aromatherapy for treatment of hypertension a systematic review.pdf

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Aromatherapy for treatment of hypertension:

a systematic reviewjep_1521 37..41

Myung-Haeng Hur RN PhD,1 Myeong Soo Lee PhD,2 Chan Kim MD PhD3 and

Edzard Ernst MD PhD FMedSci FSB FRCP FRCPEd4

1Professor, School of Nursing, Eulji University, Daejeon, South Korea2Principal Researcher, Division of Standard Research, Korea Institute of Oriental Medicine, Daejeon, South Korea and Honorary University Fellow,

Complementary Medicine, Peninsula Medical School, University of Exeter, Exeter, UK3Professor, Department of Physiology and Biophysics, School of Medicine, Eulji University, Daejeon, South Korea4Laing Chair in Complementary Medicine, Director and Professor, Complementary Medicine, Peninsula Medical School, University of Exeter,

Exeter, UK

Keywords

aromatherapy, hypertension, systematic

review

Correspondence

Dr Myeong Soo Lee

Division of Standard Research

Korea Institute of Oriental Medicine

Daejeon 305 811

South Korea

E-mail: [email protected];

[email protected]

Accepted for publication: 10 May 2010

doi:10.1111/j.1365-2753.2010.01521.x

AbstractObjectives The objective of this review is to systematically review the evidence for the

effectiveness of aromatherapy in the treatment of high blood pressure.

Methods Twelve databases were searched from their inception through December 2009.

Controlled trials testing aromatherapy in patients with hypertension of any origin that

assessed blood pressure were considered. The selection of studies, data extraction and

validations were performed independently by two reviewers.

Results One randomized clinical trial (RCT) and four non-randomized controlled clinical

trials (CCTs) met our inclusion criteria. The one RCT included tested the effects of

aromatherapy as compared with placebo and showed significant reduction of systolic blood

pressure and diastolic blood pressure. All of the four CCTs showed favourable effects of

aromatherapy. However, all of the CCTs also had a high risk of bias.

Conclusion The existing trial evidence does not show convincingly that aromatherapy is

effective for hypertension. Future studies should be of high quality with a particular

emphasis on designing an adequate control intervention.

Introduction

High blood pressure (BP) is a major, independent risk factor for

cardiovascular disease (CVD). Many cardiovascular events would

be preventable if cardiovascular risk factors could be eliminated

[1]. Complementary therapies are popular and frequently used by

patients with CVD[2]. Many complementary therapy options exist,

and more than 95 different complementary therapies have been

recommended for hypertension [3]. Aromatherapy is one option.

Aromatherapy is the therapeutic use of essential oils fromplants [4]. Essential oils can be absorbed into the body via the

skin or the olfactory system. Many studies have found that olfac-

tory stimulation produces immediate changes in physiological

parameters such as blood pressure (BP), muscle tension, pupil

dilation, skin temperature, pulse rate and brain activity [47].

Clients and practitioners of aromatherapy perceive such treat-

ments to be effective, but physicians are often sceptical of this

claim. Several textbooks have also asserted the favourable thera-

peutic effects of aromatherapy for CVDs including hypertension

[810]. However, no systematic reviews for this condition are

currently available.

The aim of this systematic review was to summarize and criti-

cally assess the evidence from controlled clinical trials for or

against the effectiveness of aromatherapy as an anti-hypertensive

treatment.

Methods

Data sources

The following electronic databases were searched from theirinception up to December 2009: Medline, CINAHL, EMBASE,

PsycInfo, The Cochrane Library 2009 (Issue 4), 6 Korean Medical

Databases (Korean Studies Information, DBPIA, Korea Institute

of Science and Technology Information, Research Information

Center for Health Database, KoreaMed, National Assembly

Library), and Chinese Medical Database (CNKI), as well as three

Japanese electronic databases (Japan Science and Technology

Information Aggregator Electronic, Journal@rchive and Science

Link Japan). The search phrase used was ([aromatherapy OR

aroma*] AND [blood pressure OR hypertension]). We also manu-

ally searched our departmental files and relevant journals, FACT

Journal of Evaluation in Clinical Practice ISSN 1365-2753

2010 Blackwell Publishing Ltd, Journal of Evaluation in Clinical Practice18 (2012) 3741 37


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(Focus on Alternative and Complementary Therapies) and For-

schende Komplementrmedizin und Klassische Naturheilkunde

(Research in Complementary and Classical Natural Medicine), up

to December 2009. In addition, the references in all articles studied

were manually searched for additional relevant articles.

Study selectionAll prospective randomized clinical trials (RCTs) and non-

randomized controlled clinical trials (CCTs) were included if the

patient population included those with hypertension who received

aromatherapy alone or combined with other treatments. Trials with

designs that did not allow for an evaluation of the effectiveness of

the intervention (e.g. by using treatments of unproven efficacy in

the control group or comparing two different forms of aroma-

therapy) were excluded. Dissertations and abstracts were included.

Uncontrolled studies, case series and case reports were excluded.

Data extraction and assessment of the

risk of bias

Hard copies of all articles were obtained and read in full by two

independent reviewers (MHH, MSL). Data from the articles were

validated and extracted according to pre-defined criteria (Table 1).

The risk of bias was assessed using the Cochrane classification as

represented by four criteria [11]: sequence generation, incomplete

outcome measures, blinding and allocation concealment. Discrep-

ancies were resolved through discussion between two reviewers

(MHH, MSL) and, if needed, by seeking the opinion of a third

reviewer (EE). There were no disagreements between the three

reviews regarding the assessment of the risk of bias.

Results

The searches identified 74 potentially relevant studies, five ofwhich met our inclusion criteria (Fig. 1). The key data are sum-

marized in Table 1 [1216]. A total of 200 participants were

included in these trials. Four trials originated from Korea [1215],

and one study was conducted in the UK [16]. Four trials [1215]

used aromatherapy as inhalation or local topical treatment, and

the other [16] used aromatherapy with massage. The number of

aromatherapy sessions ranged from 1 to 28. The session duration

ranged from 2 minutes to 45 minutes. Three [1416] of the

included trials adopted a two-armed parallel-group design and one

[13] a three-armed parallel group design, whereas the other [12]

used a cross-over design.

Study quality

Among the included trials, most had a high risk of bias. One

RCT reported sequence generation and used patient blinding [12].

The others also had a potential high risk of bias, despite the

employment of patient blinding by two CCTs [12,13].

Outcomes

Aromatherapy versus placebo treatment

Two trials [12,13] compared the effect of aromatherapy as com-

pared with placebo treatment on BP values in pre-hypertension

middle-aged women or essential hypertension patients. One RCT

[12] showed significant reduction of systolic blood pressure (SBP)

and diastolic blood pressure (DBP) in the aromatherapy group as

compared with the placebo group. The other CCT also reported

favourable effects of aromatherapy as compared with placebo

on the reduction of SBP and DBP [13]. One RCT [12] reported

significant changes in epinephrine (E) and norepinephrine (NE)

elicited by aromatherapy as compared with placebo, whereas the

CCT [13] failed to do so.

Aromatherapy versus no treatment

Three CCTs tested aromatherapy as compared with no treat-

ment on BP in patients with essential hypertension [1315]. Two

CCTs [13,15] reported favourable effects of aromatherapy as

compared with no treatment on the reduction of SBP and DBP,

whereas the other CCT [14] did not report any such inter-group

difference.

Aromatherapy plus massage versus placeboplus massage

One CCT [16] tested aromatherapy massage as compared with

placebo plus massage on BP. Both treatments improved BP read-

ings. However, the details of these results were not reported.

Discussion

To the best of our knowledge, this is the first systematic review

of the effectiveness of aromatherapy for high blood pressure.

The results suggest that aromatherapy is more effective than

placebo in reducing SBP and DBP. However, the existing trial

evidence does not show convincingly that aromatherapy is effec-

tive in reducing blood pressure due to numerous drawbacks ofthe primary studies. .

The quality of the included studies was assessed based on the

descriptions of sequence generation, blinding, incompleteness of

outcome measures and allocation concealment. Among the five

studies that we included, only one [12] was randomized. The rest

were open to selection bias, which can generate false-positive

findings. Two studies [12,14] were published in a thesis, which had

not gone through the formal peer review process. Furthermore,

two CCTs failed to report the detailed results of statistical analysis

[14,16]. All of the studies were burdened with a high risk of bias.

Thus, the reliability of the evidence presented is clearly limited.

The mechanisms by which aromatherapy reduced BP may be

related to sympathetic nervous system (SNS) modulation. Aroma-therapy lowered the level of NE and E. This effect is compatible

with suppression of SNS activity as NE and E have been directly

linked to SNS [17]. However, more basic research is needed

to fully understand the mechanisms underlying the effects of

aromatherapy.

The next question that arises concerns the safety of aroma-

therapy. None of the reviewed studies reported any adverse events

related with aromatherapy. Aromatherapy appears to be generally

safe, and serious adverse effects have not been reported. Adverse

effects were not the focus of this review; regardless, the safety of

aromatherapy requires further research.

Aromatherapy for hypertension M-H. Hur et al.

2010 Blackwell Publishing Ltd38


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The limitations of our systematic review and any systematic

review in general pertain to the potential incompleteness of the

evidence reviewed. We aimed to identify all controlled clinical

trials on the topic. The distorting effects on systematic reviews and

meta-analyses arising from publication bias and location bias are

well documented [18,19]. In this review, there were no restrictions

in terms of publication language, and many different databases

were queried. We are confident that our search strategy located all

of the relevant data; however, a degree of uncertainty remains.

Moreover, selective publishing and reporting can be major causes

of bias. It is conceivable that several negative RCTs remain unpub-

lished, thus distorting the overall picture. Another possible source

of bias is the fact that most of the included trials were carried outin Korea, regions that have been shown to produce almost no

negative studies [20]. Further limitations of our review are the

potentially poor quality of the primary data and poor reporting of

results, which were highly heterogeneous in virtually every

respect. To establish the role of aromatherapy in the management

of hypertension patients, adequately designed trials are required.

Collectively, the existing trial evidence is not convincing

and does not show aromatherapy to be an effective modality for

managing hypertension. Future studies should be of high quality,

with a particular emphasis on designing adequate and appropriate

control groups.

Acknowledgement

This work was supported by Mid-career Researcher Program

through NRF Grant funded by MEST (No. 2009-0083800).

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Publications identified (n=74)

Publications excluded after screening the title and

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Reasons: Not related to aromatherapy (n=5)

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Figure 1 F lo w chart of tri al sel ecti on

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