As Americans become increasingly interested in the preventive and therapeutic benefits of alternative and complementary medicine, researchers are responding by attempting to quantify the role of yoga in the treatment and prevention of specific diseases and health conditions.
As fitness and mind-body professionals, we strive to find valid scientific research behind any recommendations we make to our clients. This is especially true about yoga, which generates many questions from consumers. Does the available research on yoga substantiate the health claims? Read on to learn how to separate fact from fiction when it comes to yoga research and any health benefits associated with yoga.
History of Yoga Research
Although yoga has been practiced for centuries in other parts of the world, most of the theory behind the practice has not yet been systematically studied using the rigorous tools of modern medical science. In the past several years, the scientific community has begun in earnest to seek out answers to some of the questions about yoga’s efficacy as treatment for disease. However, as research on yoga begins to uncover some potential therapeutic benefits of yoga, the studies also underscore the inherent difficulties of systematically evaluating this multifaceted and holistic practice.
Granted, it is exciting to see a growing body of scientific research supporting the positive effects of practicing yoga. Nonetheless, it is important to recognize that not all yoga research studies are created equal. Before examining the most compelling yoga research findings, it is valuable to understand the key components that constitute a scientifically valid study. These components are explained in the sidebar “Factors That Affect Scientific Research Studies.”
Good Scientific Evidence
Despite the challenges of researching the health benefits of yoga, many good-quality studies are beginning to emerge, and the results are interesting. The following sections describe some of the findings of “good” studies, meaning that researchers have made some attempt to utilize the elements of scientific research outlined in the “Factors That Affect Scientific Research Studies” sidebar. Also presented in the sections that follow are tips on what to tell clients about the findings.
Back pain is a common condition that can negatively affect one’s quality of life. Can a regular yoga practice help prevent or treat back pain?
The Research. A randomized controlled trial (RCT) involving 101 patients with chronic low-back pain compared a viniyoga practice with conventional back exercise classes and with use of a self-help book. During the 12-week intervention, an instructor taught a weekly 75-minute viniyoga practice for the yoga treatment group, who also received handouts and an audio CD guide for home practice. At the end of the 12 weeks, the yoga group showed more improvement in back function than the two control groups, who either participated in the conventional exercise classes or were given the self-help book (Sherman et al. 2005).
The Take-Home Message. A regular practice of specific viniyoga poses has been shown to improve certain symptoms of back pain.
What to Tell Your Clients. Clients with routine back strain should practice yoga gently and should not attempt poses that require extreme twisting or vigorous spinal extension, as these exercises can put a lot of strain on the spinal disks and nerve roots, potentially causing a ruptured disk. Anyone who has severe or worsening back pain, traumatic back injury or loss of lower-body sensation or function during or after a yoga session should be evaluated by a physician.
Carpal tunnel syndrome is a common wrist compression neuropathy that causes pain, paresthesia (a burning or tingling sensation) and disability. Is yoga an effective therapy for this increasingly common syndrome?
The Research. In a randomized, single-blind controlled trial, 42 carpal tunnel patients were assigned to one of two groups for an 8-week period. One group performed yoga, while the second group wore wrist splints. Twice a week, the yoga group practiced postures specifically designed for the upper body. At the end of the study period, the yoga participants showed improvement in grip strength, pain levels and elicited symptoms compared with the wrist splint group. Unfortunately, this study’s design flaws included a small sample size, a short treatment period and a lack of objective testing on the groups at the study’s conclusion (Garfinkel et al. 1998).
Other researchers reviewed 21 separate trials that evaluated the clinical outcome of nonsurgical treatments for carpal tunnel syndrome. After 8 weeks of yoga, participants had significantly reduced pain compared with other participants who wore wrist splints (O’Connor, Marshall & Massy-Westropp 2003). The researchers concluded that yoga provided a “significant short-term benefit” for people with carpal tunnel syndrome (O’Connor, Marshall & Massy-Westropp 2003).
The Take-Home Message. A regular practice of specific yoga poses with a focus on the upper body has been shown to improve some symptoms of carpal tunnel syndrome.
What to Tell Your Clients. People who suffer from carpal tunnel syndrome should modify poses as needed to avoid wrist strain. Poses that cause numbness, tingling or exacerbation of symptoms should also be avoided. Some poses can be modified by using different hand positions to minimize wrist pressure. For example, downward-facing dog can be modified by resting the upper-body weight on the forearms instead of the hands.
As Baby Boomers age, more and more of them will likely suffer from the debilitating effects of osteoarthritis (OA). Since OA is a common problem in the United States, many people would benefit from an exercise program that could mitigate the symptoms of this condition. Would yoga be a good option for clients with OA?
The Research. In one pilot study, 11 deconditioned subjects who had been clinically diagnosed with OA in the knee experienced some relief from symptoms once they started a yoga program. After 8 weeks in a modified Iyengar yoga class that met just once per week, all of the subjects showed a reduction in knee pain stiffness (Kolasinski et al. 2005).
The Take-Home Message. Although this was a small study, the results suggest that yoga may help relieve some common symptoms of OA. Some clients with OA may need to modify certain yoga poses and may benefit from the assistance of props, such as blocks, blankets or a yoga strap.
What to Tell Your Clients. More studies are needed to compare the effectiveness of yoga with that of conventional therapies in mitigating the symptoms of OA. However, a regular modified yoga practice may be helpful for this condition. Any client who experiences arthritis pain accompanied by joint swelling needs prompt medical evaluation.
The principle of specificity in exercise science holds that a healthy body will adapt to the specific physical stressors placed upon it. With yoga’s heavy emphasis on correct biomechanics and muscle stretching and strengthening, it is not surprising that some of the strongest evidence of the benefits of yoga has come from studies that measured strength and flexibility indices.
The Research. Researchers who examined the fitness-related benefits of hatha yoga studied 10 previously untrained subjects who had no knowledge of yoga (Tran et al. 2001). The subjects participated in twice-weekly sessions of yoga breathing exercises and hatha yoga. After 8 weeks, the subjects showed significant improvements in upper- and lower-body muscular strength, endurance and flexibility; there was no statistically significant change in body composition or pulmonary function (Tran et al. 2001). Unfortunately, this trial lacked a control group, had a relatively short training period and drew from a small, homogeneous sample (Tran et al. 2001).
Another study compared subjects who performed an average of about 21 hours of hatha yoga classes with a sedentary control group (Boehde et al. 2005). At the end of the 8-week study period, the yoga group showed significant improvements in flexibility, balance and muscular endurance compared with the controls (Boehde et al. 2005).
The Take-Home Message. A regular yoga training program appears to improve balance, along with muscular flexibility, strength and endurance.
What to Tell Your Clients. Yoga can improve balance, along with muscular flexibility, strength and endurance, which can have a positive carryover effect on the activities of daily living and sports participation.
Promising Scientific Evidence
The following sections describe the findings of yoga research studies that, while promising, did not adhere to the strict elements of scientific research. As a result, any findings need to be replicated through more stringent studies in the future.
More and more children in the United States are being diagnosed with attention deficit disorder (ADD) or attention deficit disorder with hyperactivity (ADHD). The hallmarks of these disorders include an inability to stay attentive and increased impulsivity, often accompanied by hyperactivity, which can have a profound effect on a child’s education and family interactions. Would yoga be useful for children who suffer from these conditions?
The Research. Researchers studied 19 boys who had been clinically diagnosed with ADHD and randomly assigned them to either a yoga treatment group or a cooperative activities group (Jensen & Kenny 2004). Although both groups of boys showed improvement in certain measured behaviors, the yoga group had more favorable changes in factors such as emotional liability, restlessness and impulsive behavior. Subjects who participated in additional home practice of yoga showed an even greater response (Jensen & Kenny 2004).
The Take-Home Message. This was a pilot study with a very small sample size. However, the findings do suggest that yoga may be a good adjunct treatment for children with ADD/ADHD who are already stable on medication.
What to Tell Your Clients. Yoga may be a useful tool to help manage the behaviors associated with ADD/ADHD, particularly during those periods when medication effects are wearing off or patients are taking a scheduled medication-free period.
The very idea of yoga invokes an image of peace and tranquility. In fact, many media portrayals of yoga use a photo image of a person who appears to be in a state of higher consciousness, clearly free from mental stress and anxiety. Can yoga really help us achieve this blissful state?
The Research. In one meta-analysis, researchers reviewed the findings of eight separate studies that involved yoga interventions in subjects suffering from anxiety and related disorders (Kirkwood et al. 2005). The most positive results of the yoga interventions were reported in cases involving subjects with obsessive-compulsive disorder (OCD). Unfortunately, the eight studies under review were marred by poor research techniques and methodological inadequacies, which made it difficult for the researchers to compare the different studies (Kirkwood et al. 2005). Another study, which compared two separate RCTs, investigated the effectiveness of meditation and yoga on patients with diagnosed anxiety disorders (Krisanaprakornkit et al. 2006). After analyzing the results of the two studies, the researchers were unable to draw distinct conclusions about yoga’s effect on anxiety disorders because they did not find any correlation between the activity and any reduction in objective measurements of anxiety. However, the researchers did say that additional well-conducted research was warranted (Krisanaprakornkit et al. 2006).
The Take-Home Message. Yoga may help clients with OCD and anxiety, but better research is warranted before definitive recommendations can be made.
What to Tell Your Clients. Yoga has not been shown to make anxiety worse, and it might help alleviate symptoms of anxiety and OCD. Worsening anxiety or behavioral issues should be evaluated by a mental health professional.
According to the Centers for Disease Control and Prevention, cardiovascular disease (CVD) is the number-one cause of death in the United States (www.cdc.gov/nchs/fastats/death.htm). If yoga could reduce the risk of CVD, could this practice change the way the medical community treats these patients?
The Research. A recent systematic literature review of 70 studies on yoga therapy showed a trend toward beneficial changes in CVD risk factors, such as insulin resistance, lipid profiles and blood pressure (Innes, Bourguignon & Taylor 2005). Although one-third of the studies reviewed were RCTs, the majority of the studies were plagued by poor design and other factors that confounded the researchers’ interpretations (Innes, Bourguignon & Taylor 2005). Another comprehensive review of the literature on the psychophysiologic effects of yoga concluded that a regular hatha yoga practice and a “yoga lifestyle” might reduce other CVD risk factors, such as insulin sensitivity or lipid profiles (Raub 2002).
The Take-Home Message. Preliminary studies suggest that yoga could play a role in improving CVD risk. However, more rigorously controlled research is needed before any specific conclusions can be drawn.
What to Tell Your Clients. Yoga practice can be part of a healthy lifestyle, but it has not yet been “proven” to reduce CVD risk directly.
Although the jury is still out on whether yoga can reduce the risk of CVD, might it not be beneficial for improving cardiovascular fitness in general? Many practitioners claim that yoga is their sole form of exercise for staying fit. But can yoga really improve cardiovascular fitness?
The Research. According to some experts, a typical hatha yoga routine burns 2.2–3.6 kilocalories per minute—the equivalent to what is burned during a slow walk (Clay et al. 2005). Except in the case of extremely deconditioned clients, this “gentler” form of yoga alone is unlikely to confer significant improvements in cardiovascular fitness, pulmonary function, body composition or fat metabolism (Tran et al. 2001).
The Take-Home Message. The general consensus among experts is that a typical hatha yoga practice does not provide the stimulus necessary to enhance cardiovascular endurance. However, more vigorous forms of yoga that require a higher energy output could hold more promise for improving overall cardiovascular fitness.
What to Tell Your Clients. Yoga does not appear to improve cardiovascular fitness to the same degree as conventional cardiovascular exercise because not as many calories are expended during a yoga session.
Depression is a common mood disorder characterized by feelings of guilt, hopelessness and worthlessness. Can yoga be used as an accessible, low-cost adjunct therapy to conventional treatments for clients who suffer from this often-debilitating condition?
The Research. A review of five different RCTs evaluated yoga-based interventions for depression and depressive disorders (Pilkington et al. 2005). For mild to severe depressive disorders, the researchers reported some positive outcomes and no adverse effects from the yoga interventions. But the studies they reviewed were poorly designed and contained incomplete methodological reporting (Pilkington et al. 2005). In another RCT, researchers compared breast cancer survivors who completed 7 weeks of yoga training with controls who did not take part in the training (Culos-Reed et al. 2006). At the end of the study, the researchers reported positive changes in the yoga subjects’ emotional function, depression and mood disturbance (Culos-Reed et al. 2006).
The Take-Home Message. Yoga practice may help clients with depressive disorders and stressors, but more research is warranted before definitive recommendations can be made.
What to Tell Your Clients. Yoga has not been shown to make depression worse, and a regular practice might help alleviate certain symptoms. In the case of worsening depression, suicidal ideation or major depressive disorder, a mental health professional’s evaluation is required.
Irritable bowel syndrome (IBS) is a functional disorder of the colon that causes abdominal pain, pressure, bloating and constipation or diarrhea. Would yoga be a useful tool for managing these common IBS symptoms?
The Research. An RCT observed a small sample of patients who had been clinically diagnosed with IBS (Taneja et al. 2004). For 2 months, one group was given drug treatment while the other group practiced yoga twice a day. Both groups demonstrated a decrease in bowel symptoms and anxiety, but no definitive or statistically significant improvement in symptoms could be attributed to the yoga practice (Taneja et al. 2004).
The Take-Home Message. Yoga might be a beneficial adjunct therapy to help patients manage IBS symptoms, but larger study sample sizes are warranted before a conclusion can be drawn.
What to Tell Your Clients. Yoga may have a beneficial effect on IBS discomfort and on the anxiety that tends to exacerbate symptoms. Clients with worsening abdominal pain or changes in symptoms should receive prompt medical evaluation from their physician.
Findings from the Women’s Health Initiative led researchers in 2002 to take an unprecedented stand in halting the study when it became clear that the CVD risks to women taking long-term hormone replacement therapy outweighed the benefits. As a result, many postmenopausal women have chosen not to take hormone replacement therapy and instead are now seeking nonhormonal methods to control common menopausal symptoms, such as hot flashes and impaired sleep patterns.
The Research. A small pilot study of 14 postmenopausal women examined whether 8 weeks of “restorative” yoga had any effect on the severity and frequency of hot flashes (Cohen et al. 2007). Although the women did report that their hot flashes
decreased in severity and frequency, this trial had no control group or objective evaluation (Cohen et al. 2007). Other
researchers conducted an RCT that studied sleep quality in 164 postmenopausal women (Elavsky & McAuley 2007). The
subjects were randomly divided into three groups: a low-
intensity yoga class; a moderate-intensity walking program; and a control group. After 4 months, the researchers saw no statistically significant interventional effects on total sleep quality from any of the three treatments (Elavsky & McAuley 2007).
The Take-Home Message. A low-intensity yoga practice may help decrease the perceived severity and duration of hot flashes, but to date, it has not been shown to influence sleep quality.
What to Tell Your Clients. A gentle yoga practice may be part of an overall lifestyle approach that can help decrease the discomfort of some menopause symptoms.
Wrapping It Up
At this time, the available body of scientific research on yoga as therapy for certain health conditions does not support any specific conclusions about yoga’s practical application in disease prevention or treatment.
The good news is that there is now a push within the medical and scientific communities to design and support more rigorous studies of yoga’s therapeutic role. For those who want more information on yoga research studies in the pipeline, the National Institutes of Health’s National Center for Complementary and Alternative Medicine has a large database of ongoing and future studies evaluating yoga’s role in disease prevention (http://nccam.nih.gov/
In the meantime, there seems to be some consensus that a properly executed yoga practice may be an effective adjunct therapy to conventional medical treatment for certain conditions, such as back pain, knee osteoarthritis and carpal tunnel syndrome. It also appears to be effective at improving balance, flexibility and muscle endurance. The possibilities are very exciting about the effect of yoga on other conditions, but more studies are needed before any specific recommendations can be made.
Additional Yoga Research Resources
- National Institutes of Health’s National Center for Complementary and Alternative Medicine (NCCAM), http://nccam.nih.gov/clinicaltrials/
alltrials.htm. The center provides information on ongoing clinical trials involving yoga and other alternative therapies.
- National Center for Biotechnology Information, www.ncbi.nlm.nih
.gov/sites/entrez. PubMed is a service of the U.S. National Library of Medicine that includes more than 17 million citations from MEDLINE and other life science journals for biomedical articles back to the 1950s.
- Open Mind Open Body, www.openmindbody.com/yogaresearch.html. Kelly McGonigal, PhD, provides a summary and interpretation of research on yoga and health.
- International Association of Yoga Therapists (IAYT), www.iayt.org. IAYT hosts a symposium on yoga therapy and research and also offers teacher resources and a peer-reviewed journal.
SIDEBAR: Factors That Affect Scientific Research Studies
Before examining any yoga research findings, you need tounderstand the essential components that constitute a scientifically validstudy. This will enable you to critically evaluate the findings and determinewhether a yoga research study is in keeping with the rigorous standards set by the scientificcommunity.
The gold standard ofreliability in clinical research is what is known as the randomized controlledtrial, or RCT. In an RCT, researchers randomly select subjects who areage- an gender matched. Participants are then randomly assigned to receive oneof several (two-three) treatment regimens or assigned to a control regimen. Thecontrol group is given a standard, established therapeutic modality; a placebo, or “sham”treatment; or no treatment at all. The most powerful RCTs are double-blind innature, which means that neither the study subjects nor the researchers knowwho is getting what treatment.
A variety of issues must beaddressed when using science to study the effects of yoga practice. Here aresome of the most important of these issues:
SampleSize. The results of studies that examine the effects of a treatment ona smallgroup of people are not generally considered to be applicable to an entirepopulation. Small sample sizes tend to be unable to detect subtle treatmenteffects. Systematic study of a large population of people is likely to give themost reliable results. Most of the studies published about yoga aresignificantly underpowered, with sample sizes comprising fewer than 100participants.
PlaceboEffect. It is well established that a subject’s own belief that atreatment is going to work can have a powerful and measurable effect on theoutcome of any study. It is impossible to “treat” a group of yoga subjects andavoid this placebo effect, since the practitioners are aware of the fact thatthey are doing yoga.
SampleBias. The RCT prefers to study a random population sample in order tominimize variables that might influence study outcomes. Many yoga studiesrecruit subjects from a yoga school or an ashram, which can lead to an inherentbias in the study group, as the subjects are not randomly selected.
Lengthof Treatment. In many of the yoga studies conducted to date, conclusionsabout the effects or outcomes of a yoga practice have been drawn after an 8- to12-week period of yoga “treatment.” Yoga practice may, in fact, take asignificantly longer time period than this to make a difference.
Consistencyof Treatment. The “treatment” under study should be consistent andsimilar each time it is administered, in order to control variability, whichcould skew results. As many yoga participants and teachers know, severalvariables can affect a yoga practice. For instance, most studies involving yogado not enumerate the poses that were utilized, how long they were held or whichstyle of yoga was emphasized. This makes reproducing results impossible.
Holisticvs. Scientific. Yoga is a multifaceted discipline, and the physicalposes are just one aspect of a yoga practice. Many practitioners believe thatscientifically quantifying the holistic changes that yoga practice may produceis impossible when you reduce the practice to a sequence of poses and studyphysical change.
Clay, C.C., et al. 2005. The metabolic cost of hatha yoga. The Journal of Strength & Conditioning Research, 19 (3), 604–10.
Cohen, B.E., et al. 2007. Feasibility and acceptability of restorative yoga for treatment of hot flushes: A pilot trial. Maturitas, 56 (2), 198–204.
Culos-Reed, S.N., et al. 2006. A pilot study of yoga for breast cancer survivors: Physical and psychological benefits. Psychooncology, 15 (10), 891–97.
Elavsky, S., & McAuley, E. 2007. Lack of perceived sleep improvement after 4-month structured exercise programs. Menopause, May-June, 535–40.
Garfinkel, M.S., et al. 1998. Yoga-based intervention for carpal tunnel syndrome: A randomized trial. The Journal of the American Medical Association, 280 (18), 1601–1603.
Innes, K.E., Bourguignon, C., & Taylor, A.G. 2005. Risk indices associated with the insulin resistance syndrome, cardiovascular disease, and possible protection with yoga: A systematic review. Journal of the American Board of Family Practitioners, 18 (6), 491–519.
Jensen, P.S., & Kenny, D.T. 2004. The effects of yoga on the attention and behavior of boys with attention-deficit/hyperactivity disorder (ADHD). Journal of Attention Disorders, 7 (4), 205–16.
Kirkwood, G., et al. 2005. Yoga for anxiety: A systematic review of the research evidence. British Journal of Sports Medicine, 39 (12), 884–91.
Kolasinski, S.L., et al. 2005. Iyengar yoga for treating symptoms of osteoarthritis of the knees: A pilot study. Journal of Alternative and Complementary Medicine, 11 (4), 689–93.
Krisanaprakornkit, T., 2006. Meditation therapy for anxiety disorders. Cochrane Database Systematic Reviews (1), CD004998.
O’Connor, D., Marshall, S., & Massy-Westropp, N. 2003. Non-surgical treatment (other than steroid injection) for carpal tunnel syndrome. Cochrane Database Systematic Reviews, (1), CD003219.
Pilkington, K., et al. 2005. Yoga for depression: The research evidence. Journal of Affective Disorders, 89 (1–3), 13–24.
Raub, J.A. 2002. Psychophysiologic effects of Hatha Yoga on musculoskeletal and cardiopulmonary function: A literature review. Journal of Alternative and Complementary Medicine, 8 (6), 797–12.
Sherman, K.J., et al. 2005. Comparing yoga, exercise, and a self-care book for chronic low back pain: A randomized, controlled trial. Annals of Internal Medicine, 143 (12), 849–56.
Taneja, I., et al. 2004. Yogic versus conventional treatment in diarrhea-predominant irritable bowel syndrome: A randomized control study. Applied Psychophysiological Biofeedback, 29 (1), 19–33.
Tran, M.D., et al. 2001. Effects of Hatha Yoga practice on the health-related aspects of physical fitness. Preventive Cardiology, 4 (4), 165–70.
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