Yoga, of which there are numerous types, is an increasingly popular mind-body intervention for select pain conditions. The modality consists of specific physical postures, breathing techniques, and mental concentration or meditation exercises. A number of clinical studies have examined the benefits of yoga as an adjunct for chronic pain management, but until now there has not been a meta-analysis of results examining the relief of pain and associated disability. While, in principle, yoga may be a useful supportive intervention for many pain-associated conditions, a closer look reveals that current research is largely inadequate and potential harms of yoga need cautious consideration.
For their meta-analysis, researchers at the University of Witten/Herdecke, Herdecke, Germany, searched databases through January 2010 for controlled clinical trials of yoga and examined efficacy outcomes of the interventions [Büssing et al. 2012]. The search uncovered 16 qualifying studies, of which 5 were of high quality, 7 had moderate quality, and 4 nonrandomized, non-blinded trials were of low quality.
Furthermore, writing in the January edition of the Journal of Pain, the authors describe a high degree of heterogeneity (ie, diversity) among the included studies:
- Yoga was variously used to treat patients with back pain (6 studies), rheumatoid arthritis (2 studies), and headache/migraine (2 studies). Three studies separately enrolled individuals for other indications — either muscle soreness, carpal tunnel syndrome, or irritable bowel syndrome — and an additional 3 enrolled otherwise healthy patients who were either personal computer users, pregnant women, or patients undergoing hemodialysis.
- Total numbers of enrolled participants in each study varied considerably from 12 to 291 (mean = 63), and only one study (the one with 291 subjects) enrolled >100 individuals.
- Four studies were characterized as short-term (up to 4 weeks), 7 as medium-term (6-10 weeks), and 5 as long-term (12-24 weeks).
- Most studies included subjects aged ≤ 50 years; however, one study enrolled only adolescents, and only one study included older patients >56 years of age.
- Control-group conditions included being on a waiting-list, physical activity and lectures, routine care, or anti-inflammatory drugs.
The researchers reported that combined data for all studies found positive effects favoring yoga interventions. With respect to relieving pain, a random-effects meta-analysis estimated a moderately large and significant overall treatment effect for yoga (Standardized Mean Difference, or SMD = 0.74; 95% Confidence Interval, CI: 0.52 to 0.97; P < 0.0001). The overall treatment effect for ameliorating pain-related disability was similarly large and favorable (SMD = 0.79; CI: 0.56 to 1.02; P < 0.0001). A subanalysis of 6 studies found a moderately favorable effect size for improvement of patients’ mood (SMD = 0.65; CI: 0.42 to 0.89; P < 0.0001). [For a discussion of effect sizes and their interpretation, see earlier UPDATE here.]
Overall, larger effect sizes for pain relief were found in studies with higher methodological quality, passive waiting-list control condition, and studies enrolling essentially healthy individuals. The strongest effects on pain-related disability were observed in studies with a shorter duration. However, for both pain and disability analyses there was a considerable amount of heterogeneity in the data; I^2-index of diversity = 44% and 54%, respectively.
The researchers conclude that, despite some limitations, their meta-analysis suggests that yoga is a useful supplementary approach with at least moderate effect sizes for relieving pain and disability associated with several chronic pain disorders. Moreover, there are hints in the data that even short-term yoga interventions might be of benefit in some cases. Nevertheless, they concede, larger-scale trials are needed to identify which patients may benefit most.
COMMENTARY: Yoga May Be Useful For Some But Not Safe For All
Meta-analysis generally yields a high level of evidence that can be helpful for guiding clinical practice in pain management. It is a statistical technique in which the outcomes of multiple studies are mathematically standardized and combined to improve the accuracy and reliability of results. Meta-analysis usually is far more important for clinical decision-making than even the best-designed individual study, but it also has some important limitations and biases — even a good meta-analysis of poor-quality or highly diverse studies will still result in bad data representing invalid outcomes.
An important criterion is that the studies available and selected for inclusion in a meta-analysis must be sufficiently similar to appropriately combine their results and arrive at both statistically and clinically valid conclusions. The analysis by Büssing and colleagues included a quite diverse, or heterogenous, collection of yoga studies in terms of pain conditions, design quality, intervention duration, group sizes (mostly underpowered) and control-group conditions, patient age, type of yoga instruction, and other variables. Many of these factors might skew or bias overall outcomes in favor of yoga. Therefore, one must be cautious in accepting the effect sizes as being externally valid for all patients with chronic pain or, even selectively, in those with back pain, headache, or arthritis for which there were multiple studies included in the analysis.
The researchers contend that beneficial effects of yoga can be explained, in principle, “by an increased physical flexibility, coordination, and strength, by calming and focusing the mind to develop greater awareness and diminish anxiety, reduction of distress, improvement of mood, etc.” We have previously reported on relatively recent studies of yoga for back pain [here and here] as compared with usual medical care or self-care, and yoga compared with simple stretching exercises [here]. Overall, the studies showed that yoga in appropriately selected patients may provide both short- and longer-term benefits in terms of pain relief and improved functionality.
However, those studies also demonstrated that yoga is not completely without risks of adverse effects, such as temporary increases in pain, and some patients might achieve only modest gains in functionality without associated reductions in pain. Büssing et al. did not assess reported adverse effects of yoga in the studies included in their meta-analysis and this could be an important omission.
A recent, and somewhat sensational, article in The New York Times Magazine — “How Yoga Can Wreck Your Body,” January 5, 2012 [here] — points to potentially devastating harms of yoga among persons who receive improper instruction, push themselves too far and/or too fast, and otherwise approach this discipline without the caution it merits. While devotees of yoga attest to its miraculous powers of renewal and healing, according to the article even yoga teachers have suffered debilitating body injuries and brain damage due to the rigorous demands of certain postures and movements.
The message to healthcare providers, from the research evidence and other sources, appears to be that yoga may be a somewhat useful adjunct to comprehensive pain care in select patients; however, at the least, patients need to be physically capable of the necessary exertion, have appropriate motivation, and receive expert guidance in the pursuit of this activity. Rather than merely casually suggesting yoga as an option to patients with chronic pain, healthcare professionals also should be familiar with locally available yoga instructors — including their credentials and the safety of their methods — to whom patients might be specifically referred.
REFERENCE: Büssing A, Ostermann T, R Lüdtke, Michalsen A. Effects of Yoga Interventions on Pain and Pain-Associated Disability: A Meta-Analysis. J Pain. 2012(Jan);13(1):1-9 [abstract here].