DEPRESSION AND ANXIETY 29:545–562 (2012)
ReviewMEDITATIVE THERAPIES FOR REDUCING ANXIETY:
A SYSTEMATIC REVIEW AND META-ANALYSIS OFRANDOMIZED CONTROLLED TRIALS
Kevin W. Chen, MPH, Ph.D.,1,2∗ Christine C. Berger, Ph.D.,1 Eric Manheimer, M.S.,1 Darlene Forde, M.A.,1Jessica Magidson, M.S.,2 Laya Dachman, B.A.,2 and C. W. Lejuez, Ph.D2
Background: Anxiety disorders are among the most common psychiatric dis-orders and meditative therapies are frequently sought by patients with anxietyas a complementary therapy. Although multiple reviews exist on the generalhealth benefits of meditation, no review has focused on the efficacy of medita-tion for anxiety specifically. Methods: Major medical databases were searchedthoroughly with keywords related to various types of meditation and anxiety.Over 1,000 abstracts were screened, and 200+ full articles were reviewed.Only randomized controlled trials (RCTs) were included. The Boutron (Boutronet al., 2005: J Clin Epidemiol 58:1233–1240) checklist to evaluate a report of anonpharmaceutical trial (CLEAR-NPT) was used to assess study quality; 90% ofthe authors were contacted for additional information. Review Manager 5 wasused for meta-analysis. Results: A total of 36 RCTs were included in the meta-analysis (2,466 observations). Most RCTs were conducted among patients withanxiety as a secondary concern. The study quality ranged from 0.3 to 1.0 on the0.0–1.0 scale (mean = 0.72). Standardized mean difference (SMD) was –0.52 incomparison with waiting-list control (p < .001; 25 RCTs), –0.59 in comparisonwith attention control (p < .001; seven RCTs), and –0.27 in comparison withalternative treatments (p < .01; 10 RCTs). Twenty-five studies reported statisti-cally superior outcomes in the meditation group compared to control. No adverseeffects were reported. Conclusions: This review demonstrates some efficacy ofmeditative therapies in reducing anxiety symptoms, which has important clinicalimplications for applying meditative techniques in treating anxiety. However,most studies measured only improvement in anxiety symptoms, but not anxietydisorders as clinically diagnosed. Depression and Anxiety 29:545–562, 2012.C© 2012 Wiley Periodicals, Inc.
Key words: meditation; meditative therapies; anxiety; systematic review; meta-analysis
1Center for Integrative Medicine, University of MarylandSchool of Medicine, Baltimore, Maryland2Center for Addictions, Personality & Emotion Research, De-partment of Psychology, University of Maryland College Park,College Park, Maryland
∗Correspondence to: Kevin W. Chen, Center for IntegrativeMedicine, University of Maryland School of Medicine, 520 W. Lom-bard St. East Hall, Baltimore, MD 21201. E-mail: [email protected] for publication 31 October 2011; Revised 13 April 2012;Accepted 28 April 2012
DOI 10.1002/da.21964Published online 14 June 2012 in Wiley Online Library (wileyon-linelibrary.com).
BACKGROUNDDESCRIPTION OF THE CONDITION
In a given year, approximately 40 million Americanadults meet criteria for an anxiety disorder.[1] Althoughpharmacological approaches and more traditional formsof psychotherapy have strong empirical support for re-ducing anxiety, many patients are turning to meditationas an alternative approach to reduce stress and anxi-ety for a few key reasons. Meditation offers a therapeu-tic and often spiritual approach that avoids side effectsof medications, the stigma of psychiatric treatments, aswell as barriers related to issues of cost and accessibi-lity.[2–6]
C© 2012 Wiley Periodicals, Inc.
546 Chen et al.
MEDITATION: A DEFINITION AND ANOVERVIEW OF ITS BENEFITS
Meditation can be defined to include any of a family ofpractices in which the practitioner trains an individual toconsciously calm his/her mind in order to realize somebenefit or achieve inner peace or harmony. Despite lackof consensus in the scientific literature on a definitionof meditation, most researchers agree that meditationimplies a form of mental training that requires eitherstilling or emptying the mind, and its goal is to achieve astate of “detached observation” or “restful alertness.”[7]
The foundation of meditation practice is rooted in theprinciples of “self-observation of immediate psychic ac-tivity, training one’s level of awareness, and cultivat-ing an attitude of acceptance of process rather thancontent.”[6]
From the perspective of traditional Chinese medicine(TCM), all forms of meditation that are essentially mind-body integrative exercises are categorized as “qigong”.Qigong is defined as “the skill of mind–body exercisesthat integrate body, breath, and mind adjustments intoone,”[8] which addresses both psychological and phys-iological aspects of health. Although qigong has bothdynamic (movement) and static forms, the meditativestate—body, breath, and mind into one—is commonamong all of them. Given a lack of consensus in West-ern psychology about the definition of meditation andexactly what techniques it includes, in this review we usethe established definition of meditative therapies in Chi-nese medicine. Specifically, we include all mind–bodyexercises, both dynamic (moving) form and static (still)form, which aim to integrate breath–body–mind adjust-ments into one. As a result, this includes all meditations,yoga, mindfulness training, Transcendental Meditation(TM), qigong, tai chi (or Taiji), and even guided imagery,as guided imagery is an ancient technique in meditationpractice.[8]
Numerous reviews have been conducted evaluatingthe physical and psychological effects of meditation prac-tice on health [e.g.6, 9–12]. The majority of these reviewsillustrated a positive trend and/or health benefits, al-though their results were often inconclusive due to re-search design and sample limitations. More recently,Ospina et al.[6] conducted a large and thorough sys-tematic review on meditation practices for health(from 813 predominantly peer-reviewed studies). Theyidentified five broad categories of meditation prac-tice (mantra meditation, mindfulness meditation [MM],yoga, qigong, and tai chi) and reviewed the clinicalevidence for these practices for three important andcommon health-related conditions: hypertension, othercardiovascular diseases, and substance abuse. Theirmeta-analyses of 55 studies indicated that meditationpractices suggested some clinical changes and possiblypositive outcomes in healthy participants, but no conclu-sions were drawn from these studies on the clear clinicalbenefits of meditation.
Despite the noted beneficial trend of meditation prac-tices according to the Ospina’s review,[6] the effect ofmeditation on anxiety was only relevant to those with acardiovascular condition. Additionally, the other reviewsfocused on examining the effects of meditation on stressand related symptoms[13, 14] suggested a positive stressmanagement function of meditation practice. However,these studies have not examined effects on clinically rele-vant anxiety symptoms per se, or anxiety disorders morespecifically. Examining the effect of meditative thera-pies on anxiety outcomes has important clinical impli-cations, particularly in considering how we can improveanxiety outcomes using an approach that may improveaccess and tolerability of treatment in a range of clinicalsettings.
CONCEPTUAL FRAMEWORK OF MEDITATIONEFFECTS ON ANXIETY
In conceptualizing meditation’s impact on anxiety, itis important to consider this relationship in light of exist-ing biological, behavioral, and cognitive frameworks ofanxiety. For instance, prominent biological theories suchas the false suffocation alarm[15] and hyperventilation[16]
theories focus on the role of respiratory abnormalitiesin anxiety. From a learning perspective, anxiety and fearare a product of classical conditioning where a previouslynovel and innocuous stimulus has come to elicit an aver-sive, conditioned response due to the previous pairingof that stimulus with an anxiety/fear-relevant uncondi-tioned stimulus. Finally, from a cognitive perspective,people with anxiety disorders may be prone to overesti-mate danger and its potential consequences (e.g.[17]).
Considering the combined impact of biological, be-havioral, and cognitive vulnerabilities to anxiety, thereare several clear ways in which the role of meditationin the management of anxiety is quite clear. Addressingbiological vulnerability, meditation and related breathtraining can reverse abnormalities and alter the anx-iogenic effects of biological challenges.[18, 19] Indeed,a rich literature on abdominal breathing, commonlyused in meditation, has been used as a tool for cop-ing directly with panic attacks.[20, 21] Moreover, at aneurobiological level, meditation has consistently beenshown to reduce cortisol and catecholamine level (suchas epinephrine and norepinephrine) that may other-wise trigger biologically based anxiety responses.[22–24]
In line with Wolpe’s work on reciprocal inhibition (i.e.inhibiting anxiety by conditioning a feeling or responsethat is not compatible with the feeling of anxiety in itsplace[25]), meditation may address behavioral vulnera-bility when conducted in the context of the conditionedstimulus. In this way, meditation is then serving to cre-ate a newly conditioned response, thereby resulting inthe “extinction” of the anxious/fear-related conditionedresponse. Finally, meditation may address cognitive vul-nerability by using meditative skills to help the practi-tioner remain “detached” yet not avoidant to address the
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Review: Meditative Therapies for Reducing Anxiety 547
cognitive misattributions accompanying anxiety as a sub-stitute for avoidance. In other words, meditation canserve as a training to control the mind as a means to re-duce anxiety as well as to develop a helpful coping mech-anism to facilitate a calm and nondestructive responseto stress and strain. Interestingly, these three compo-nents of a conceptual framework of anxiety—biological,behavioral, and cognitive—correspond to the three ad-justments or regulations used in defining the medita-tive therapies—the adjustments of breathing, body, andmind.
LIMITATIONS OF PREVIOUS REVIEWSDespite the absence of a systematic review focusing on
anxiety, there are numerous reports suggesting the po-tential benefits of meditation in reducing anxiety.[26–28]
Studies have examined the effects of meditative ther-apies on both stress and anxiety, primarily MM[29–32]
and yoga,[33–35] which largely have demonstrated posi-tive outcomes on anxiety. However, to date, efforts tosynthesize evidence pertaining to the efficacy of medi-tative therapies on anxiety have been very limited. Thisnext step in synthesizing the literature is necessary to in-form our clinical understanding of which aspects of med-itative therapies are most efficacious for anxiety specifi-cally.
Existing efforts to examine the efficacy of meditationfor anxiety specifically have been scarce and limited ina few distinct ways. A Cochrane review on “meditationtherapy for anxiety disorders”[10] identified only two el-igible randomized controlled trials (RCTs), primarilybecause many studies have not focused on meditationfor treating clinically relevant anxiety symptoms and/ordisorders specifically. Indeed, an inspection of the lit-erature reveals that most studies on meditative thera-pies, especially the high-quality RCTs, include anxietyas a symptom or one of the multiple outcomes, but notas a primary outcome, which may explain their omis-sion from existing systematic reviews. Further, the smallnumber of studies included in previous reviews (e.g. ofKrisanaprakornkit[10]) did not permit any conclusions tobe drawn, suggesting a systematic review with more in-clusive meditation and anxiety symptoms is needed onthis topic.
In addition, most reviews to date focus on one typeof meditation only, such as yoga,[36] MM,[26,37, 38], ortai chi.[39] These reviews typically included only a smallnumber of qualified studies, often with low quality ac-cording to traditional review criteria, which also do notpermit conclusions to be drawn. Finally, the majority ofexisting reviews have applied evaluation criteria based onpharmaceutical RCTs that tended to underestimate theactual quality of these studies, since some of these tra-ditional criteria for quality assessment may not apply tothe study of meditative therapies (e.g. blindness, typicallyused in pharmaceutical trials, may not be applicable tomeditation trials, in which blindness of the participantsor provider cannot be assured).
IMPORTANCE OF THE CURRENT REVIEWConducting a more thorough systematic review of
the meditative therapies for reducing anxiety symptomsis an important next step, given that many meditativeapproaches overlap in terms of their effects, and manysimilar mind–body practices that we term “meditativetherapies” may also have an effect on anxiety, but theirefficacy has not yet been fully reviewed. The current re-view aimed to investigate all therapies under the rubric of“meditative,” which will all be called qigong or medita-tive therapy in China (such as yoga, MM, TM, qigong, taichi or Taiji, and guided imagery)1 to examine their effectson anxiety using more appropriate criteria for qualityassessment. The objective of this review was to system-atically investigate the evidence on the overall efficacy,effect size, and safety of all meditative therapies for re-ducing anxiety symptoms across various types of partici-pants and health conditions in RCTs to guide cliniciansand future research in this area.
METHODSLITERATURE RESEARCH
A thorough literature search was independently carried out bythe reviewers through December 2010 using the following databases:Pubmed, PsychINFO, Embase, Cochrane Central Register of Con-trolled Trials, and Qigong database (by Qigong Institute;[40]). Thekeywords used in the search included a combination of diagnostic oranxiety measures (such as anxiety, anxious, phobic, panic, obsessive-compulsive disorder (OCD), social phobia, post-traumatic stressdisorder (PTSD), stress disorder, neurosis or neurotic) and ameditation-related intervention (such as meditation, mindfulness,mindfulness-based stress reduction (MBSR), meditative, Vipassana,Zen, yoga, yogic, pranayama, Kriya, Qigong, chi kung, Tai Chi, Taiji,Kundalini, Reiki, Prana, TM, and guided imagery). Previously pub-lished reviews of meditation for stress and other health issues werealso carefully screened to pick up missed clinical studies with anxietyas secondary outcomes.
STUDY ELIGIBILITYTwo reviewers screened the abstracts of all publications obtained by
the search strategies. Studies meeting the following inclusion criteriawere selected for further review: (1) prospective RCTs with meditativetechnique used as intervention; (2) anxiety or related diagnosis wasone of the outcomes with a psychometric measure; (3) total numberof randomized subjects greater than 20 (N ≥ 20) with a control groupeither inactive (waiting list) or active (attention or alternative activetreatment); (4) anxiety level data presented both at baseline and afterintervention or training.
Exclusion criteria included the following: (1) qualitative report; (2)literature review; (3) case reports or trials with fewer than 20 subjects;
1There is no single universally agreed upon categorization or defi-nition of meditative therapies. We have decided to use the academicdefinition of meditative therapy in Chinese college textbook to pro-vide a more general focus on integrating breathing, mind, and bodyadjustments into one, which allows us to consider a broad range ofmeditation literature from which to draw a more comprehensive pic-ture in the field. Moreover, the approach including various meditationsis consistent with the existing review in this (see Ospina et al.[6]).
Depression and Anxiety
548 Chen et al.
(4) combined measure of anxiety and stress, or anxiety and depression(i.e. no psychometric measure for anxiety by itself); (5) children oradolescent population.
DATA CODINGOf those papers that qualified for the review after the initial screen-
ing, the full articles were obtained and assessed for their relevancebased on the preplanned criteria for inclusion. Data were indepen-dently extracted by two reviewers using predesigned data collectionform. Any disagreements were discussed with a third reviewer for finaldata coding.
Study quality was assessed using the modified Boutron et al.checklist[41] to evaluate a report of a nonpharmaceutical trial (CLEAR-NPT), which includes a checklist of 10 specific quality assessment crite-ria. This was developed using the Delphi technique with experiencedresearchers assessing report quality of NPT. We chose this check-list instead of the traditional Jadad Scale[42] because it offers morecomprehensive quality details than Jadad (10 assessment criteria in-stead of 5) and offers an alternative when blinding is not possible forparticipants or clinicians in the trial. We added one criterion to theCLEAR-NPT—“were the treatment and control groups comparableat entry?” (see Table A1 for a complete list). Because some criteria maynot apply to the specific study (e.g. when no providers were presentfor some meditation study with waiting-list control), all studies couldnot be evaluated equally on the 11-point scale. Therefore, we applieda quality index (range 0.0–1.0) dividing number of met criteria by totalnumber of applied criteria. In the context of this metric, a score lessthan 0.6 was considered low quality, a score between 0.6 and 0.8 wasconsidered acceptable, and a score greater than 0.80 was consideredgood quality.
Most studies did not provide the full information needed for thequality assessment (e.g. detailed randomization procedure, allocationconcealment, care providers’ experience for each arm, or necessaryquantitative data like means and standard deviations [SDs]). As a result,we attempted to contact the authors to obtain additional informationwhen necessary to provide a more objective assessment of study qual-ity. After three unsuccessful contact attempts, or if the author couldno longer access the pertinent data, we considered this information“unclear” and ranked it as “no” for the quality assessments of thesestudies.
DATA ANALYSISQuantitative data that could be aggregated were entered into the
Cochrane Collaborative Review Manager Software (RevMan v. 5.1)[43]
and analyzed by RevMan analysis, one of the most popular and most au-thoritative literature review softwares. Since the entire outcome mea-sures in the reviewed studies were continuous scales, the standard-ized mean differences (SMD) and their 95% confidence intervals werecalculated using a random effect model built in RevMan 5.1. SMDexpressed the size of the intervention effect in each study relative tothe variability observed in that study. Outcomes were analyzed onthe changes from baseline to the endpoint of the treatment, includingonly the subjects with both a baseline and a final (postintervention)assessment. The outcomes at the later follow-up were not used formeta-analysis unless they reported a larger effect than the endpoint oftreatment. When multiple anxiety outcomes were present in the samestudy, such as state and trait anxiety scales, we chose the change ofSMD in the trait anxiety scale (more stable) rather than state anxiety(less stable) to be included in the meta-analysis. When SD of the meandifference was not available from the paper or from the authors, thebaseline SD (usually larger than that of after-intervention) was used toavoid an overestimation of the SMD.
Figure 1. PRISMA flow-chat of meditation for anxiety review.
Given the fact that the SMD was highly correlated with the type ofcontrol in the study design, we decided to conduct the meta-analysisseparately by three types of control conditions (i.e. waiting list or treat-ment as usual [TAU], attention/education control, and alternative ac-tive therapy) so that we could provide greater details regarding theaccumulated findings and level of evidence in different control con-ditions. We evaluated heterogeneity using the I2 statistic,[43] whichindicates the proportion of variability across trials not explained bychance alone. Roughly, I2 values of 50% or greater represent substan-tial heterogeneity, whereas I2 values of 40% or less is considered noproblem in heterogeneity.[43] We also checked for heterogeneity byvisual examination of forest plots. When substantial heterogeneity wasobserved, we attempted to determine potential reasons for it by re-moving the study with largest effect on overall SMD to examine themagnitude of the effect from that study. When possible, a sensitivityanalysis was performed separately for higher quality studies. Studiesin which means and SDs were not reported and could not be obtainedfrom the authors were not entered into the meta-analysis and werereviewed only narratively.
RESULTSSEARCH RESULTS
The original search identified more than 1,000 ab-stracts from various databases. After careful screening ofthese abstracts, 201 full-text articles were obtained forfurther assessment for eligibility. Of these articles, 155were excluded for reasons described in Fig. 1.
After inclusion and exclusion criteria were applied tothe remaining 46 studies with additional informationfrom the authors as available, six trials were excluded—two studies were based on inappropriate randomizationprocedures[44, 45]; one study had an incompatible anxietymeasure[46]; two studies were not true RCTs,[31, 47] andone study was a comparison between qigong and qigong
Depression and Anxiety
Review: Meditative Therapies for Reducing Anxiety 549
plus the rehabilitation.[48] A summary flow chart with allnumbers of included and excluded studies is presentedin Fig. 1.
CHARACTERISTICS OF INCLUDED STUDIESTable 1 presents the summary characteristics of the
included studies on various meditative therapies used totreat anxiety symptoms. Among the 40 reviewed RCTs,14 studies applied MM or MBSR, 10 used yoga, threetaiji, four qigong, three TM, and six used guided im-agery. Sixteen of the studies (mostly MM) were con-ducted in the United States, six in India, three in otherAsian countries, seven in European countries (Sweden,UK, and Spain), two in Brazil, one in Israel, two inCanada, and two in Australia. A majority of the stud-ies (29) were conducted among patients who had healthproblems other than anxiety disorders but included anx-iety symptoms as one of the outcome measures. Eightstudies were conducted among healthy subjects, andfour studies were conducted among patients with anxi-ety disorders or had anxiety as the primary outcome. Themost frequently used anxiety measures were the Spiel-berg State-Trait Anxiety Inventory (STAI),[49] whichwas used in 20 studies, and the Hospital Anxiety andDepression Scale (HADS),[50] which was used in sevenstudies.
The sample sizes ranged from 20 to 298 (effective casesin data analysis ranged from 18 to 207). Thirty-six studieshad sufficient data to be included in the meta-analysis forquantitative comparison. The pooled sample was com-posed of 2,466 effective unique subjects in the meta-analysis, where 1,151 were in the meditation groups,whereas 1,315 were in control/comparison groups (sixstudies included more than one control group). RCTswith meditative therapies were then be divided into threecategories in terms of the type of control conditions usedfor comparison: waiting-list or TAU control, attentioncontrol (education or nondirective therapies), and alter-native active treatment (such as music therapy, pharma-cotherapy, or other exercises).
The general quality of these RCTs were acceptable asper CLEAR-NPT[41]: sixteen (40%) studies had a qual-ity score of 0.8 or better, indicating a good quality in re-search design; 17 studies (42.5%) fell into the category ofmoderate or acceptable quality (0.6–0.8), and only sevenstudies (17.5%) had a quality score lower than 0.6.
MAIN OUTCOME MEASURESMeta-analyses with SMD for various meditative ther-
apies were conducted by three types of control used forcomparison. Most of the RCTs (28 in total) investigatedthe efficacy of meditative therapies for reducing anxi-ety symptoms by comparing the meditation plus TAUwith the TAU only (for clinical samples of patients, orwaiting-list control for healthy subjects).[13, 28,51–76] Allstudies in this category reported greater reduction ofanxiety symptoms in the meditative group than that inthe waiting list or TAU group, although not all were
statistically significant (see Fig. 2). Eighteen of the 25studies in meta-analysis (72%) reported statistically sig-nificant differences in reducing anxiety between medi-tation group and the control; 12 studies (48%) showedsignificant differences in SMD in comparison with theTAU or waiting-list control (which may be related tothe fact that we used the baseline SD in calculation ofSMD when SD of change was not available). Poolingthe results, we found a statistically significant SMD of–0.52 (p < .001; 95% CI: –0.62, –0.41) based on 1,608unique observations (788 in meditative groups and 820in control group).
Eight RCTs evaluated the efficacy of meditative ther-apies for anxiety in comparison with similar or compa-rable attention.[26,77–83] Two of the studies reported ap-plying supportive counseling in the control group,[81, 82]
but did not give any details on how the counseling wasdelivered, so we treated them as attention control. Allstudies in this category reported significantly greater re-duction of anxiety in the meditative group than that incontrol, and four of them (57%) showed statistically sig-nificant SMD in comparison with the attention control.Overall, we observed a statistically significant SMD of–0.59 (p < .001; 95% CI: –0.79, –0.39) based on 466unique subjects (245 in meditation, and 221 in attentioncontrol) (see Fig. 3).
Ten RCTs compared the meditative therapies withother active therapies for a health issue or anxiety intheir research design (six had more than one controlgroup). These other active therapies included physicalexercises,[54, 63,67] pharmaceutical therapy,[60, 84] musictherapy,[72] progressive muscle relaxation,[68, 85] a reha-bilitation program,[39] or a corporate stress managementprogram.[86] Three studies (30%) reported significantlygreater reduction of anxiety in the meditative group thanthat in control. Although most of these studies did notshow statistically significant differences between medi-tative therapy and the active therapy, meditative therapyseemed to do just as well as, or better than, other activetherapies in comparison. Overall, we found a statisti-cally significant SMD of –0.27 (p = .003; 95% CI: –0.46,–0.09) based on 581 unique observations (307 in medita-tive group and 274 in active therapy group) (see Fig. 4).If we removed the study with the largest effect[49] fromthe analysis (treated it as an outlier), the SMD would bereduced to –0.19 (p = .03; 95% CI: –0.36, –0.02), whichwas much less robust but still significant.
By examining the I2 in heterogeneity analysis, wefound that heterogeneity in the reviewed studies with thewaiting-list control, attention control, and active therapycontrol were all at an acceptable level (since I2 is equalto 8, 10, or 15% accordingly, under the 30% guidelinefor possible problem in heterogeneity as per Cochranehandbook[87]).
SUBGROUP ANALYSISWe conducted subgroup analyses to explore the possi-
ble differences in SMD among studies with waiting-list
Depression and Anxiety
550 Chen et al.
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tau
ra
Depression and Anxiety
Review: Meditative Therapies for Reducing Anxiety 551T
AB
LE
1.C
onti
nued
Per
cent
Dur
a-N
o.of
Ret
Mai
nSt
udy
ofT
ype
Typ
eof
Anx
iety
Gro
upor
Hom
e-tio
nSe
s-ra
teC
LE
AR
findi
ngs
onID
Ns
Age
fem
ale
Cou
ntry
med
itatio
nSs
cont
rol
mea
sure
Indi
vidu
alw
ork
(wks
)si
ons
(%)
scor
ean
xiet
y(a
nx)
Not
es
Kab
at-Z
inn
etal
.(1
998)
[56]
3743
54U
SA(U
S)M
BSR
2W
LST
AI
Ind
N13
1362
0.82
The
rew
asno
sign
ifica
ntdi
ffere
nce
b/n
the
min
dful
ness
and
cont
rolg
pson
STA
I.
Pso
rias
is
Kon
dwan
iet
al.
(200
5)[7
9]
3450
56U
SAT
M2
AT
TM
HI
Bot
hY
5219
810.
8T
Mgp
had
ade
crea
sein
anx
over
time
(p=
.02)
and
asi
gm
ore
decr
ease
inan
xas
com
pare
dto
the
cont
rol(
p=
.03)
Hyp
erte
nsio
n
Koz
asa
etal
(200
8)[5
7]22
4391
Bra
zil
Yog
a3
WL
STA
IG
rpY
42
Unc
0.30
aY
oga
grou
psh
owed
mor
esi
gde
crea
sein
anxi
ety
afte
rtr
eatm
ent(
sig
leve
lnot
avai
labl
e)
anxi
ety
diso
rder
s
Len
gach
eret
al.
(200
9)[5
8]
8458
100
USA
MB
SR2
WL
STA
IB
oth
Y6
698
0.91
Min
dful
ness
gpha
dsi
gnifi
cant
lym
ore
decr
ease
dan
xco
mpa
red
toth
eco
ntro
lgp
(sta
tean
xp
=.0
3,tr
aita
nxp
=.0
04).
Bre
astC
ance
r
Leo
n-P
izar
ro(2
007)
[59]
6624
–82
100
Spai
nG
I3
WL
HA
DS
Ind
Y4
370
0.55
aG
Igp
show
eda
sign
ifica
ntm
ore
decr
ease
inan
x(p
=.0
08)a
sco
mpa
red
toco
ntro
l.
Gyn
/bre
ast
brac
hy-
ther
apy
Lie
tal.
(200
2)[6
0]86
320
Chi
naQ
igon
g2
WL
/AA
HA
M-A
Grp
N1.
5D
aily
100
0.7
Qig
ong
(p<
.001
)and
med
icin
e(p
<.0
5)gp
sha
dsi
ggr
eate
rde
crea
sein
anx
asco
mpa
red
toco
ntro
l.Q
igon
ggp
had
mor
ere
duct
ion
than
med
icin
egp
(p<
.001
).
Her
oin
addi
cts
Ljo
tsso
net
al.
(201
0)[8
0]85
3584
Swed
enM
BSR
2A
TT
VSI
Ind
Y10
Dai
ly95
0.71
Min
dful
ness
gpha
da
sign
ifica
ntm
ore
decr
ease
inga
stro
inte
stin
al-r
elat
edan
x(p
<.0
01,E
S=
0.64
)as
com
pare
dto
the
WL
.
IBS
Mal
athi
and
Dam
odar
an(1
999)
[61]
5018
.5U
ncIn
dia
Yog
a1
WL
STA
IG
rpN
1236
100
0.45
aO
nth
eda
yof
the
exam
and
afte
ryo
gase
ssio
n,th
ere
was
am
ore
sig
redu
ctio
nin
anx
inyo
gagp
asco
mpa
red
toco
ntro
lgp
(p<
.001
)
Med
stud
ents
Man
zane
que
etal
.(2
009)
[62]
3918
–21
87Sp
ain
Qig
ong
1W
LST
AI,
BA
IG
rpY
420
850.
73Q
igon
ggp
had
asi
gnifi
cant
mor
ede
crea
sein
anx
afte
r1
mon
th(p
<.0
1)on
STA
Ias
com
pare
dto
cont
rol.
No
chan
geon
Bec
kA
nxIn
vent
ory.
Hea
lthy
Ss
Depression and Anxiety
552 Chen et al.
TA
BL
E1.
Con
tinu
ed
Per
cent
Dur
a-N
o.of
Ret
Mai
nSt
udy
ofT
ype
Typ
eof
Anx
iety
Gro
upor
Hom
e-tio
nSe
s-ra
teC
LE
AR
findi
ngs
onID
Ns
Age
fem
ale
Cou
ntry
med
itatio
nSs
cont
rol
mea
sure
Indi
vidu
alw
ork
(wks
)si
ons
(%)
scor
ean
xiet
y(a
nx)
Not
es
McM
illan
etal
.(2
002)
[63]
130
3422
UK
MB
SR2
WL
and
AA
HA
DS
Bot
hY
45
850.
64N
osi
gnifi
cant
diffe
renc
esof
chan
gew
ere
foun
don
anx
scor
esb/
nth
eM
Mgp
and
the
phys
ical
exer
cise
and
WL
cont
rolg
ps.
TB
I
Mof
fatt
etal
.(2
010)
[64]
6933
100
Can
ada
GI
2W
LST
AI
Ind
N4
887
1.0
No
sign
ifica
ntdi
ffere
nces
inch
ange
b/n
the
GI
and
WL
cont
rolg
psbu
tpts
repo
rted
posi
tivel
yfo
rth
eir
GI
expe
rien
ce.
Pre
gnan
thbp
Nid
ich
etal
.(2
009)
[65]
298
2661
USA
TM
1W
LP
OM
SIn
dY
1213
690.
89T
heT
Mgp
show
edsi
gnifi
cant
mor
eim
prov
emen
tin
anx
at3-
mon
thfo
llow
-up
(p=
.003
)as
com
pare
dto
the
WL
cont
rol.
Col
lege
stud
ents
Nun
eset
al.
(200
7)[6
6]34
5210
0B
razi
lG
I2
WL
BA
Ian
dST
AI
Grp
Y4
2410
00.
73T
heG
Igr
oup
had
sign
ifica
ntm
ore
decr
ease
inst
ate
anx
(p<
.05;
ES
=0.
52)a
ndtr
ait
anx
(p<
.001
;ES
=0.
79)a
sco
mpa
red
toco
ntro
l.
Bre
astc
ance
r
Oke
net
al.
(200
4)[6
7]69
4977
USA
Yog
a2
WL
and
AA
STA
IB
oth
Y24
2483
0.8
No
sign
ifica
ntdi
ffere
nce
inch
ange
b/n
yoga
gpan
dex
erci
seor
WL
cont
rolg
pson
anx
mea
sure
.
Mul
tiple
scle
rosi
s
Rao
etal
.(2
009)
[81]
7030
–70
100
Indi
aY
oga
2A
TT
STA
IIn
dY
2422
540.
73G
reat
erde
crea
sein
anx
(p<
.001
)am
ong
yoga
gpth
anco
ntro
lpos
tsur
gery
,po
stra
diat
ion
(p<
.01)
,and
post
chem
othe
rapy
(p<
.001
).
Bre
astc
ance
r
Schm
idte
tal.
(201
0)[6
8]17
753
100
Ger
man
yM
BSR
2W
Lan
dA
AST
AI
Bot
hY
89
820.
91A
Agp
ssh
owed
mor
ede
crea
sein
anx
asco
mpa
red
toco
ntro
l(p
=.0
04)b
utno
sign
ifica
ntdi
ffere
nce
b/n
MB
SRan
dac
tive
cont
rol.
Fibr
omya
lgia
Shap
iro
(199
8)[6
9]20
0n/
an/
aU
SAM
BSR
1W
LST
AI
Bot
hY
88
970.
73T
hem
indf
ulne
ssgp
show
eda
sign
ifica
ntm
ore
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ease
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thst
ate
anx
(p<
.05)
and
trai
tanx
(p<
.002
)as
com
pare
dto
cont
rol
Med
Stud
ent
Stre
ss
Depression and Anxiety
Review: Meditative Therapies for Reducing Anxiety 553
TA
BL
E1.
Con
tinu
ed
Per
cent
Dur
a-N
o.of
Ret
Mai
nSt
udy
ofT
ype
Typ
eof
Anx
iety
Gro
upor
Hom
e-tio
nSe
s-ra
teC
LE
AR
findi
ngs
onID
Ns
Age
fem
ale
Cou
ntry
med
itatio
nSs
cont
rol
mea
sure
Indi
vidu
alw
ork
(wks
)si
ons
(%)
scor
ean
xiet
y(a
nx)
Not
es
Shep
pard
etal
.(1
997)
[86]
4450
.515
USA
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AI
Bot
hY
1213
730.
64T
heT
Mgp
show
edm
ore
decr
ease
inan
xat
3m
onth
s(p
<.0
5)as
com
pare
dto
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rol
and
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ern
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inue
dat
3ye
ars
follo
w-u
p..
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lthy
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anet
al.
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2)[7
0]56
27–7
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00.
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osi
gnifi
cant
decr
ease
inan
xfo
rG
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asco
mpa
red
toco
ntro
l.
Can
cer
Smith
etal
.(2
007)
[85]
131
4483
Aus
tral
iaY
oga
1A
AST
AI
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N10
1090
0.82
Yog
agp
had
mor
eim
prov
emen
ton
men
tal
heal
th.B
utno
sig
diffe
renc
esb/
ngp
son
the
STA
I
Hea
lthy
Spec
aet
al.
(200
0)[7
1]10
951
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anad
aM
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SB
oth
Y7
783
0.73
MB
SRha
dsi
gm
ore
decr
ease
dan
xiet
yaf
ter
inte
rven
tion
asco
mpa
red
toth
eco
ntro
l(p
<
.001
).
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cer
Stei
net
al.
(201
0)[7
2]56
6630
USA
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3W
Lan
dA
AH
AD
S;P
OM
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dY
241
100
0.67
The
rew
asno
sig
diffe
renc
eb/
ngp
son
anx
mea
sure
sbu
tpa
rtic
ipan
tsre
port
edlik
ing
GI.
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onar
yB
ypas
s
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lund
etal
.(2
009)
[73]
8244
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eden
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ong
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LH
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rpY
1224
820.
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odi
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nce
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xle
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oved
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ifica
ntly
onan
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ertim
e
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nout
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3)[2
8]18
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88
900.
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hem
indf
ulne
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show
eda
sign
ifica
ntm
ore
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ease
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x(p
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1)an
dth
ere
was
noch
ange
inth
eco
ntro
lgp.
Hea
rtD
isea
se
Tan
eja
etal
.(2
004)
[74]
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dia
Yog
a2
WL
STA
IIn
dY
81
950.
55A
t1m
onth
,the
rew
asa
mor
esi
gde
crea
sein
anxi
ety
inyo
gagp
asco
mpa
red
toco
ntro
l(p
<.0
1),b
utno
tso
at2
mon
ths.
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rall
p<
.05.
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ieta
l.(2
003)
[75]
8852
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anT
aich
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IG
rpN
1236
860.
7T
aich
igp
show
eda
sig
mor
ede
crea
sein
anx
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hst
ate
and
trai
tp<
.01)
asco
mpa
red
toco
ntro
l.
Hyp
erte
nsio
n
Vad
iraj
aet
al.
(200
9)[8
2]88
4710
0In
dia
Yog
a2
AT
TH
AD
SIn
dY
618
–24
890.
6B
oth
the
yoga
gpan
dth
esu
ppor
tive
ther
apy
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rolg
pde
crea
sed
inan
xsc
ores
but
ther
ew
asa
sign
ifica
ntdi
ffere
nce
b/n
the
gps
(p<
.001
).
Bre
astc
ance
r
Depression and Anxiety
554 Chen et al.
TA
BL
E1.
Con
tinu
ed
Per
cent
Dur
a-N
o.of
Ret
Mai
nSt
udy
ofT
ype
Typ
eof
Anx
iety
Gro
upor
Hom
e-tio
nSe
s-ra
teC
LE
AR
findi
ngs
onID
Ns
Age
fem
ale
Cou
ntry
med
itatio
nSs
cont
rol
mea
sure
Indi
vidu
alw
ork
(wks
)si
ons
(%)
scor
ean
xiet
y(a
nx)
Not
es
Wan
get
al.
(201
0)[3
9]34
7755
Japa
nT
aich
i2
AA
GH
Q-A
Grp
N12
1285
0.58
aT
aich
igp
show
eda
sign
ifica
ntm
ore
redu
ctio
nin
anx
(p=
.034
)as
com
pare
dto
the
cont
rol.
Stro
ke
Will
iam
set
al.
(200
8)[7
6]68
18–6
547
UK
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IB
oth
Y8
881
0.8
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dful
ness
gpha
dlo
wer
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than
the
cont
rolg
p(p
=.0
14)
for
bipo
lar
pts,
butn
otfo
run
ipol
arpt
s.
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olar
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orde
r
Wu
etal
.(1
999)
[83]
2638
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igon
g2
AT
TC
SAQ
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Y10
685
0.6
Qig
ong
gpha
dgr
eate
ran
xre
duct
ion
than
cont
rolg
pov
ertim
e(p
<.0
1).
Pai
n
Not
e:T
ype
ofsu
bjec
ts(S
s):1
=he
alth
ysu
bjec
ts;2
=pa
tient
sw
ithhe
alth
prob
lem
san
dan
xiet
ysy
mpt
oms;
3=
patie
nts
with
anxi
ety
diso
rder
s;4
=m
ixed
.T
ype
ofco
ntro
l:W
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aitin
glis
tor
trea
tmen
tas
usua
l;A
TT
,att
entio
n/ed
ucat
ion
cont
rol;
AA
,alte
rnat
eac
tive
ther
apy.
Typ
eof
med
itatio
n:M
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indf
ulne
ss;M
BSR
,min
dful
ness
-bas
edst
ress
redu
ctio
n;T
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rans
cend
enta
lmed
itatio
n;G
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ided
imag
ery;
MB
CT
,min
dful
ness
-bas
edco
gniti
veth
erap
y.A
nxie
tym
easu
re:S
TA
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piel
berg
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ate-
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itA
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vent
ory;
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M-A
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ilton
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iety
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;HA
DS,
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pita
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dde
pres
sion
scal
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kA
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vent
ory;
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ener
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fect
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eive
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omau
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rfo
llow
-up
com
mun
icat
ions
.
Depression and Anxiety
Review: Meditative Therapies for Reducing Anxiety 555
Figure 2. Forest plot of comparison: Meditation versus waiting-list control standardized mean differences.
or attention control, given the large number of RCTsthat were included in the review. There were no sig-nificant differences between the waiting-list control andattention control in the majority of the pooled outcomes(see Table 2 for the results of these exploratory subgroupcomparisons in SMD of meditative therapies for reducedanxiety).
Overall, there were no statistically significant differ-ences in the pooled results of SMD among the major-ity of subgroup comparisons with two exceptions: studyquality and region of the study being conducted. There-fore, we cannot draw conclusions solely based on thesecomparisons. The subgroup comparisons suggest thatmoving meditation such as qigong, tai chi, or yoga prac-tice seemed to produce the larger effect in terms of
pooled SMD (–0.68 to –0.63) of reduced anxiety thanthose by the static meditation such as guided imagery(–0.39) or mindfulness (–0.51). The longer meditationduration did not add any additional effect. No differencewas found in terms of density of meditation, or type ofstudy subjects, or homework assignment; however, wedid see a trend in which studies with group delivery re-ported higher SMD (–0.58) than those with individualdelivery (–0.44). Again, most of the subgroup differenceswere not statistically significant. We also noticed that allstudies with healthy subjects (six in total) reported sig-nificant differences in reduced anxiety between the med-itation group and control group.
Two significant subgroup differences were found inthe region where the study was conducted and in the
Figure 3. Forest plot of comparison: Meditation versus attention control standardized mean differences.
Depression and Anxiety
556 Chen et al.
Figure 4. Forest plot of comparison: Meditation versus Alternative active therapy group standardized mean differences.
study quality. Those studies conducted in the easterncountries (India, China, and Japan) had a significantlylarger effect than those conducted in the western coun-tries (–0.77 versus –0.46; p =.04), where meditation maybe considered of less mainstream. As to the differences in
study quality, the lower quality studies tended to reporta larger effect than the high-quality studies. Those stud-ies with a CLEAR-NPT score less than 0.6 reported amean SMD twice as much as those studies with a qualityscore greater than 0.8 (–0.83 versus –0.40; p = .02).
TABLE 2. Exploratory comparisons of subgroup differences in SMD of reduced anxiety among studies with waiting-listcontrol or attention control
Subgroups No. of studies No. of subjects SMD (95% CI) p values (grp differences)
Total 32 2,074 −0.53 (−0.62, −0.44)By type of meditationa
Mindfulness meditation 11 869 −0.51 (−0.64, −0.37) .48Yoga 9 424 −0.63 (−0.88, −0.38Qigong or tai chi 5 288 −0.68 (−1.07, −0.29)Guided imagery 5 252 −0.39 (−0.64, −0.14)
By duration of study4 weeks or shorter 9 453 −0.57 (−0.77, −0.36) .816–10 weeks 12 771 −0.56 (−0.71, −0.42)12 weeks or longer 11 850 −0.50 (−0.66, −0.33)
By density of meditation trainingb
Weekly or less 20 1,379 −0.51 (−0.62, −0.40) .462+ a week to daily 10 612 −0.60 (−0.81, −0.39)
By training/therapy delivery methodGroup or group plus Individual 23 1,402 −0.58 (−0.70, −0.46) .17Individual 9 672 −0.44 (−0.60, −0.29)
By homework assignmentc
With homework 26 1,735 −0.52 (−0.61, −0.42) .83Without homework 5 279 −0.56 (−0.98, −0.15)
By Region of studiesFrom Western countries 24 1,631 −0.46 (−0.56, −0.27) .04From Eastern countries 8 443 −0.77 (−1.04, −0.50)
By quality of the studyCLEAR-NPT ≥ 0.8 12 981 −0.40 (−0.53,−0.27) .02CLEAR-NPT: 0.6—0.8 14 858 −0.61 (−0.75, −0.46)CLEAR-NPT < 0.6 6 235 −0.83 (−0.15, −0.50)
By Type of Subjectsd
Patients with other health issues 22 1,410 −0.53 (−0.65, −0.41) .91Healthy subjects (not patient) 6 489 −0.54 (−0.73, −0.35)Patients with anxiety issue 3 127 −0.61 (−0.97, −0.25)
aTwo studies of TM were not included in subgroup analysis.bTwo studies ran only one session of meditative training and were not included.cOne residential study was not included.dOne study with mixed subjects was not included.
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A close examination of these studies for possible ad-verse effects found no reported side effects and most didnot report the procedure for addressing adverse effects ormention safety examination. Among the studies that ex-amined safety issues in the paper,[39,67, 68] none reportedany adverse effect from meditative therapies.
CONCLUSIONSSUMMARY OF MAIN RESULTS
The current review and meta-analysis of a numberof small-to-medium scale quality RCTs showed someconsistent and robust evidence that meditative therapiesmay be an effective treatment for patients with anxietysymptoms. The pooled effects of meditative therapies foranxiety were clinically relevant when compared with thewaiting-list (or TAU) and the attention controls, but notas robust when compared with other active or alterna-tive therapies. In other words, evidence from this reviewindicates that meditative therapies are more effectivethan waiting-list control or attention control, and maybe considered as effective as other alternative therapiesused in these studies (such as music therapy, exercises,or relaxation practice) for reducing anxiety symptoms.
Differing from the findings in previous reviews ofmeditation, we found that quality of the reviewed RCTswas improved, mostly acceptable, and some of them(40%) were of good quality. This different finding instudy quality may be related to several factors. The firstfactor is the quality criteria used to assess the studies.Specifically, most previous reviews used a standard Jadadscale,[42] which emphasizes significance of blindness. Be-cause blindness is hard to implement in a meditationstudy, we believe this is an overly strict criteria and there-fore we used a more practical quality checklist (11 crite-ria instead of 5) that was designed for nonpharmaceuticaltrials. The second factor is the procedure of review. Wetried to contact most authors for clarifications in detailedresearch design, treatment outcomes, and other qual-ity issues while most previous reviews, including Ospinaet al.[6], did not appear to apply this critical procedure.The third factor is the overall quality of meditation stud-ies have increased continuously in the past 10 years. Ouranalysis of study quality over time indicates that stud-ies published prior to 2000 had a relatively lower qual-ity score (CLEAR = 0.66), studies published in 2000–2005 had slightly higher quality score (CLEAR = 0.69),whereas studies published after 2006 had a mean qualityscore of 0.75. Obviously, our new review included morerecently published high-quality studies, which likely in-dicate better data quality but also better control condi-tions and checks to limit specious findings.
Our analysis revealed that quality of the RCT di-rectly affects the magnitude of the observed effect size.Although somewhat speculative, this implies that the re-sults of low-quality studies may reflect a greater exper-imenter effect or other research biases. This is partic-ularly problematic, because study quality is extremely
important when evaluating the efficacy of a specifictherapy. We also found that the studies conductedin Eastern countries (India, China, and Japan) had asignificantly larger effect than those conducted in theWestern countries (–0.77 versus –0.46; p = .04). Thisfinding may reflect a few factors, including the follow-ing: (1) differing degrees of acceptance of meditationas part of mainstream interventions (Eastern countrieshave higher acceptance than Western countries); (2) thequality of study design (researchers in Western countriesmay apply higher standard or quality control proceduresthan those in Eastern countries, or there may be moreroom for experimenter bias in the Eastern studies whereexperimenters may believe more strongly in the benefitsof these approaches); and (3) differing degrees of expe-rience with meditation (researchers in Eastern countriesmay be more experienced with meditation).
LIMITATIONS AND CHALLENGESAlthough the findings of this review suggest some
promising clinical benefits of meditative therapies foranxiety, we also must acknowledge some limitations thatreduce our ability to draw conclusions from these re-sults. First and foremost, the diversity of meditationmodalities and study designs make it difficult to drawa general conclusion based on the evidence, particularlybecause the effects of meditative therapies on anxiety dif-fer depending on whether the meditation is comparedwith a waiting list (or TAU), additional attention con-trol, or alternative active therapies, and depending onthe quality of studies. The clinically relevant effects ofmeditative therapies for anxiety when compared with awaiting-list or usual care control, or with the attentioncontrol, may be partially attributable to possible placeboeffects of meditative settings (for example, relaxing mu-sic in most meditation settings, or belief that meditationworks before signing up for the study). It is a method-ological challenge to design a compatible control whenthe intervention or treatment involves the patient’s ac-tive participation, making it impossible to blind the par-ticipants to which group they were assigned to, and tohave a meaningful control group that will take the sameamount of time and effort in treatment without substan-tial benefits to the studied health condition. The tradi-tional double-blind placebo-controlled design used forpharmaceutical clinical trials is not applicable to this kindof therapy,[88] as in RCTs evaluating psychotherapy.[89]
However, different from research design in psychother-apy, meditation studies involved more elements of ac-tive participation and daily practice from the study sub-jects, and thus it may be even more difficult to applythe standardization procedure for quality control andfor therapy compliance. Therefore, results in this typeof RCT may be more influenced by potential placebo ef-fects and suggest the need to identify more innovative re-search designs and comparable control conditions to en-able true evaluation of effectiveness in reducing anxietyoutcomes.
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Figure 5. Funnel plot of studies comparing meditation groupwith waiting-list control.
Participants’ preferences and expectations may alsopartially explain the findings. For example, we foundmore patients discontinued study participation in bothwaiting-list and attention control groups than those inactive meditation groups in many of the reviewed studies(although this difference was not statistically significant).It also was evident that the pooled effect size or SMD incomparison with attention control (–0.59) was actuallyslightly higher than those in comparison with waiting-list or TAU control (–0.52), suggesting that participantsdid worse in an attention control compared to a usualcare or waiting-list control (two of seven studies using anattention control group actually reported increased anx-iety following the control condition). This may reflectparticipants in an attention control group being moreaware of their assignment to a control. It is difficult toascertain how observed benefits are attributable to spe-cific effects of meditation.
Another potential limitation of the studies reviewedis the relatively small sample size in most studies, espe-cially those studies using other active therapies as thecomparison conditions. Most reviewed studies includedfewer than 100 participants (average n = 80). Addition-ally, there was a wide range of study duration, with med-itation training ranging from 1 day to 1 year. Althougha funnel plot of all studies in waiting-list control indi-cates a relatively symmetric pattern, suggesting no ob-vious publication bias in the literature itself (see Fig. 5),most studies with nonsignificant SMD were with smallersamples (larger standard error in y-axis). This limitationmakes it hard to draw any firm conclusions regardingeffectiveness. Future larger scale studies are needed tocontinue to assess the efficacy and effectiveness of med-itative therapies.
Finally, several issues must be considered in terms ofthe clinical implications of the observed effects. First, thelarge majority of the reviewed studies measured the re-ductions in nonclinical levels of anxiety symptoms, andfew studies have assessed the clinical efficacy of medita-tive interventions for diagnosed anxiety disorders, which
is what most clinicians are confronted with in clinical set-tings. Therefore, conclusions about the impact of med-itational approaches must be tempered as they relate toclinically relevant manifestations of anxiety. Addition-ally, existing literature has not reported on the effect ofmeditation quality or compliance on the treatment out-come, although it is assumed that quality of meditationwill affect the effect size or overall conclusion. Similarto the need for monitoring drug-intake during phar-maceutical trials, studies of meditative therapies shouldtake into account the quality of meditation and propor-tion of participants who are able to comply with pro-tocol to truly assess the therapy’s feasibility and effec-tiveness. Among the reviewed studies, 20 of 40 studies(50%) examined the quality or compliance of meditationpractice as part of research design; however, few actu-ally compared the differences in outcomes between thelow-compliance group and the high-compliance group.Future studies of meditation should more carefully ad-dress this issue.
IMPLICATIONS AND FUTURE DIRECTIONSThis review indicates the potential effectiveness of
meditative therapies in reducing anxiety. However, afew key considerations must guide future work. Med-itative therapy is not a stand-alone therapy in thetraditional clinical setting, and may not be able to be ad-equately studied using traditional double-blind placebo-controlled trial methodology. Therefore, it may not beappropriate to apply all traditional clinical criteria to as-sess the safety and efficacy issues in meditative thera-pies. Meditation is a whole package of mind–body exer-cise with possibility of change in life style or attitude,which includes both specific and nonspecific effects.These reviewed studies suggest that people with anxietysymptoms may find meaningful benefits through med-itation or related exercise, although it cannot be deter-mined whether these benefits may be mediated throughplacebo, expectation, or self-suggestion.
Second, application of the modified quality assessmenttool in our review suggests that most studies of medi-tative therapies for anxiety are actually of good or ac-ceptable quality, and the results of these studies can betaken into consideration in future work. As quality of thestudies may directly affect the reliability of the results,it is relevant that many high-quality studies in this re-view reported significant differences in reducing anxietybetween the meditation and control groups. This is a dis-tinct difference between this review and what previousreviews have concluded.
In conclusion, our systematic review and meta-analysis suggests that meditative therapy may be an effec-tive option for reducing anxiety symptoms. Our findingssuggest that meditation works significantly better thanTAU or attention control and works as well as otheractive therapies used in these studies for reducing anx-iety. However, to date, clinical efficacy of meditativeintervention for anxiety disorders has not been well
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documented. Although more large-scale studies with im-proved quality are needed to develop more specific clin-ical guidelines for its applications and firm conclusionsregarding its efficacy, the current review does suggestmeditation to be a potential intervention for anxiety.Highlighting the effects of meditation on anxiety is im-portant in that it may provide a useful alternative to exist-ing pharmacotherapy and psychotherapy approaches totreat anxiety. Given the fact that meditative therapies areso easy to carry out without any known adverse effect, andthe fact that no existing treatment is effective for all pa-tients or for all anxiety disorders, clinicians may considerrecommending meditation for patients of anxiety andpromoting meditative therapies for anxiety and relateddisorders.
Acknowledgments. This study was partially sup-ported by an independent investigator award from Brain& Behavior Research Foundation (a.k.a. NARSAD) toDr. Kevin Chen, and a research grant (R24 AT001293)from the National Center for Complementary and Al-ternative Medicine (NCCAM) at the U.S. NationalInstitutes of Health, to the Center for IntegrativeMedicine at University of Maryland Baltimore (PI:Dr. Brian Berman). This paper’s contents are solelythe responsibility of the authors and do not nec-essarily represent the official views of NARSAD orNCCAM.
APPENDIX
TABLE A1. Meditation for anxiety review—qualityassessment
Criterion Yes No Unclear
1 Was the generation of allocationsequences (group assignmentprocedure) adequate?
2 Was the treatment allocationconcealed?
3 Were details of the interventionadministered to each groupstated or made available?
4 Were care providers experience orskill in each arm (group)appropriate?
5 Was participant adherence orcompliance assessedquantitatively?
6 Were participants adequatelyblinded?
� If NO, please go to 6.1.1 and6.1.2.
� If YES, please go to 76.1.1 Were other treatments and care
(i.e. co-interventions) the samein each randomized group?
TABLE A1. Continued
Criterion Yes No Unclear
6.1.2 Were withdrawals andlost-to-follow-up the same ineach randomized group?
7 Were care providers for theparticipants adequately blinded?
- If NO, please go to 7.1.1 and7.1.2.
- If YES, please go to 8.7.1.1 Were all other treatments and care
(co-interventions) the same ineach randomized group?
7.1.2 Were withdrawals andlost-to-follow-up the same ineach randomized group?
8 Were outcome assessorsadequately blinded to assess theprimary outcomes?
8.1 If outcome assessors were notadequately blinded, were specificmethods used to avoidascertainment bias (systematicdifferences in outcomeassessment)?
9 Was the follow-up schedule thesame in each group? (paralleldesign)
10 Were the treatment and controlgroup comparable at entry (anysignificant differences atbaseline)?
11 Were the main outcomes analyzedaccording to theintention-to-treat principle?
Total Total scores (number of Yes)
[Adapted from Boutron et al. (2005)[41]
Checklist to evaluate a report of a nonpharmacological trial(CLEAR NPT)
Quality score = total number of yes/total number of applied criteria.
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