 Let's say you're trying to find some solid information about a serious health problem that concerns you, high blood pressure, diabetes, yet everywhere you look someone's trying to sell you something like vitamins, yoga mats, blenders, drugs, well, breathe a sigh relief because all we bring you are the facts. Welcome to the Nutrition Facts Podcast. I'm your host, Dr. Michael Greger. Today, we continue with part two of our series on yoga, and we start with the question, which of the 50 yoga styles have been shown to be best? Should doctors recommend their patients do yoga? The difficulties associated with recommending yoga stem from the low quality of scientific evidence available regarding its effects. Oddly, this lack of evidence is partly due to a common failure among researchers to define what they actually study. They just say yoga without defining what they mean, and different types of yoga differ greatly in what they demand in terms of physical strength, depth of meditation, breathing control, and spiritual component. Yet it's very common for reports of studies not to define which type they used. This not only makes it hard to compare results between studies, it also makes it very hard to translate any findings to the bedside when counseling patients. Yoga is broadly defined as a mind-body practice composed of physical postures, breathing techniques, and meditation. And so if researchers say they put yoga to the test, you'd assume all three components would be present. However, some studies use meditation only and call it yoga, with no postures or breathing. Others only examine breathing exercises and call it yoga. Others consider yoga only postures, and still others say they're studying forms of yoga without any of the three components. And so if a study shows no benefit, does that really mean yoga, as commonly practiced, didn't help? And if a study does show benefit, what exactly do you tell patients to do to achieve it? We can take some comfort in the fact that a review entitled Is One Yoga Style Better Than Another attempted to compare the effects of the more than 50 different yoga styles used in hundreds of trials, and they concluded that there was no apparent winner in terms of whether the results turned out positive. So to a certain extent they may be interchangeable. I've talked about the need to have active control to see if there's some benefit to yoga beyond just the exercise component, but such controls may still not deal with confounders such as socialization. Yoga usually involves going to classes, so you can imagine if you were studying the effects of yoga on something like depression. I mean, does breaking routine, getting out and meeting other people have any effect independent of the yoga? Sadly for depression, yoga doesn't even seem to have a benefit compared to doing nothing. Yoga does appear to be helpful with anxiety, but not for people anxious to the extent that they're actually diagnosed with an anxiety disorder, and all the anxiety benefit from yoga appears to just be from the physical activity since there appears to be no benefit compared to other types of exercise. So, unfortunately, yoga does not appear to be effective for mood and anxiety disorders. A review on the effects of yoga on depressive symptoms in people with mental disorders in general, including conditions like PTSD or schizophrenia, found no significant effect compared to things like social support that offer the same kind of attention or to doing nothing, but did find an effect compared to so-called weight list controls. See, unlike in studies of drug effects where a placebo sugar pill is relatively straightforward, selection of a control condition is much more complex for behavioral interventions like yoga. And one common solution is a passive control such as a weight list. Basically, people are randomized to either yoga or onto a weight list where they'll still get yoga but have to wait a while. Now that's better than having no control group at all, since it still controls for the passage of time, meaning whether or not your condition would have just gotten better naturally on its own, but doesn't really control for the placebo effect. If instead you were just told you were entering a study to see if some exercises may help, and then unbeknownst to you, randomized to do yoga versus some sort of sham yoga, then you would have the same kind of expectation either way. But if you know going into it you're going to get yoga now, which may help, or yoga in six months, and you end up in the weight list control, this may spuriously amplify the difference in treatment effect because people assigned to the weight list may expect to not get better without active treatment. For example, study for yoga on urinary incontinence. Women were randomized to six weeks of yoga or a weight list control group. After six weeks, the incontinence frequency decreased by 70% in the yoga therapy, versus only 13% fewer episodes in the control group. But it's possible that the women in the yoga group reported some benefits due to what's called an expectation bias because they expected yoga to be helpful. So based on the body of evidence, one might say there's insufficient good quality evidence to judge whether yoga is useful for women with urinary incontinence. What we'd like to see are studies comparing yoga to time and attention control interventions, some alternative to yoga that entail the same amount of time and attention so people don't even know they're in a control group. Now the question arises, who cares if the benefits from a yoga intervention are due to the placebo effect or expectation bias? A benefit is a benefit. As long as people are getting better, who cares? But it would be nice to know if yoga really helps or not, and here we go. Women with urinary incontinence were randomly assigned to a yoga group or to a rigorous time and attention control group involving nonspecific muscle stretching and strengthening exercises. There are two different types of urinary incontinence, urgency incontinence, defined as an involuntary loss of urine associated with a sudden strong desire to urinate or stress incontinence, where an activity such as sneezing triggers an involuntary leak. Three months of yoga didn't seem to significantly help overall incontinence, but it did seem to help with stress incontinence, decreasing by an average of 61% in the yoga group versus only 35% in controls with no significant changes in urgency incontinence. In our next study we look at how sham acupuncture underscores the necessity of controlling for expectancy effects. Yoga as Therapy When is it helpful? The scientific literature on yoga is limited in scope and quality. I talked about the long list of issues that plague so many of the yoga trials, but let's continue down the list of conditions to get a sense of the best available balance of evidence. For example, yoga as a therapy for irritable bowel syndrome. Evidence from randomized controlled trials found that yoga beat out drugs and was equally effective as moderate intensity walking, so whichever form of exercise you prefer. What about yoga for inflammatory bowel disease? Since stress can be a trigger, might yoga help? In a trial of yoga as an add-on therapy for adolescents with inflammatory bowel disease, it didn't seem to help at all. But in a trial of yoga versus written self-care advice for adults with ulcerative colitis, 12 weeks of yoga induced a stronger increase in quality of life and also reduced disease activity even three months after the study ended. Now, the so-called self-care group was really just handed a couple of general self-care books, so the two treatments, yoga versus self-care, were not matched at all for time intensity, but feeling part of a group or for therapist contact, each of which are likely to have the yoga or more likely to non-specifically improve their quality of life. So yes, yoga might be effective in improving quality of life and ulcerative colitis. However, the benefits may be no different to other group exercise, for example. Indeed, there have been 11 human studies on the influence of moderate exercise programs upon disease activity and chronic inflammatory bowel disease, and all 11 report benefit in terms of reduced disease activity. Using passive controls doesn't account for expectancy effects, attention given to the study subjects and the time spent, the investment that the participants put in. Here's an excellent example of why having more active control groups is so important. This details a series of studies on non-pharmacological interventions for menopausal hot flashes. For example, randomized to eight weeks of acupuncture, eight weeks of sham acupuncture, or nothing, just usual care. Sham acupuncture is when they still stick needles in you, but shallowly and not in traditional acupuncture points. There was also a study of 10 weeks of yoga classes, or the attention control health and wellness education classes, which lasted just as long as the yoga and were done in the same kind of group social setting. Here's what they found. The hot flashes in the usual care group, the passive control, where they didn't do anything special, stayed pretty stable, but the real acupuncture worked way better, but so did the sham acupuncture. So, yoga and acupuncture both worked just as well, but so did the non-yoga and fake acupuncture. There just appeared to be a general placebo effect, such that women in all five intervention groups benefited simply by being in a study. That's why it's always better to have the control groups do something so you can have some confidence at least, some of the effect of your intervention is real. But hey, at least they had control groups. This study, 12-minute daily yoga regimen, reverses osteoporotic bone loss caused quite a stir. We know that when it comes to bone health, it's use it or lose it. Exercise early and exercise often. Physical activities are widely accessible, low-cost and highly modifiable contributor to bone health. Exercise transmits forces through the skeleton, generating signals that are detected by your bone-building cells. This is why the National Osteoporosis Foundation, the International Osteoporosis Foundation, and other agencies recommend weight-bearing exercises for the prevention of osteoporosis. These include high-impact exercises such as jumping, aerobics, and running, as well as lower-impact exercises such as walking and weight training to create these mechanical signals that spark bone growth. Lower-impact activities such as yoga are generally not considered bone-building. That's why the results of this study were so surprising. It was a study of internet-recruited volunteers comparing bone mineral density changes before and after yoga. The researchers devised a 12-minute DVD of 12 yoga poses that they believed would stimulate increased bone density in the spine and both parts of the hip. But in the end, out of the 741 patients recruited at the beginning, only a few dozen actually sent in their bone scans as instructed. So that's only like 5%, right? So they lost 95% of the people that originally started. You can totally imagine how those who got positive results were more likely to send them in, and the others that failed just kind of slunk away. So I don't consider this convincing evidence. Now the authors had the attitude of, hey look, so what do you got to lose? The side effects of yoga are all good, so why not give it a try? Well what you have to lose is the opportunity to do higher-impact exercise that has more decisive evidence of bone benefit. And all the side effects are not necessarily good. There have been vertebral compression fractures associated with yoga. In this series of nine cases from the Mayo Clinic, they describe spinal compression fractures occurring a month to years after initiating yoga-associated spinal flexion exercises. Both scientific and media reports continue to advertise yoga as a bone-protective activity, but there's a need for selectivity in yoga poses in populations that increased fracture risk. And four of the nine patients developed a fracture in a setting of normal or near-normal bone mineral density. So maybe everyone should be careful with these. Yoga-related injuries are not uncommon, resulting in thousands of emergency room visits a year, and approximately 5% of those are coming in with fractures. I'll try to put that injury rate in context comparing yoga to other physical activities next. Even though for certain health conditions we have not reached a point where we can say there's good scientific evidence that yoga is beneficial, many patients do seem to benefit. And isn't that what matters? I mean, even in the studies that show the benefit is mainly a placebo effect, does this really matter? And after all, this editorial asserted yoga therapy has never been shown to have adverse effects, but that's simply not true. About 2,000 yoga-related injuries have been seen in hospital emergency rooms every year from 2001 to 2014. It looks like only one fatalities have been reported in the medical literature, but if you look at the case report, a 16-year-old girl collapsing with a ruptured lung following voluntary mouth-to-mouth yoga breathing exercises with a teenage boy in the hall, that can hardly be characterized as a typical yoga practice. There are tragic, rare cases tied to actual yoga, like this quad rupture in a young woman, or, God, a femoral fracture. The femur is the bone in your thigh, longest, strongest, heaviest bone in the body. Typically, you only see femur fractures with trauma, such as car crashes, but here was just a guy practicing yoga posture when he heard a large cracking sound and felt immense pain because, yikes! Now, two weeks earlier, he had felt pain in his thigh that he just thought was muscle strain, but bone biopsies showed evidence of previous micro fractures, so it sounds like he had been overdoing it, weakening it before the final crack. So, I guess the bottom line is that people should listen to their bodies and not push themselves too far. Now, I talked about the risk of spinal compression fractures, particularly those with weakened bones, osteopenia, or osteoporosis. Poses causing hyperflexion and hyperextension of the spine should probably be avoided. These were the poses tied to injury in a few dozen cases of musculoskeletal injuries described at the Mayo Clinic, but case reports and series of case reports are really just kind of glorified anecdotes. I mean, they don't give you an overall sense of the safety of yoga. If you look at randomized controlled yoga trials, there's actually no significant difference in injury rates between the yoga groups and the control groups that use some other sort of exercise intervention. Now, this may not necessarily translate out into real-world experience, given the short duration of yoga in these clinical trials, as little as a single day, and the fact that they may be more closely supervised with more highly trained teachers. That's why large-scale surveys can be helpful, looking at thousands of people taking yoga classes. Looks like about 30% of yoga class attendees had experienced some type of adverse event, most commonly just something mild, like muscle aches, but some individuals did experience more severe events, which caused them to stop going. Many causes were associated with overexertion and overdoing and starting out in poor physical condition. This systematic review included nine observational studies with 9,000-plus yoga practitioners and 9,000-plus non-yoga practitioners from the U.S., Europe, Asia, and Australia. A considerable proportion of yoga practitioners experienced injuries or other adverse events, however most were mild and transient, and risks were comparable to those of non-yoga practitioners. The risk of yoga-associated injuries was estimated as 1.45 per thousand hours of yoga practice, much lower than in higher-impact sports activities such as soccer. Compared to 1.5 for yoga, runners have like 2.5 injuries per thousand hours. Soccer, 3.75 for tennis, an hour of yoga is more than five times safer than skiing. Here's where yoga falls on the spectrum. Yoga appears much safer, for example, than aerobic funk. On the other hand, yoga practitioners may suffer an increased risk of meniscus injury. The main stabilizing and cushioning cartilage in the knee, yoga was found associated with significantly higher risk of meniscus injury compared with activities such as badminton, jogging, and climbing hills. Some fundamental yoga postures, like the lotus position, can be hard on the knees. Yes, yoga poses can undoubtedly improve the flexibility of the knee, but immoderate joint movement can pose a serious threat. The bottom line is like any other type of physical activity, yoga carries a risk of injury. Exercise is indeed medicine, but like any medicine, it must be prescribed appropriately. Many patients rely on their yoga practice for stress reduction, so it's important to be mindful that being injured is the last thing you need. The higher risk yoga poses appear to include headstands, shoulder stands, lotus and half-lotus, forward bends, backward bends, and handstands. And so beginners should be aware, with particular tension paid to the spine, as this is where the highest numbers of injuries occur. Hot yoga deserves special mention. The extreme heat and intensity of bichrom yoga may make it inappropriate for older adults and people with medical conditions, but there are case reports of sudden cardiac arrest, even in a healthy 35-year-old. Pregnancy is an especially vulnerable time for heat exposure. With the increased risk of spinal defects and possibly other birth defects among fetuses exposed to excessive heat, pregnant women should avoid practicing hot yoga during pregnancy. Maternal hyperthermia, whether from a sauna or electric blankets, had a nearly two-fold increased risk of spinal and brain malformations. For example, pregnant women who use hot tubs increase the risk of bearing babies with their intestines outside their bodies or being born without a brain. As any other physical or mental practice, yoga should be practiced carefully under the guidance of a qualified instructor. Beginners should avoid extreme practices, such as headstand, lotus position, forceful breathing. Individuals with medical preconditions should work with their physician and yoga teacher to appropriately adapt postures. For example, patients with glaucoma should avoid upside-down positions, and patients with compromised bones should avoid forceful yoga practices. And practices like voluntary vomiting should perhaps be avoided completely. What? It's evidently common practice in traditional yoga. We may be able to share it on social media to help inspire others. If you'd like to see any graphs, charts, graphics, images or studies mentioned here, go to the Nutrition Facts Podcast landing page where you'll find all the detailed information you need, plus links to all the sources we cite for each of these topics. My last two books were How to Survive a Pandemic and My How Not to Diet Cookbook. Get ready this year for the launch of How Not to Age, and of course all the proceeds for the sales of all my books goes directly to charity. NutritionFacts.org is a non-profit science-based public service where you can sign up for free daily updates on the latest new nutrition research with bite-sized videos and articles uploaded nearly every day. Everything on the website is free. There are no ads, no corporate sponsorships, no kickbacks. It's strictly non-commercial, not selling anything. I just put it up as a public service as a labor of love as a tribute to my grandmother, whose own life was saved with evidence-based nutrition.