
Korea 39 (exp: 18, cont: 18) -VSH(+)
-Sleep satisfaction (VAS)[66]()
-Anxiety () Coronary angiography
patients
21. So (2012) Lavender, Sweet Orange,
Meichang: 2: 1: 1 (Mixed)
Direct inhalation/Indirect
inhalation
Nonequivalent control
group/RCT
Korea 70 (exp: 35, cont: 35) Visual Analogue Scale: VAS() -Pain () (VisualAnalogue Scale:
VAS)
-Anxiety()
-Vitals signal
The paitients done colon
resection
22. Choi (2013) Lavender, Mandarin, Majoram
3: 2: 1 (Mixed)
Direct inhalation/Indirect
inhalation
Nonequivalent control
group/RCT
Korea 60 (exp: 30, cont: 30) -Korea Sleep Scale A(+)
-VAS()
-Pain()/-Stress ()
-Cotisol
-Index of nausea vomiting &
retching
Hysterectomy patient
23. Lee (2016) Chamomile, Sweet Orange
1: 2 (Mixed)
Direct inhalation/Indirect
inhalation
RCT Korea 53 (exp: 27, cont: 26) -VSH(+) -Pain() Pneumonectomy
24. Jeon (2014) Argan Oil, sweat almond oil
Lavender geranium,
Chamaecyparis obtusa
essence (not information)
Direct inhalation/Indirect
inhalation
RCT Korea 19 (exp: 12, cont: 7) -Korea Sleep Scale A(+)
-VAS()
-Depression() Middle women
25. Nam (2007) Lavender Direct inhalation/Indirect
inhalation
RCT Korea 36 (exp: 18, cont: 18) -Researcher devised sleep disorder
observation record ()
Problem behavior measurement
(Kim, 2003
[66]
)
26. Lillehei et al (2016) Lavender Direct inhalation RCT USA 76 (exp: 38, cont: 38) -PSQI (Pittsburgh Sleep Quality Index)
()
-Self Assessment of Change
Questionair (not.sig)
College students with sleep
problems
27. pouya Nematolahi
et al (2018)
Rosemary Direct inhalation RCT IRAN 68 (exp: 34, cont: 34) -PSQI (Pittsburgh Sleep Quality Index)
()
-HAS()
_HAD()
-Memory (not sig.)
General
28. Lee et al (2017) Lemon, eucalyptus, tea tree,
peppermint
4: 2: 2: 1 (Mixed)
Direct inhalation RCT Kor 60 (exp: 30, cont: 30) -QOS()
-time of sleep(+)
-Stress Index()
-Depression()
General
29. Mahnaz et al
(2015)
Lavender Direct inhalation RCT IRAN 158 (exp79, cont: 79) QOS
30. Lee (2004) Lavender, eucalyptus
Not information
Direct /Indirect
inhalation
RCT Kor 51 (exp25, cont: 26) QOS()
-SHV(+)/-VAS()
-Rhoten Fatique()
31. Ali, et al (2014) Rosa damascence Indirect inhalation RCT IRAN 60 (exp30, cont: 30) PSQI() Cardiac patients
32. Ezgi, et al (2017) Lavender Indirect inhalation RCT Turkey 60 (exp30, cont: 30) PSQI() -BAI() Sleep disorder and anxiety
patietns
33. Namni, et al
(2005)
Lavender Direct inhalation RCT USA 31 (exp16, cont: 15) Stanford Sleepiness Scale()
-The Profile of Mood State
Questionnaire()
General
34. Mahin, et al (2010) Lavender Direct inhalation RCT IRAN 64 (exp32, cont: 32) QOS() General
Cheong et al. Medicine (2021) 100:9 www.md-journal.com
11
The results are as follows: first, lavender was used as the
aromatic oil in most of the studies. In both types of studies that
used single aromatic oil and mixed oils, lavender was used most
widely used. As reported by studies,
[60,61]
lavender makes the
body feel heavy and provides a sense of stability, also, because of
its natural sedation, lavender balm is an example of Western folk
medicine that solves the problem of insomnia using a pillow filled
with lavender, which may be the reason for its usage in most
studies.
Additionally, the quality assessment of studies showed that
there was a high risk for performance and selection bias. This was
because specific descriptions of research subject assignment and
randomization were not described in the studies. Further studies
to correct for these biases are necessary. Moreover, unclear risk of
detection bias was observed; however, there was no specific
report on the blinding of outcome assessment. Thus, as
mentioned in previous studies, outcome assessment must be
conducted carefully on studies regarding aroma.
[17]
Second, the
meta-analysis results are as follows. No statistically significant
publication bias was observed in the studies. However, lavender
was used in most studies, as seen in the systematic review results.
This suggests that lavender may be the preferred aroma oil for
sleep; however, there may be differences in the commercially
available aroma.
[62]
Therefore, qualitative research on aroma-
therapists is recommended.
Analysis of effect size showed that the effect size of aroma
inhalation therapy in primary and secondary outcomes was
greater than the medium effect size, which indicates significant
outcomes. Additional analysis was performed to assess the
difference in effects by comparing the single and complex mixed
aromas. As a result, the effects of a single aroma were greater than
those of the mixed aroma. This finding is consistent with previous
Table 5
Effect size based on research duration of the time and times.
Variables KES (g) SE 95% CI PQ
B
(df)
Inhalation time
24 hours 32 0.476 0.060 0.358–0.594 .000 5.637 (1)
∗
Before sleep 139 0.661 0.049 0.564–0.758 .000
The number of aroma inhalation
1 104 0.699 0.059 0.583–0.816 .000 3.504 (2)
2 10 0.645 0.154 0.344–0.946 .000
3 25 0.534 0.073 0.390–0.678 .000
N ES (g) SE 95% CI P
Nation
Korea 25 0.724 0.071 0.586–0.863 .000 7.766
∗∗
(1)
the others 9 0.470 0.058 0.357–0.583 .000
CI =confidence interval; ES =effect sizes; K=the number of effect sizes; P=P-value; Q
B
=difference verification between groups; SE=standard error.
∗
P<.05.
∗∗
P<.01.
Figure 5. Forest plot of the aroma inhalation therapy.
Table 6
Result of the Trim and Fill.
Studies trimmed ES
c
95% CI Q
Observed values 0.64971 0.54224–0.75719 193.51456
Adjusted values 0 0.64971 0.54224–0.75719
CI =confidential interval; ES =effect sizes; K=the number of effect sizes; Q
B
=difference verification
between groups; SE =standard error.
Cheong et al. Medicine (2021) 100:9 Medicine
12
Table 7
Validation of the homogeneity and effect size of the primary outcomes.
Model N KES (g) U(%) 95% CI Q(df) I
2
Fixed 34 172 0.593 82.86 0.551–0.636 193.515(33) 82.947
∗∗
Random 34 172 0.650 84.05 0.542–0.757
CI =confidential interval; ES =effect sizes; K=the number of effect sizes; Q
B
=difference verification between groups; SE=standard error.
∗
P<.05.
∗∗
P<.01.
Table 8
The effect size of secondary outcomes.
Secondary outcomes K(%) ES (g) SE 95% CI PQ
B
(df)
Stress 30 0.838 0.154 0.535–1.140 .000 2.913(4)
Anxiety 10 0.599 0.138 0.328–0.869 .000
ETC (blood pressure, appetite, pain) 27 0.592 0.081 0.434–0.750 .000
Depression 6 0.556 0.116 0.329–0.783 .000
Fatigue 10 0.544 0.089 0.370–0.719 .000
CI =confidence interval; ES =effect sizes; K=the number of effect sizes; P=P-value; Q
B
=difference verification between groups; SE=standard error.
Table 9
The effect sizes of aroma types (single or mixed).
K(%) ES (g) SE 95% CI PQ
B
(df)
Single 59 (34.5%) 0.720
∗∗
0.081 0.561–0.879 .000 2.38
∗
(1)
Mixed 112 (65.5%) 0.576
∗∗
0.047 0.484–0.667 .000
CI =confidence interval; ES =effect sizes; K=the number of effect sizes, P=P-value, Q
B
=difference verification between groups, SE=standard error.
∗
P<.05.
∗∗
P<.01.
Table 10
Effect size based on types of study subjects (clinical group and general [shift workers and non-shift workers]).
K(%) ES (g) SE 95% CI PQ
B
(df)
Clinical group 60 0.782 0.083 0.620–0.944 .000 6.759 (1)
∗
General 111 0.538 0.044 0.452–0.624 .000
Non-night shift workers 76 0.483 0.039 0.407–0.559 .000 3.186 (1)
Night shift workers 35 0.682 0.104 0.477–0.886 .000
CI =confidence interval two dependent; ES=effect sizes; K=the number of effect sizes, Q
B
=difference verification between groups, SE=standard error.
∗
P<.05.
∗∗
P<.01.
Table 11
A regression analysis of the main effects and sub-effects of the aroma inhalation period.
SE –95% CI +95% CI Zt
2
b0.00367 0.00103 0.00166 0.00568 3.57951 0.13179
∗∗
Intercept 0.50136 0.04030 0.42237 0.58035 12.44002
b0.00405 0.00119 0.00173 0.00638 3.41241 0.24879
∗∗
Intercept 0.47506 0.04471 0.38743 0.56269 10.62532
CI =confidence interval; SE =standard error; Z =value of standard normal deviate.
∗
P<.05.
∗∗
P<.01.
∗∗∗
P<.001.
Cheong et al. Medicine (2021) 100:9 www.md-journal.com
13
Figure 6. The regression analysis of aroma therapy program according to years about for the slope of the primary outcome.
Founded studies Through a database
search
(n = 7,200 )
Screening Included Eligibility Identification
Additional records identified
through other sources
(n =724 )
Records after duplicates and articles unrelated
sleep problem removed (n =1,041)
Records screened
(n =361)
Records excluded
(n = 301)
Full-text articles assessed
for eligibility
(n = 60 )
Full-text articles excluded,
with reasons
(n =26)
Studies included in
qualitative synthesis
(n = 34 )
Studies included in
quantitative synthesis
(meta-analysis)
(n =34 )
Figure 7. The regression analysis of aroma therapy program according to years about for the slope of secondary outcome.
Cheong et al. Medicine (2021) 100:9 Medicine
14
reports,
[63]
indicating that a single aroma is more effective for
treating sleep problems. Moreover, the effects of aroma
inhalation were greater in those experiencing sleep disorders
compared with those that complained of general sleep problems.
This finding demonstrates that aroma inhalation therapy may
play a role as a complementary and alternative method. As a
result, it was estimated that aroma inhalation therapy would be
effective not only for sleep disorders but also for patients
suffering from various psycho-emotional disorders and severe
diseases such as cancer, in the same context as stated in previous
studies.
[64–66]
This study aimed to identify significantly greater
effects among aroma inhalation time and frequency, and the
following are the results of the analysis of aroma inhalation
methods. It was observed that the effects were the greatest before
falling asleep and that there was no difference in the frequency of
aroma inhalation. Thus, it is recommended that lavender oil be
used for direct inhalation before sleep to solve sleep problems in
the future.
The limitations of the current study are as follows. First, this
study was conducted on papers published until June 2019, and
studies published in 2020 were not included. This was done to
analyze the results of 10 years. Therefore, a meta-analysis
including papers published from late 2019 to the present of
2020 is recommended. Second, the method was limited to the
inhalation of aroma oils, and methods such as massage were
excluded. This w as to help those experiencing sl eep problems find
an effective self-method that is not restricted by time and place.
Therefore, future studies on the analysis of various intervention
methods using aroma in addition to inhalation methods are
recommended. Third, this study was only conducted on aroma
oils and therefore a comparative advantage analysis could not be
performed. Future studies that can conduct network meta-
analysis for comparative advantage analysis are recommended.
Fourth, lavender aroma oil was used in most of the selected
studies. It is highly likely that aroma experts and researchers
judged that the unique scent of lavender to be optimal for
providing mental and physical stability related to sleep.
However, the specific reason for the use of lavender could not
be addressed in the current study. Therefore, further qualitative
studies on the selection of lavender oil are necessary. Nonethe-
less, the findings of this study may be used as basic dat a to create a
program that will help reduce sleep problems using aroma oils in
the future.
5. Conclusion
The quality assessment of studies demonstrated a high risk of
performance bias and selection bias. Unclear risk of detection
bias was observed; however, there was no specific report on
blinding of assessment outcomes. Lavender was the most used
aroma oil related to sleep. The intervention method was mainly
direct inhalation and secondary outcomes such as stress, anxiety,
and depression were evaluated. Meta-analysis showed that the
effects of aroma inhalation therapy were significant in mediating
sleep problems. Additionally, the evaluation of secondary
outcomes showed that it had a significant effect size in reducing
the stress emotion, anxiety, and depression. In detail, aroma
inhalation therapy with single oil was more beneficial before
going to sleep for insomnia patients rather than those with
general sleep problems. Finally, primary and secondary outcome
analyses demonstrated that the effects increased significantly as
the number of therapy sessions increased.
Author contributions
Conceptualization: Moon Joo Cheong.
Data curation: Moon Joo Cheong, Hyung Won Kang.
Formal analysis: Moon Joo Cheong.
Investigation: Moon Joo Cheong.
Project administration: Moon Joo Cheong, Hyung Won Kang.
Resources: Moon Joo Cheong, Hyung Won Kang.
Supervision: Moon Joo Cheong, Hyung Won Kang.
Writing –original draft: Moon Joo Cheong, Hyung Won Kang.
Writing –review & editing: Moon Joo Cheong, Hyung Won
Kang, Sungchul Kim, Jee Su Kim, Byeonghyeon Jeon,
Hyeryun Lee, Yu Ra Lee, Yeoung-Su Lyu.
References
[1] Kyle SD, Morgan K, Espie CA. Insomnia and health-related quality of
life. Sleep Med Rev 2010;14:69–82.
[2] Smagula SF, Stone KL, Fabio A, et al. Risk factors for sleep disturbances
in older adults: evidence from prospective studies. Sleep Med Rev
2016;25:21–30.
[3] Hwang E, Shin S. The effects of aromatherapy on sleep improvement: a
systematic literature review and meta-analysis. J Altern Complement
Med 2015;21:61–8.
[4] Wanniarachige D, Murphy S, Titiloye A, et al. GP172 Should healthcare
professionals routinely recommend a commercially available sleep
movement monitor for babies? Arch Dis Child 2019;104:A99–100.
[5] Chan WS, Levsen MP, McCrae CS. A meta-analysis of associations
between obesity and insomnia diagnosis and symptoms. Sleep Med Rev
2018;40:170–82.
[6] Herron K, Farquharson L, Wroe A, et al. Development and evaluation of
a cognitive behavioural intervention for chronic post-stroke insomnia.
Behav Cogn Psychother 2018;46:641–60.
[7] Galinsky AM, Ward BW, Joestl SS, et al. Sleep duration, sleep quality,
and sexual orientation: findings from the 2013–2015 National Health
Interview Survey. Sleep Health 2018;4:56–62.
[8] Mendelson WB. A review of the evidence for the efficacy and safety of
trazodone in insomnia. J Clin Psychiatry 2005;66:469–76.
[9] Winbush NY, Gross CR, Kreitzer MJ. The effects of mindfulness-based
stress reduction on sleep disturbance: a systematic review. Explore (NY)
2007;3:585–91.
[10] Lee JT, Lee KJ, Park JB, et al. The Relations between Shiftwork and Sleep
Disturbance in a University Hospital Nurses. Korean J Occup Environ
Med 2007;19:223–30.
[11] Yang EK, Choi IR, Kim SM. The impact of sleep disorder and job stress
on turnover intention of shift-working nurses. Korean J Stress Res
2017;25:255–64.
[12] Kim KS. Effects of subway workers’night working on metabolic
syndrome. Ann Occup Environ Med 2016;11:413–4.
[13] Lee H, Lim YJ, Jung HY, et al. Sleep disturbance, physical activity and
health related quality of life in patients with chronic obstructive
pulmonary disease. J Korean Gerontol Soc 2011;31:607–21.
[14] Park YJ, Kim YS. A convergence study of depression, health-related
quality of life and sleep disturbance according to the level of physical
activity of hemodialysis patients. J Digit Converg 2018;16:345–55.
[15] Jung J, Lee EH, Yang YJ, et al. Sleep pattern and factors causing sleep
disturbance in adolescents with cancer before and after hospital
admission. Asian Oncol Nurs 2017;17:143–50.
[16] Kim SJ, Na H. A study of the relationships between compassion fatigue,
compassion satisfaction, depression, anxiety, and sleep disorders among
oncology nurses. Asian Oncol Nurs 2017;17:116–23.
[17] Koo BS, Park KS, Ha JH, et al. Inhibitory effects of the fragrance
inhalation of essential oil from Acorus gramineus on central nervous
system. Biol Pharm Bull 2003;26:978–82.
[18] Moher D, Liberati A, Tetzlaff J, et al. PRISMA GroupPre ferred reporting
items for systematic reviews and meta-analyses: the PRISMA statement
[published correction appears in Int J Surg. 2010;8(8):658]. Int J Surg
2010;8:336–41.
[19] Shojania KG, Sampson M, Ansari MT, et al. How quickly do systematic
reviews go out of date? A survival analysis. Ann Intern Med 2007;
147:224–33.
[20] Lichstein KL, Stone KC, Donaldson J, et al. Actigraphy validation with
insomnia. Sleep 2006;29:232–9.
Cheong et al. Medicine (2021) 100:9 www.md-journal.com
15
[21] Roland PS, Rosenfeld RM, Brooks LJ, et al. Clinical practice guideline:
polysomnography for sleep-disordered breathing prior to tonsillectomy
in children. Otolaryngol Head Neck Surg 2011;145(1 suppl):S1–5.
[22] Carney CE, Buysse DJ, Ancoli-Israel S, et al. The consensus sleep diary:
standardizing prospective sleep self-monitoring. Sleep 2012;35:287–302.
[23] Haythornthwaite JA, Hegel MT, Kerns RD. Development of a sleep diary
for chronic pain patients. J Pain Symptom Manage 1991;6:65–72.
[24] MacFarlane JG, Cleghorn JM, Brown GM, et al. The effects of
exogenous melatonin on the total sleep time and daytime alertness of
chronic insomniacs: a preliminary study. Biol Psychiatry 1991;30:371–6.
[25] Buysse DJ, Ancoli-Israel S, Edinger JD, et al. Recommendations for a
standard research assessment of insomnia [published correction appears
in Sleep. 2006 Nov 1;29(11):1380]. Sleep 2006;29:1155–73.
[26] Haynes SN, Adams A, Franzen M. The effects of presleep stress on sleep-
onset insomnia. J Abnorm Psychol 1981;90:601–6.
[27] Gross RT, Borkovec TD. Effects of a cognitive intrusion manipulation on
the sleep-onset latency of good sleepers. Behav Ther 1982;13:112–6.
[28] Wilson DL, Barnes M, Ellett L, et al. Decreased sleep efficiency, increased
wake after sleep onset and increased cortical arousals in late pregnancy.
Aust N Z J Obstet Gynaecol 2011;51:38–46.
[29] Buysse DJ, Reynolds CF3rd, Monk TH, et al. The Pittsburgh Sleep
Quality Index: a new instrument for psychiatric practice and research.
Psychiatry Res 1989;28:193–213.
[30] Monk TH, Reynolds CF, Kupfer DJ, et al. The Pittsburgh sleep diary. J
Sleep Res 1994;3:111–20.
[31] Kim JH. Types of mindfulness meditation and their implications for
cognitive behavioral therapy. Cogn Behav Pract 2004;4:27–44.
[32] Hays RD, Martin SA, Sesti AM, et al. Psychometric properties of the
Medical Outcomes Study Sleep measure. Sleep Med 2005;6:41–4.
[33] Lee BK. The effects of mindfulness-based stress reduction (MBSR)
program on pain and anxiety in cancer patients. Korean J Stress Res
2013;21:263–74.
[34] Krouse HJ, Davis JE, Krouse JH. Immune mediators in allergic rhinitis
and sleep. Otolaryngol Head Neck Surg 2002;126:607–13.
[35] Shahid A, Wilkinson K, Marcu S, Shapiro CM. Women’s Health
Initiative Insomnia Rating Scale (WHIIRS). S.T.O.P., T.H.A.T., One
Hundred Other Sleep, Scales New York, NY: Springer; 2011. 403–404.
[36] Oh JJ, Song MS, Kim SM. Development and validation of Korea sleep
scale A. J Korean Acad Nurs 1998;28:563–72.
[37] Bech P, Allerup P, Gram LF, et al. The Hamilton depression scale.
Evaluation of objectivity using logistic models. Acta Psychiatr Scand
1981;63:290–9.
[38] Beck AT, Steer RA, Brown GK, et al. Beck depression inventory-II. San
Antonio 1996;78:490–8.
[39] Cohen S, Kamarck T, Mermelstein R. Perceived stress scale. Measuring
Stress 1994;10:1–2.
[40] Remor E. Psychometric properties of a European Spanish version of the
Perceived Stress Scale (PSS). Span J Psychol 2006;9:86–93.
[41] Spielberger CD. State-trait anxiety inventory. The Corsini Encyclopedia
of Psychology 2010;1–11.
[42] Servaes P, Verhagen C, Bleijenberg G. Fatigue in cancer patients during
and after treatment: prevalence, correlates and interventions. Eur J
Cancer 2002;38:27–43.
[43] Lillehei AS, Halcon LL. A systematic review of the effect of inhaled
essential oils on sleep. J Altern Complement Med 2014;20:441–51.
[44] Higgins JP, Thomas J, Chandler J, et al. Cochrane Handbook for
Systematic Reviews of Interventions. John Wiley & Sons, 2019; 25–32.
[45] Hedges LV, Olkin I. Statistical Methods for Meta-analysis. Academic
Press, 2014.
[46] Snyder-Halpern R, Verran JA. Instrumentation to describe subjective
sleep characteristics in healthy subjects. Res Nurs Health 1987;10:
155–63.
[47] Littell JH, Corcoran J, Pillai V. Systematic Reviews and Meta-analysis.
Oxford University Press, 2008.
[48] Duval S, Tweedie R. Trim and fill: a simple funnel-plot-based method of
testing and adjusting for publication bias in meta-analysis. Biometrics
2000;56:455–63.
[49] Higgins JP, Green S. Cochrane handbook for systematic reviews. The
Cochrane Collaboration, vol. 5 West Sussex, England: John Wiley &
Sons Ltd.; 2008.
[50] Rosenthal R, Rubin DB. Statistical analysis: summarizing evidence versus
establishing facts. Psychol Bull 1985;97:527–9.
[51] Cohen J. Statistical Power Analysis for the Behavioral Sciences. Hillsdale,
NJ: Lawrence Earlbam Associates; 1988. 77–83.
[52] Wolf FM. Meta-analysis: Quantitative Methods for Research Synthesis.
Sage, 1986.
[53] Rosenthal R, Cooper H, Hedges L. Parametric measures of effect size.
Handb Res Synth 1994;621:231–44.
[54] Drake CL, Roehrs T, Roth T. Insomnia causes, consequences, and
therapeutics: an overview. Depress Anxiety 2003;18:163–76.
[55] Wang MY, Wang SY, Tsai PS. Cognitive behavioural therapy
for primary insomnia: a systematic review. J Adv Nurs 2005;50:
553–64.
[56] Smolensky MH, Di Milia L, Ohayon MM, et al. Sleep disorders, medical
conditions, and road accident risk. Accid Anal Prev 2011;43:533–48.
[57] Kamel NS, Gammack JK. Insomnia in the elderly: cause, approach, and
treatment. Am J Med 2006;119:463–9.
[58] Martin RA, Ford T. The Psychology of Humor: An Integrative
Approach. Academic Press, 2018; 25–26.
[59] Yoshiyama K, Arita H, Suzuki J. The effect of aroma hand massage
therapy for people with dementia. J Altern Complement Med 2015;
21:759–65.
[60] Buchbauer G, Jirovetz L, Jäger W, et al. Aromatherapy: evidence for
sedative effects of the essential oil of lavender after inhalation. Z
Naturforsch C J Biosci 1991;46:1067–72.
[61] Cavanagh HM, Wilkinson JM. Lavender essential oil: a review. Aust
Infect Control 2005;10:35–7.
[62] Toda M, Morimoto K. Evaluation of effects of lavender and peppermint
aromatherapy using sensitive salivary endocrinological stress markers.
Stress Health 2011;27:430–5.
[63] S¸entürk A, Tekinsoy Kartın P. The effect of lavender oil application via
inhalation pathway on hemodialysis patients’anxiety level and sleep
quality. Holist Nurs Pract 2018;32:324–35.
[64] Bilia AR, Guccione C, Isacchi B, et al. Essential oils loaded in
nanosystems: a developing strategy for a successful therapeutic
approach. Evid Based Complement Alternat Med 2014;2014:
6515931–14.
[65] Tisserand R, Young R. Essential Oil Safety-e-book: A Guide
for Health Care Professionals. Elsevier Health Sciences, 2013;
20–75.
[66] Cheong MJ, Lee GE, Kang HW, et al. Clinical effects of mindfulness
meditation and cognitive behavioral therapy standardized for insomnia:
a protocol for a systematic review and meta-analysis. Medicine (Madr)
2018;97:e13499:1–7.
Cheong et al. Medicine (2021) 100:9 Medicine
16