Anxiety disorders are among the most prevalent mental health problems found in the community in the United Kingdom according to the survey carried out by the Office for National Statistics (ONS) in the year 2000.¹ Conditions such as mixed anxiety and depressive disorder, generalised anxiety disorder, phobias, obsessive compulsive disorder, and panic disorder make up over 86% of neurotic disorders found. Excessive anxiety is a key component or symptom in all of these conditions.

Yoga is defined as a practice consisting of three components: gentle stretching; exercises for breath control; and meditation as a mind-body intervention.² The version used mainly in the West is hatha yoga, which consists of an integration of asana (postures), pranayama (breathing exercise), and meditation.³ Although yoga has its origins in Indian culture and religion, it can be practised secularly.² No systematic reviews have been published on the benefits of yoga in anxiety or anxiety disorders. This is despite the fact that a recent analysis of publication trends has shown an increase in publication frequency and growing use of randomised controlled trials to study yoga as a therapeutic intervention.⁴ The only systematic review that looks specifically at yoga as an intervention for any condition is that on yoga in epilepsy, which was inconclusive because of a lack of studies.⁵

The effect of exercise on anxiety has, however, been reviewed. There is some evidence of an anxiolytic effect,⁶ with aerobic exercise possibly more beneficial than non-aerobic exercise.^7,8 There is also some evidence that exercise may be particularly beneficial in people with more severe anxiety.^7,9 None of these reviews, however, appear to have included yoga as a form of exercise.

There are a number of studies that look at the effects of yoga on anxiety levels in non-clinical samples. Berger and Owen¹⁰ compared the effects of swimming, fencing, body conditioning, and yoga classes and found that only the yoga treatment group recorded a significant short term reduction in state anxiety. Ray et al¹¹ reported that yoga reduced anxiety but only among male students. Netz and Lidor¹² showed that participants in yoga as well as swimming and the Feldenkrais method recorded lower anxiety levels than a control group. However, in a study of elderly people, Blumenthal et al^13,14 found that yoga participants fared worse than those in an aerobic exercise group and no better than the other treatment regimens on anxiety measures. It is difficult to predict on the basis of the findings of these studies the effect of yoga on people with anxiety or a specific anxiety disorder, and therefore it is important to identify the evidence that is currently available.

METHODS

Aim and objectives

The aim of this study was to evaluate the evidence from a range of sources of the effectiveness of yoga for the treatment of anxiety and anxiety disorders.

Summary of the search strategy

A comprehensive search for clinical research was carried out. Searches were conducted on major biomedical and specialist databases and websites. Citations were sought from relevant reviews and various appropriate specialised books. Relevant websites were also included in the search, including those of specialist yoga and mental health organisations.

Databases

The following databases were searched between March and June 2004:

• General databases: ClNAHL, Cochrane Central Register of Controlled Trials (CENTRAL), Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects, EMBASE, Medline (and PubMed), PsycINFO

• Specialist CAM databases: AMED, CISCOM

• Specialist yoga websites: International Association of Yoga Therapists,¹⁵ Yoga Biomedical Trust¹⁶

• Specialist mental health websites: MIND,¹⁷ Mental Health Foundation¹⁸

A search of the Cochrane Collaboration Depression, Anxiety and Neurosis (CCDAN) Controlled Trials Register was also conducted in December 2004.

Search terms

The following terms for yoga and anxiety were used in the search of AMED, CINAHL, EMBASE, Medline and PsycINFO (OVID): (exp yoga OR yoga.mp OR yogic.mp OR asanas.mp OR dhyana.mp OR pranayama.mp OR meditation OR meditat*) AND (exp anxiety OR exp anxiety disorders OR anx$.mp).

Search strategies were adapted for each of the databases searched. The searches of CISCOM and CCDAN were carried out by the information specialists responsible for these databases. Efforts were made to identify unpublished and ongoing research using relevant databases such as the National Research Register (UK) and Clinicaltrials.gov (US).

Filtering

This was carried out by two independent researchers, and relevant research was categorised by study type according to a flow chart system developed for this project.

The basic categories used were: randomised controlled trials; controlled clinical trials without randomisation; uncontrolled clinical trials and case series; case reports/studies; qualitative research; surveys; other research studies.

Selection criteria

Types of study

All clinical trials, controlled and uncontrolled, were identified, but only controlled trials, whether randomised or not, were included in this review. Dissertation abstracts were excluded because of lack of detail of methodology and outcome measures. Attempts were also made to locate relevant qualitative studies.

No language restrictions were imposed at the search and filtering stage.

Types of participants

All studies were included in which participants were described as suffering from anxiety. This primarily took the form of a diagnosis of an anxiety disorder by whatever diagnostic method was deemed appropriate by the papers’ authors. In addition, studies in which participants were suffering from anxiety as determined by the authors via measurement scales and those in which participants were about to undergo a procedure that was anticipated to be anxiety provoking were also included.

Types of intervention

Yoga of various styles. Studies where the intervention was solely meditation based were not included.

Types of outcome measures

Anxiety rating scales and scales to measure specific symptoms of anxiety disorders.

Data collection and appraisal

Data was extracted systematically using a specially designed data extraction form. Data extracted included details of selection criteria and procedure, the participants, the intervention and any comparison or control intervention, aspects of the methodology, and outcome measures and results.

Clinical trials were appraised using a standardised appraisal framework specifically developed for this project and based on criteria recommended by the Centre for Reviews and Dissemination.¹⁹

Study quality was measured by recording details of method of randomisation, concealment of allocation, blinding of assessors, and loss to follow up. Also recorded were statistical power, presence or absence of intention to treat analysis, reporting of baseline characteristics, and outcome measures reported.

For each study, two researchers conducted data extraction and appraisal independently, and any disagreements or discrepancies were resolved by discussion. Where consensus could not be obtained, a third reviewer was available for consultation.

Data analysis

The primary outcome measure was taken to be that stated by the study or the first anxiety measure mentioned if none was identified. Additional post hoc (calculated as part of this review) calculations, including the mean difference and standardised mean difference (effect size), were performed where possible to estimate the effect and to allow comparisons to be made between the studies.²⁰

Clinical commentaries

A clinician with relevant training and experience was asked to comment on each study focusing on clinical relevance and practical issues. Commentary frameworks were specifically developed for this project, and these incorporate a number of closed and open questions with space for further comments. Table 1 provides summaries of these commentaries.

RESULTS

Systematic reviews

There were no systematic reviews found specifically on the topic of yoga for anxiety or anxiety disorders, although yoga is included in a systematic review of complementary and self help treatment for anxiety disorders.²¹

Randomised and non-randomised controlled trials

Eight studies were found. All were controlled trials; six were randomised^22–27 and two were non-randomised.^28,29 In five studies the inclusion criterion was a diagnosis of an anxiety disorder (anxiety neurosis, obsessive compulsive disorder, and psychoneurosis).^{22–24,28,29} In two studies participants were suffering from anxiety, namely examination anxiety and snake phobia, as determined by the authors from measurement scales,^25,27 and in the remaining study, participants were about to undergo a procedure, which was anticipated to be anxiety provoking, namely an examination.²⁶

Other studies

No relevant qualitative research studies were located.

Excluded studies

Four studies (five papers) were excluded in which the participants were ostensibly healthy, and anxiety was measured as one of a battery of outcome measures.^10–14 A brief description of these has already been given in the introduction. Four studies in which the primary inclusion criterion was a physical illness were excluded.^30–33 Two studies were excluded because of the lack of a control group.^34,35

Language of studies included

All studies were in English, six were from India and one each from the United States and Canada.

Summary of each study

Table 1 presents a breakdown of the study methodology plus the main results as identified in the original study plus post hoc calculations.

In a hospital based study in the United States, Shannahoff-Khalsa et al²² used yoga as a treatment intervention for obsessive compulsive disorder (OCD). Study participants were all from the community, each with a confirmed DSM-III-R (Diagnostic and statistical manual of mental disorders, third edition, revised) diagnosis of OCD. The sample was randomised, with 12 practising a version of kundalini yoga, which consisted of a number of techniques including mantra meditation as well as an OCD specific technique, which involved breathing through only the left nostril (see Shannahoff-Khalsa et al³⁶ for full details). The remaining 10 patients practised a control regimen, which was also meditative, enabling the researchers to test the hypothesis that “meditation techniques in general may not be effective” and that “disorder-specific” techniques may be required. At three months, the yoga group showed significantly greater improvements on the Yale-Brown obsessive compulsive scale and other scales than the control group. Post hoc analysis indicates, however, that this may only be true under the assumption of equal variances (table 1). A reduction of 20–35% on the Yale-Brown obsessive compulsive scale is deemed clinically significant by the authors. This was achieved for the yoga group (38.4% reduction) but not the control group (13.9% reduction).

Two hospital based Indian studies investigated yoga as a treatment for anxiety neurosis among psychiatric outpatients diagnosed by either Feighner’s diagnostic criteria²⁸ or DSM-III.²³ In a non-randomised study, Sharma et al²⁸ found significantly greater improvement in the yoga group than the placebo control group on the Hamilton anxiety scale measures, at least in the first three weeks of the trial. After three weeks there was a reduction of 23.7% among the yoga group. This reduction is likely to be of clinical significance; however, the mean Hamilton anxiety scale score of 22.7 after the intervention is still at a level that would normally require treatment.³⁷ Other results based on the subjective intensity of anxiety symptoms were more mixed. Sahasi et al²³ compared yoga with diazepam, an established anxiolytic, in a randomised controlled trial. At the end of the three month trial, the authors discovered that the yoga group had recorded significantly lower Institute for Personality and Ability Testing anxiety scale scores and symptom sign inventory scores, findings that were not replicated in the diazepam group. They also found that overall improvement as assessed by the consultant psychiatrist was greater for the yoga group (76.7%) than for the diazepam group (50%), although no statistical significance is attached to this. A post hoc t test on the between group mean difference for the Institute for Personality and Ability Testing score was non-significant (table 1).

Vahia et al^24,29 conducted two studies as part of a larger nine year trial of what they term psychophysiological treatment for psychoneurosis. Psychoneurosis is a term no longer used as a diagnosis, which originally referred to both anxiety and depressive disorders. The psychophysiological treatment was a form of yoga based on the concepts of Patanjali. In the first of the studies,²⁴ the yoga treatment was compared with a pseudo-yoga treatment, designed to act as a control which could ensure patient blinding. Both groups of participants were equivalent for baseline anxiety measured by Taylor’s anxiety scale. After their respective treatments, the genuine yoga group recorded significantly lower anxiety scores than the control group. In the second study,²⁹ yoga treatment was compared with the anxiolytic and antidepressant drugs chlordiazepoxide and amitriptyline, this time among patients with a diagnosis of either psychoneurosis or psychosomatic disorder. The results suggested that the patients who had practised yoga recorded a significantly greater reduction in Taylor’s anxiety scale score than those in the drug group.

Two Indian studies investigated the use of yoga as a treatment for examination anxiety.^25,26 Broota and Sanghvi²⁵ carried out a three way comparison between their Broota relaxation technique, Jacobson’s progressive relaxation technique, and a control among university students who had a history of examination anxiety and recorded a high baseline score on Spielberger’s test anxiety scale. The Broota relaxation technique consists of a set of four exercises adapted from yoga, combined with auto-suggestion. After the three day intervention, the Broota relaxation group recorded a significantly greater improvement on the anxiety check list measure than the Jacobson’s progressive relaxation group and the control group. There were no significant between group differences for the self evaluation ladder scale measure. In a three month trial conducted with medical students, Malathi and Damodaran²⁶ found a significant reduction in anxiety after treatment for the yoga group one month before examinations and on the actual day of examinations. There was no such significant reduction for the control group. Post hoc t tests between the group means after treatment showed a significant difference one month before the examination and on the day of the examination (p<0.001 for both). No such difference existed before treatment at either time point. On the day of the examination, the mean state-trait anxiety inventory score for the yoga group fell by 34.0% from the moderate anxiety range before treatment to the low anxiety range after treatment, representing a clinically significant change.³⁸

Finally, in a study of the management of specific phobias, Norton and Johnson²⁷ treated snake anxious, first year psychology students with either yoga or progressive relaxation. The aim of the study was to test the hypothesis that yoga may be more appropriate for cognitive anxiety whereas progressive relaxation may be more beneficial for somatic anxiety. The results give some support for this hypothesis.

Out of the eight studies described above, standardised mean differences were calculated for only three studies where there were sufficient data and are presented in table 1.

Appraisal of the methodology

Measure of study quality

The reporting of study methodology was poor in most of the studies, and there were also some methodological inadequacies (table 1). The potential for bias is therefore high. Although six out of eight studies were randomised, only one showed an adequate method of randomisation and allocation concealment.²² One study used an inadequate serial numbering method with a subsequent block move of patients to the control group because of an inability to perform yoga.²³ In all the other randomised controlled trials, no detail of the method of randomisation or concealment of allocation is given. Given the nature of yoga, blinding of participants would generally not be considered feasible. Two studies were described as double blind,^24,29 although participants were not blinded in one of the studies.²⁹ It is still possible to blind the outcome assessor, and this was carried out in both of these studies,^24,29 but was either not done, was not possible because of self assessment, or is not mentioned in the others. There was a large loss to follow up in the studies by Sahasi et al²³ and Sharma et al²⁸ (beyond three weeks), and this was a concern in the paper of Shannahoff-Khalsa et al,²² which may bias the results. None of these three studies gave any reasons for the dropouts, and no detail at all was given in the others.

Other methodology

Only one study reported a power calculation, fulfilled the minimum sample size even allowing for dropouts, and gave information on the clinical significance of the results.²² The issue of clinical significance has been addressed in this review where possible, but two of the studies lacked sufficient data,^23,29 two studies used their own scales,^25,27 and the necessary information on the scale used in one was not available.²⁴ In only one of the studies was any intention to treat analysis carried out and reported.²² Two of the studies clearly did not calculate their results on this basis,^23,28 and in the others there was no mention of this issue or there was insufficient detail to deduce the basis of the calculations. The reporting of age, sex, and baseline anxiety distribution between the groups was inadequate in some studies.^23–29 This is a particularly serious problem in the study by Sahasi et al²³ because of the block move of participants after randomisation. Three studies detailed age and sex distribution.^22,23,28 Baseline anxiety figures for the primary outcome measure were satisfactorily equivalent between the treatment groups in three studies,^22,24,26 and in one study equivalence is stated.²⁷ The main co-interventions dealt with were concurrent drug treatments and psychotherapy. Three of the studies gave some detail on this issue, but none of them dealt with it in any way adequately or checked that any instructions given were adhered to.^22,23,28 The other studies gave no detail on this issue. Feighner’s diagnostic criteria, a forerunner to the inclusion of diagnostic criteria in the DSM, was used in one study.²⁸ Two studies did not state which diagnostic criteria they used.^24,29 Two of the studies had errors in the labelling in the tables, which necessitated some assumptions in the interpretation of the data in them.^26,27 In one study, some of the data reproduced in the tables were unreliable.²⁸

Statistical methods

Adequate statistical methods were used in most studies.^{22,25,27–29} In one study where only a pre-post t test for each group was performed, there were sufficient data to allow a post hoc, between group comparison on the mean difference to be performed.²³ The remaining two studies had only sufficient data to allow a t test on the post-test means, although baseline equivalence with respect to anxiety measure ensured that this comparison was meaningful.^24,26

DISCUSSION

A number of controlled trials, both randomised and non-randomised, that tested yoga as an intervention with respect to anxiety and anxiety disorders are described in this review. There were eight studies in which participants were suffering from anxiety or had a diagnosed anxiety disorder, and all registered positive results in favour of yoga. However, the overall reporting of study methodology was poor, and there were many methodological inadequacies in the studies. It is encouraging though that the best study methodologically²² provided a positive result.

The smallest standardised mean difference was in the study by Sahasi et al,²³ which is perhaps not surprising given the choice of diazepam as a control treatment. The other two studies that had sufficient data to allow standardised mean differences to be calculated produced respectable figures demonstrating a notable effect.^22,28

There is a shortage of information on safety or contraindications with respect to yoga for psychiatric disorders. Little additional information on adverse effects related to the practice of yoga can be gained from the studies included in this review. Shannahoff-Khalsa et al²² reported an absence of adverse effects, but there is no mention of adverse effects within the other studies. As well as recommending that medical advice be sought before yoga is taken up by anybody with a medical condition, Ernst² states that certain postures are not recommended during pregnancy, that overstretching joints may lead to physical damage, and that the meditation aspect may best be avoided by anyone with a history of psychotic or personality disorder. Becker⁴¹ states that meditation is impossible in the presence of active psychosis. No further details or references are given in either source. The evidence in general on contraindications with regard to psychosis and possible psychotic side effects of meditation appears at this stage to be in the form of case reports,^42,43 and is certainly an area that requires more investigation. With exercise in general, there is some concern that undertaking a programme that is too intense for a person can lead to a worsening of mood.⁷

Motivation and compliance may also be issues that require consideration before recommendation of a programme such as yoga.⁴¹ Low participation and high attrition rates, 50% lost within three to six months, have been found for exercise.⁷ Dropout rates were significant or high in all three studies that reported on this.^22,23,28 The ability to pursue a commitment to a yoga programme may well be an issue for clients with anxiety disorders, as may the type of yoga used. There are many different forms of yoga,⁴⁴ and some may be more suitable than others. Careful consideration should be given to these matters before recommendation of any programme, and it would be desirable for instructors to have suitable mental health experience. Nespoor⁴⁵ provides some useful tips on compliance, such as using family support structures and emphasising the non-competitive nature of yoga.

The issue of publication bias has not been dealt with, although efforts were made to find unpublished studies and ongoing research. It is possible, however, that other, less positive findings remain unreported. A meta-analysis of the results was not considered appropriate because of insufficient data and study heterogeneity, mainly in the conditions treated.

If yoga does produce an anxiolytic effect, the exact causal mechanism is likely to be complex. Yoga may best be delivered as a complete intervention, and if different aspects are delivered separately, such a reductionist approach may result in loss of efficacy or effectiveness. Having said that, it is still worth while devising appropriate controls in an attempt to tease out the yoga specific effects. Similar to exercise, biochemical or physiological mechanisms as well as improvements in self esteem and social situation may well be important,⁴⁶ as could distraction from negative thoughts.⁷

Yoga is an attractive therapeutic option because of its popularity recently demonstrated in the United States,⁴⁷ and, like exercise, may be of particular use where clients reject ostensibly psychological diagnoses and treatments.⁷ The National Institute for Clinical Excellence (NICE) recommend that patients with panic disorder and generalised anxiety disorder are informed about exercise as part of good general health.⁴⁸ If proved efficacious, yoga would be an attractive option because it is non-pharmacological, has minimal adverse effects if practised as recommended, and enjoys international acceptance.⁵

In summary, the eight studies reviewed here report positive findings for the use of yoga in OCD,²² examination anxiety,^25,26 snake phobia,²⁷ anxiety neurosis,^23,28 and psychoneurosis,^24,29 although the latter two diagnostic terms are no longer used. There were, however, many methodological inadequacies, and only the OCD study²² could be described as being methodologically rigorous.

Owing to the diversity of conditions treated and the poor quality of most of the studies, it is not possible to say that yoga is effective in treating anxiety or anxiety disorders in general. However, there are encouraging results, particularly with OCD. Further well conducted research is necessary which may be most productive if focused on specific anxiety disorders.