The Healing Power of Yoga Controversy Adapted from the Afterword to "The Science of Yoga," paperback edition. When "The Science of Yoga" was published a year ago, it stirred more controversy than anything I've ever written as a science journalist. Before it came out, Bobby Clennell, my talented illustrator and a senior Iyengar teacher with a global following, told me that the book would start a conversation. The reality was more like a riot. The outcry began when an excerpt ran in The Times Magazine in January 2012 under the headline "How Yoga Can Wreck Your Body." A furious yogi shot back: "You are a wreck." The excerpt was illustrated with photos of the Broadway cast of "Godspell" twisted into exaggerated poses. The postures were meant to be funny. But lots of yogis took offense. As a Chicago-based columnist remarked, the article provoked "more coverage, umbrage and yuppie outrage than the wars in Afghanistan and Iraq combined." Yoga for many people is a sacred refuge. But as I learned of the dangers, I felt an obligation to help people disentangle the good aspects of the practice from the bad. After all, yoga too often is sold as completely safe - "as safe as mother's milk," as a prominent guru once declared. Most of the hundreds of e-mails and letters I received - from yoga teachers and celebrities, doctors and therapists, yoga schools and studio owners - since the excerpt's appearance and the book's publication were written in gratitude and support. Many described injuries. A teacher of nearly two decades wrote with elegant simplicity: "Thank you." Critics accused me of sensationalism. But the flurry of letters argued otherwise. People described damage like strokes, spinal stenosis, nerve injury, disk rupture and dead spinal tissue. "I am currently recovering from cervical fusion and will need a lifetime of physical therapy," a former studio owner wrote. One of the saddest and most thoughtful letters came from an elderly man who studied with Iyengar in India for 16 years. His list of personal injuries included torn ligaments, damaged vertebrae, slipped disks, deformed knees and ruptured blood vessels in his brain. "All that you wrote," he said, "I can confirm in my own life." I also learned that a number of accomplished yogis had written whole books about how to avoid yoga injuries. The books received scant attention but demonstrated the depth of concern. Kevin Khalili, a doctor in Santa Barbara, Calif., wrote "X-Posed," published in 2011. Jean-Paul Bouteloup, a yoga teacher in Paris, wrote "Yoga Sans Dégâts" ("Yoga Without Damage"), published in 2006. And as early as 1980, a student of B.K.S. Iyengar - one of modern yoga's founders - published "Attention, le Yoga Peut Être Dangereux Pour Vous!" ("Warning - Yoga Can Be Dangerous for You!"), written with a doctor and issued by the Iyengar institute in Paris. Federal investigators turned out to have gathered many reports that supported the anecdotal evidence. They had selected roughly 100 emergency rooms whose locations and demographics mirrored the nation's 5,300 hospitals with emergency services, and the monitoring of that network led to their statistical portraits. The sample of hospital emergency rooms in 2002 showed a spike in yoga injuries to 46. By 2011, the rate had more than doubled, to 100 cases. The increase seemed to reflect yoga's growing popularity. The chart below gives the national estimates of injury: Over the past decade, the annual federal estimates add up to more than 20,000 injuries. By definition, that figure excludes yogis who sought help from clinics, family doctors, yoga therapists, urgent-care centers and other healers - or who sought no help at all. So the big picture is unknown. Yoga's defenders would argue that if 20 million people in the United States have practiced yoga in the past decade, just 0.1 percent - or 1 person in 1,000 - went to emergency rooms. They see injury rates for activities like weight lifting and even golf as higher. Fair enough. All exercise involves some degree of risk, and yoga is no different. The trouble with rate comparisons is that they focus exclusively on the quantity of injuries and ignore their quality, or severity. No study that I know of has compared the injuries of sports and yoga in terms of gravity. Perhaps they are similar. After all, most yoga injuries tend to be minor - strains and sprains. But the hospital reports demonstrate that yoga can also result in fracture, seizure, dislocation of joints, heart failure, spinal displacement, deep-vein thrombosis, vertigo, nerve injury and brain damage. In time, research will likely clarify the differences. It may turn out that yoga, despite a low rate of injury, is unusually dangerous. Much skepticism - even anger - was directed at the claim I made in both the article and the book that yoga can lead to strokes or brain damage. The evidence lies not just in the studies I cited but medical reviews in 1989, 1994 and 2001 that described yoga strokes, as well as recent federal reporting about a new case. Unfortunately, no scientist has published data on how often yogis suffer strokes and compared the rate with other sources of brain damage. I think it's fair to assume that the risks are low - but how low is an open question. So too, readers doubted that yoga could kill. Yet many yogis in apparent good health die suddenly - at times during hard training. Jeff Goodman, 58, died following a class, which was part of an advanced training course in Houston in April 2012. Tiffany Neff, 25, died a month earlier in Moreland Hills, Ohio. Jules Paxton, 45, died in New York City in 2011, as did Bill Jackson, 55, in Naples, Fla. Eric Berliner, 58, died in Chicago in 2010 during a master class. Abbey Duncan, 27, a yoga teacher, died that same year in Minneapolis. In Los Angeles in 2004, Sita White, 43, a British heiress and a favorite of gossip columnists, collapsed and died in a yoga class. The question is why. Medical authorities in some cases cite natural causes. But does that rule out yoga? Jeff Goodman, the Houston yogi, was said to have died of a brain aneurysm - the thinning and ballooning of an arterial wall. Burst aneurysms have been linked to exercises like push-ups and weight lifting, which produce spikes in blood pressure as the breath is held and the abdominal muscles are contracted. Yogis do that all the time. Yoga authorities are right in saying that known injuries have resulted in no reported deaths. But that speaks to the limits of data collection and reporting in biomedicine rather than a demonstrable absence of fatalities among millions of yoga practitioners. It's a state of ignorance versus one of knowledge. My exploration of this world has prompted me to alert yogis whenever possible to what are probably very low risks that can have extremely severe consequences. During public talks, I often read aloud the letters I've received that detail yoga strokes. Below, I quote from one such letter - a male practitioner with considerable experience, whose doctors linked his stroke to the plow pose. "I remember thinking as I was doing the exercise that it felt like an unhealthy amount of pressure on my neck," he wrote. After the yoga series, I had a crushing headache, which was a rarity for me. The next morning, I noticed my left eyelid was drooping. At first, I thought it was possibly due to a sinus infection, because I had a cold at the time. But later I noticed that my left pupil was constricted. It took weeks of trips to different doctors before I was diagnosed. His doctors told him that the odds of surviving the brain damage were one in 10,000. The man had surgery to correct his drooping eyelid as well as four years of drugs, therapy and brain scans. "It's good," he wrote, "that your article presents a warning." Yet, for all the bad news about yoga, I still see the rewards as outweighing the risks. A century and a half of science shows the benefits to be many - and the serious dangers to be few and comparatively rare. Readers of the magazine article had no way of knowing that the book detailed yoga's advantages for health and healing, sex and longevity, moods and creativity. And most had no idea that I'm a yoga enthusiast, not a basher. But yoga has to be done intelligently. The continuing debate over "The Science of Yoga" has sparked widespread discussion of how to improve safety. Over and over, I've heard of classes discussing the pros and the cons of different styles and poses. "How NOT to Wreck Your Body," read the ad for a Boston class. We will examine the 'most dangerous' yoga postures and offer safe methods of practice. Many people have told me of old routines updated, of new precautions taken, of fresh emphasis on fitting the pose to the person (and the person's gender) rather than twisting bodies into idealized postures. A number of yoga schools now use my book in teacher training. "Thank you for opening up a door," wrote a longtime studio owner. The new candor, she added, promised to usher in "improved safety for students - and a positive yoga experience."