Yoga is a practice originating in India which usually consists of physical exercises (stretches orasanas), breathing techniques and meditation or relaxation. It is taught in yoga classes or on a one-to-one basis, can be practised by the individual or is incorporated into stress management programmes.
Yoga is claimed to have a range of physical, psychological and spiritual benefits.
Fourteen systematic reviews focus on yoga in breast cancer or include mainly trials in breast cancer. These address a wide range of outcomes. The quality of the included trials varied considerably and only very low quality evidence is available to show that yoga may be comparable to other exercise-based interventions. Quality is mainly affects by the risk of bias due to blinding not being feasible and subjective outcomes being self-assessed.
- Quality of life/well-being: The reviews demonstrate evidence of a significant but possibly short-term beneficial effect on quality of life and evidence of a beneficial effect on well-being, with the evidence described as moderate to good for both outcomes.
- Sleep and fatigue: There is moderate quality evidence to show that yoga is better for sleep problems and fatigue than no treatment.
- Psychological health: The effects of yoga on psychological health appear to be complex: yoga appears better for anxiety, depression, distress and overall mental wellbeing than psychosocial/educational interventions but no better than no treatment.
- Physical function: Effects on physical function/wellbeing were not found to be significant. The evidence also indicated that effects only occurred during the yoga intervention in most cases.
- Appetite and nausea: There is some preliminary evidence of beneficial effects on appetite and nausea but it is unclear if these are direct effects or due to improvements in other symptoms such as anxiety and sleep.
- Pain: There is no consistent evidence of effects on pain.
- Stress: Short term, beneficial effects have been reported on perceived stress.
One systematic review and a total of 8 RCTs have investigated the effects of yoga in people with cancers other than breast cancer. Most of these are small trials and the only trial with more than 70 participants included a large number of breast cancer patients along with those with other cancers. The majority of trials measure effects on a range of outcomes, many of which are subjective and self-assessed.
- Effects on sleep appear beneficial based on a large, well-conducted trial.
- Effects on anxiety appear positive in the short term based on several small RCTs.
- Effects on depression, fatigue and quality of life are unclear, with mixed results in RCTs.
- Effects on problems specific to certain cancers e.g. lung function in lung cancer, sexual function in prostate cancer are unclear based on results from single small trials.
Few adverse events are reported in clinical trials and serious adverse effects appear to be rare, based on the limited number of case reports in the literature. Overall injury rates are comparable to other exercise types. Adverse effects are particularly associated with handstands, shoulder stands and headstands and with unsupervised yoga practice. Single case reports of serious adverse events indicate that these are possible, particularly with certain practices applied too aggressively or in people with specific risk factors.
Karen Pilkington and the CAM Cancer Consortium. Yoga [online document], November 2019.
Fully revised and updated in November 2019 by Karen Pilkington.
Fully revised and updated in August 2015 by Karen Pilkington.
Summary first published in June 2013, authored by Karen Pilkington.
The word yoga derives from the Sanskrit root “yuj” which can be translated as to bind or yoke together or a 'union' and refers to the supposed union between mind, body and spirit (Feuerstein 2001). In its traditional form, yoga practice included moral disciplines in addition to physical exercises and meditation. The eight steps of Classical Yoga are yama or “restraint” or refraining from various vices, niyama or “observance” which includes contentment and tolerance, asana – the postures or physical exercises, pranayama – the breathing techniques, pratyahara which is the preparation of the mind for meditation, dharana –concentration, dhyana - meditation and samadhi or “absorption” - realization of the essential nature of the self (Taneja, 2014). Different forms of yoga exist: in the West, the most widely practised form is Hatha yoga, which includes physical postures and exercises to stretch and improve flexibility of the body, breathing exercises, relaxation and meditation (Riley 2004). Some of the more recently introduced forms of yoga include Iyengar, which is based on Hatha yoga but often makes use of props such as blocks in performing the asanas, Ashtanga or ‘power’ yoga, Vinyasa (‘flowing’ yoga) and Bikram (‘hot’ yoga performed in high temperatures and humidity) (Sovik and Bhavanani, 2016).
Application and dosage
Yoga is provided in classes led by a yoga teacher or taught on a one-to-one basis. It can also be practised by the individual having learnt the techniques in a class or from audio-visual resources such as DVDs or instruction books.
Yoga originated in Indian culture and in its original form consisted of a complex system of spiritual, moral and physical practices aimed at attaining ‘self-awareness’ (Riley 2004). The ideas surrounding yoga practice were first introduced to the West in the 1890s by a Hindu teacher, Swami Vivekananda, who toured around Europe and the USA (Feuerstein 2001). Other Indian yoga practitioners followed and, in the 1960s, interest in Hindu spirituality increased. A series of case studies were reported which focused on aspects such as heart rate and blood pressure of yoga practitioners (Wenger 1961). These were followed by early trials of yoga in the control of hypertension (Patel 1975a; Patel 1975b). Psychological aspects of long-term yoga practice were also discussed (Malhotra 1963). In the 1980s and 1990s, research published by Dean Ornish, a physician and professor at the University of California, generated further interest in yoga as a therapeutic intervention and component of a lifestyle intervention in heart disease (Ornish 1983; Ornish 1990). By 2004, trials were being conducted of yoga in a range of medical conditions (Khalsa 2004). The popularity of yoga has continued to increase, with yoga classes widely available and offering a range of variations on the original practice (Saper 2004).
Claims of efficacy and alleged indications
Yoga is used by people suffering a range of health-related problems as well as to improve general fitness levels (Saper 2004). Common uses include for the relief of stress, anxiety and depression, for chronic pain and as part of programmes such as mindfulness-based stress reduction used in cancer patients. It is widely promoted as beneficial to physical, psychological and spiritual health.
Mechanisms of action
In general terms, the asanas or stretches involve standing, bending, twisting and balancing the body leading to improved flexibility and strength. Breathing exercises and control help to focus the mind and achieve relaxation while the aim of meditation is to calm the mind (Riley 2004). The exact mechanism of action is unclear although several theories have been proposed. These include modulation of the stress response systems with consequent reduction in sympathetic tone and catecholamine levels, and reduction in activation of the hypothalamic pituitary axis. It has also been suggested practice of yoga leads to activation of antagonistic neuromuscular systems increasing the relaxation response in the neuromuscular system (Riley 2004). Meditation is thought to stimulate the limbic system and has been shown to increase blood flow to the brain and the release of endogenous dopamine, and to reduce respiratory rate. Two small studies have reported increased levels of GABA, a neurotransmitter, as a result of practising yoga asanas (Streeter 2007; Streeter 2010).
Prevalence of use
Practice of yoga is increasing in prevalence, particularly in the Western world. By 1998, an estimated 15 million adults in the USA had used yoga at least once and over 7 million had used it within the previous year (Saper 2004). Sixty four per cent used it for wellness and 48% for specific health problems. An increase in prevalence was also demonstrated between 2002 and 2007 and again between 2012 and 2017 (Barnes 2008; Barnes 2004; Clarke et al. 2018). The most recent figures indicate that yoga is the most commonly used complementary health approach among U.S. adults in 2017 (14.3%) (Clarke et al. 2018). With regard to practice in cancer patients, various figures have been reported: between 1 and 4 % of breast and gynaecological cancer patients in Europe (Molassiotis 2006a; Molassiotis 2006b) but no reported use in other cancer patients such as lung and colorectal cancer (Molassiotis 2005; Molassiotis 2006c). In the USA, up to 12 to 18% in cancer patients have been reported to practice yoga (Buettner 2006; Desai 2010) while another survey indicates that prevalence of use is 9.6% in breast cancer patients (Buffart 2012).
There is no mandatory regulation of yoga teachers in countries including the USA, Australia and Europe. Regulation of yoga teachers is currently voluntary and is provided through a number of organisations including the International Association of Yoga Therapists, the International Yoga Federation and the Yoga Alliance. In the UK, the British Council for Yoga Therapy has worked with the Complementary and Natural Healthcare Council (CNHC) which provides a mechanism for voluntary regulation of yoga therapists.
Costs and expenditures
The cost of yoga classes varies widely with typical costs in Europe (based on costs advertised on the internet in September 2019 for classes in the UK and Germany) of between 8 to 20 Euros per hour with costs increasing for one-to-one sessions.
Sixteen systematic reviews specifically of yoga in cancer have been published, which included between 1 and 24 randomised controlled trials (and a total of between 39 and 2,183 patients). The reviews are described in table 1. Differences in the number of included studies reflect differences in the inclusion criteria, search dates, whether trials were restricted to certain types of cancer and the range of outcomes covered. The 2017 Cochrane (Cramer 2017) review which assessed the effects of yoga on health-related quality of life, mental health and cancer-related symptoms in breast cancer patients included 24 trials while the corresponding Cochrane review which focused solely on patients with haematological malignancies, included only one small trial (Felbel 2004).
Note: one publication described as a systematic review is actually a narrative review (Mustian 2013a) while a second SR has only been published as a conference abstract (O’Neill 2016). Thus, neither are discussed here.
Systematic reviews of yoga in breast cancer address a wide range of outcomes. The quality of the included trials varied considerably with moderate evidence for some comparisons between yoga and no treatment and between yoga and psychosocial/educational interventions but only very low quality evidence to show that yoga may be comparable to other exercise-based interventions. There is potential for the introduction of bias, particularly when subjective outcomes are assessed by patients, as masking of treatment is impossible.
- These reviews demonstrate evidence of a significant but possibly short-term beneficial effect on quality of life and evidence of a beneficial effect on well-being, with the evidence described as moderate to good for both outcomes.
- There is also moderate quality evidence to show that yoga is better for sleep problems and fatigue than no treatment.
- The effects of yoga on psychological health appear to be complex: yoga appears better for anxiety, depression, distress and overall mental wellbeing than psychosocial/educational interventions but no better than no treatment.
- Effects on physical function/wellbeing were not found to be significant. The evidence also indicated that effects only occurred during the yoga intervention in most cases.
- There is some preliminary evidence of beneficial effects on appetite and nausea but it is unclear if these are direct effects or due to improvements in other symptoms such as anxiety and sleep.
- There is no consistent evidence of effects on pain.
- Short term, beneficial effects have been reported on perceived stress.
Ten RCTs have investigated the effects of yoga in people with cancers other than breast cancer; the trials are described in table 2. Most of these are small trials and the only trial with more than 70 participants included a large number of breast cancer patients along with those with other cancers. The majority of trials also measure effects on a range of outcomes, many of which are subjective and self-assessed.
- Effects on sleep appear beneficial based on a large, well-conducted trial.
- Effects on anxiety appear positive in the short term based on several small RCTs
- Effects on depression, fatigue and quality of life are unclear, with mixed results in RCTs
- Effects on problems specific to certain cancers e.g. lung function in lung cancer, sexual function in prostate cancer are unclear …
Breast cancer: description of studies by outcome (see Table 3)
Note: Eleven of the 16 systematic reviews reported effect sizes on specific outcomes which are discussed below. The remaining 5 systematic reviews (Harder 2012; Sadja and Mills 2013; Sharma 2013; Sharma 2016; Tolia 2018) present narrative findings of generally positive effects on a range of outcomes.
Seven systematic reviews report effects of yoga compared with control. (Lin 2011; Zhang 2012; Buffart 2012; Cramer 2012b; Felbel 2014; Cramer 2017; Pan 2017) When the comparisons with control are split according to whether no treatment or active treatment was used, a differential effect was found. For yoga compared with no treatment control, the evidence was judged to be very low quality and to show no significant difference (Cramer 2012b; 2017). While fewer trials have compared yoga with active controls such as psychotherapeutic/education interventions, the evidence overall is better quality and demonstrates a significant difference with beneficial effects due to yoga. The evidence only supports short-term effects with effect sizes of -2.21 (SMD 95% CI -3.90—0.52) reported in the Cochrane review (Cramer 2017).
The pattern for depression is similar to that for anxiety: based on the results of the seven systematic reviews (Lin 2011; Zhang 2012; Buffart 2012; Cramer 2012b; Felbel 2014; Cramer 2017; Pan 2017), yoga appears to be significantly more effective than control but there is a differential effect depending on the control. For yoga compared with no treatment control, low quality evidence showed no significant difference (Cramer 2012b; 2017). Fewer trials have compared yoga with active controls such as psychotherapeutic/education interventions but the evidence overall is better quality and demonstrates a significant difference with beneficial short-term effects due to yoga. The effect size reported in the Cochrane review is SMD -2.29 (95% CI -3.97—0.61) (Cramer 2017).
Five systematic reviews, none of which are particularly recent, have assessed effects on distress (Lin 2011; Zhang 2012; Buffart 2012; Cramer 2012b; Felbel 2014). Similar to effects on anxiety and depression, effects on distress are mixed with more positive results reported when yoga is compared with active controls than no treatment controls. An effect size of -1.55 (95% -2.48—0.61) was reported for the comparison against active control and risk of bias generally high (Cramer 2012b).
Eight systematic reviews address yoga for fatigue (Lin 2011; Zhang 2012; Cramer 2012a; Buffart 2012; Felbel 2014; Cramer 2017; Pan 2017; Dong 2019). In contrast to the effects on anxiety, depression and distress, yoga appears to be more effective than no treatment for fatigue. Effects appear to be only short-term and an effect size of -0.48 (95% CI -0.75—0.20) has been reported in the Cochrane reviews (Cramer 2017). Risk of bias is high due to lack of blinding and an outcome that is subjective and self-reported. No difference is seen between yoga and other forms of exercise.
Only one systematic review of 4 trials has attempted to assess the effects of yoga on gastro-intestinal symptoms (Pan 2017). One of the included trials was of a mindfulness programme where the specific effects of yoga are difficult to determine. In the remaining trials, appetite improved alongside distress, fatigue and sleep; nausea improved with reduction in anxiety and gastrointestinal and emotional irritability both improved concurrently. Thus, there appear to be some preliminary evidence of beneficial effects but it is not possible to conclude whether these are direct effects or due to improvements in other symptoms.
One systematic review reported on pain and included 4 trials where pain was measured as one of a number of outcomes (Pan 2017). No difference was seen between yoga and control (no treatment or brief supportive treatment). There was significant heterogeneity between the 4 studies (contrary to the statement by the review authors) and this needs further explanation.
Three older systematic reviews including only a few trials have assessed effects of yoga on stress in breast cancer patients (Lin 2011; Zhang 2012; Cramer 2012b). These suggest a short-term benefit but effect sizes vary and further evidence is required for firm conclusions.
No significant effects on physical health have been reported in 4 systematic reviews (Lin 2011; Buffart 2012; Cramer 2012b; Pan 2017) of yoga for breast cancer patients. Risk of bias was judged to be generally high (Cramer 2012b)
Quality of life
Seven systematic reviews have assessed effects on quality of life (Lin 2011; Zhang 2012; Buffart 2012; Cramer 2012b; Cramer 2017; Pan 2017; El-Hashimi 2019). Overall, a beneficial effect of yoga is reported when yoga is compared with no treatment. The Cochrane review, which included the largest number of RCTs, concluded that there is moderate quality evidence of a beneficial effect on quality of life of breast cancer patients with an effect size of 0.22 (95%CI 0.04-0.4)(Cramer 2017). The effects appear to be short-term although few trials have carried out longer-term assessment.
Six systematic reviews have reviewed effects of yoga on sleep. Effects are mixed with several reporting no difference (Zhang et al 2012; Buffart 2012; Felbel 2014; Cramer 2017; Pan 2017; Tang 2019). Short term benefits on sleep are seen in breast cancer patients when yoga is compared with no treatment according to the Cochrane review (SMD -0.25 95% CI -0.04- -0.09) (Cramer 2017). The evidence is judged to be moderate quality but there is little evidence comparing yoga with active controls on sleep. When yoga was compared with walking, regular moderate intensity walking appeared to have a more positive effect (Tang 2019).
Wellbeing (emotional, functional, social, spiritual)
Two older systematic reviews have reported positive effects are reported on various aspects of wellbeing (Buffart 2012; Cramer 2012b). Significant differences of 0.3-0.5 for the majority of aspects based on small numbers of RCTs. No difference was seen in mental wellbeing when yoga is compared against no treatment. The reasons for this inconsistency are unclear and wellbeing has not been assessed in recent systematic reviews.
Clinical guidelines on yoga in breast cancer
The Society for Integrative Oncology (SIO) has produced evidence-based guidelines on use of integrative therapies during and after breast cancer treatment (Greenlee et al. 2017). These have been endorsed by the American Society of Clinical Oncology (Lyman et al. 2018) . The SIO guidelines are based on a systematic review of RCTs published up to 2015 and the recommendations for yoga are as follows:
- is recommended for reducing anxiety. (Grade B)
- is recommended for improving mood disturbance and depressive symptoms. (Grade B)
- can be considered for improving post-treatment fatigue. (Grade C)
- is recommended for improving quality of life. (Grade B)
- (Gentle yoga) can be considered for improving sleep. (Grade C)
Note on evidence grading:
B Recommends the modality (there is high certainty that the net benefit is moderate, or there is moderate certainty that the net benefit is moderate to substantial—offer/provide this modality).
C Recommends selectively offering or providing this service to individual patients based on professional judgment and patient preferences (there is at least moderate certainty that the net benefit is small—offer/provide this modality for selected patients, depending on individual circumstances).
A Cochrane review of yoga for haematological malignancies (Felbel 2014) found only one small trial in 39 people with Hodgkin or non-Hodgkin's lymphoma. (Cohen 2004 – see RCT Table) This trial compared Tibetan yoga plus standard care against standard care alone; it was assessed as being of high risk of bias.
Only four other RCTs in patients with other types of cancer were included in the systematic reviews: three in mixed cancer types and one in colorectal cancer. In two of the trials in mixed cancer types, yoga was part of a mindfulness programme (mindfulness-based art therapy and mindfulness-based stress reduction). The specific effects of yoga are difficult to determine when part of a complex intervention and the trials will not be considered further here. One RCT which did focus on yoga was a large, multicentre, trial that investigated the effects of yoga compared with standard care on sleep quality in post-treatment cancer survivors (Mustian 2013b). A smaller trial recruited 54 people with non-metastatic colorectal cancer who attended weekly yoga for 10 weeks or joined a waitlist control group. (Cramer 2016).
Several small RCTs suggest that yoga has beneficial effects on anxiety for patients with a range of cancers (Hardoerfer 2018; Adair 2018; Cramer 2016; Huberty 2019). In one trial, a positive effect was only seen at week 10 of the intervention. Another trial found no effect on state anxiety (Cohen 2004).
Mixed effects are reported on depression: one RCT reported positive effects (Huberty 2019), in another trial positive effects were seen only at 10 weeks (Cramer 2016) and 2 RCTs found no significant difference between yoga and control groups (Cohen 2004; Hardoerfer 2018),
Secondary analysis of results from a large RCT indicated beneficial effects on fatigue in 97 people who were cancer survivors (Sprod 2015) while less fatigue was also seen in prostate cancer patients who practised yoga in a small trial (Ben-Josef 2017). A trial in people with lymphoma and one in people with various cancers found no significant difference for yoga (Cohen 2004; Hardoerfer 2018).
Beneficial effects on pain and range of shoulder motion have been reported in a small RCT involving 40 head and neck cancer patients (Adair 2018). A trial of online yoga in 62 myeloproliferative neoplasm patients resulted in small/moderate effects on pain (Huberty 2019).
Quality of life
A small trial that recruited 54 people with non-metastatic colorectal cancer who attended weekly yoga for 10 weeks or joined a waitlist control group. (Cramer 2016). No effects of yoga on health-related quality of life were found but the trial was affected by low intervention adherence (patients attended a mean of 5.3 of the 10 classes) and a high attrition rate. No adverse effects were reported. Another RCT in prostate cancer patients did not demonstrate a significant effect (Ben-Josef 2017).
A large, multicentre, trial investigated the effects of yoga compared with standard care on sleep quality in 410 post-treatment cancer survivors (Mustian 2013b). Patients had been treated for gastrointestinal, gynaecologic, haematological and other cancers although the majority were breast cancer survivors. The trial was rigorous in design and subjective assessment of sleep quality was supplemented with sleep actigraphy. Beneficial effects on sleep quality were reported in the group attending yoga classes twice weekly as well as receiving standard care compared with those who received only standard care. No serious adverse events related to yoga were reported. These beneficial effects are similar to those reported in an earlier, small trial in lymphoma patients (Cohen 2004).
One small RCT in 32 lung cancer patients reported short-term improvement in lung function due to yoga breathing but non-significant differences between yoga breathing and standard breathing for the majority of physiological measures. This may be due to the lack of power of the study (Barassi 2018) Secondary analysis of data from 328 participants in a large RCT on sleep suggested beneficial effects of yoga practice on memory difficulties (Janelsins 2016)
Other secondary outcomes assessed in RCTs of yoga in cancer patients include erectile dysfunction and urinary incontinence in the RCT involving 68 prostate cancer patients (Ben-Josef 2017). Sexual function and total symptom burden were also measured in a trial in 62 myeloproliferative neoplasm patients (Huberty 2019). In both trials, effects on these outcomes were small and not consistent over time.
Few adverse effects were reported in the clinical trials but participants do undergo screening prior to participation and, based on the breast cancer trials included in the Cochrane review, the mean age of participants ranged from 44.0 to 62.9 years but in the majority (all except 2 trials), mean age was below 60 years of age (Cramer 2017).
Several case reports of adverse psychological effects have been published but these appear to be related specifically to meditation (Kirkwood 2005). Other single case reports indicate that serious adverse events are possible, particularly with certain practices applied too aggressively. For example, spontaneous pneumothorax was observed in a patient following practice of Kapalabhati pranayama, a common breathing exercise (Johnson 2004). Certain postures such as headstands and the lotus position have also been associated reports of adverse effects in individuals. For example, sciatic nerve damage in a 67 year old woman (Dacci 2013), damage to a knee ligament when attempting an advanced stretch (Patel 2008), eye-related problems in individuals with existing risk factors, for example a patient with glaucoma practising headstands (De Barros 2008) and headstands linked to spinal compression in a patient with myelomalacia, a spinal condition (Ferreira 2016). Adverse events do appear to be rare based on the limited number of case reports in the literature but these indicate that certain practices may be not be advisable in individuals with existing risk factors.
A cross-sectional survey of over 1,700 yoga practitioners in Germany found that 1 in 5 adult yoga users reported at least one acute adverse effect in their yoga practice, and one in ten reported at least one chronic adverse effect, mainly musculoskeletal effects (Cramer 2019). Adverse effects were particularly associated with handstands, shoulder stands and headstands and with unsupervised yoga practice. Over 75% fully recovered. Overall injury rates were comparable to other exercise types, a similar finding to that reported in a systematic review of 301 RCTs of yoga. (Cramer 2015) However, this review did highlight a lack of reporting on safety in a significant number of trials so that adverse events may be underreported and any risks are difficult to assess conclusively.
Contraindications and warnings
Caution, including avoidance of specific postures such as inverted postures, has been suggested in pregnancy and in individuals with hypertension, although this appears to be based on likely risk (MSKCC 2019). It has also been suggested that breathing exercises particularly if vigorous could potentially exacerbate asthma and other respiratory problems. Again this is based on theoretical risk and occasional case reports such as those above. Other conditions may require caution or the avoidance of specific practices and the advice of the primary healthcare professional and the yoga instructor prior to undertaking yoga.
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