The Science of Yoga

inspected the disks for signs of damage. The results, the team wrote, showed that the yoga teachers had “significantly less” degenerative disease than the control group.
    Why? The physicians suggested that spinal flexing may have caused more nutrients to diffuse into the disks. Another possibility, they wrote, was that the repeated tension and compression of the disks stimulated the production of growth factors that limited aging.
    The frontiers of biomedical science turn out to hold many clues to prospective health benefits. The new understandings reveal potential—if unproven—rewards for practitioners even if the word “yoga” never appears in the text or title of a scientific paper.
    One surprise centers on the vagus, often portrayed as the most important nerve in the body. It travels from the brainstem to the torso, where it radiates out tothe lungs, heart, stomach, liver, spleen, colon, and other parts of the abdomen. The word vagus shares etymological roots with “vagrant” and “vagabond,” denoting how it wanders through the body.
    The nerve’s action is central to the regulation and slowing of the human heartbeat, and thus has played important roles in ostensible miracles going back to the days of the Punjab yogi. But the new research focuses on what turns out to be an even more fundamental talent of the nerve—the regulation of the immune system, in theory offering protection against a number of serious illnesses.
    The body’s immune response is typically portrayed as white blood cells battling foreign invaders, and the immune and nervous systems as distinct entities—like oil and water, never mixing. The itinerant nerve would thus seem to have nothing whatsoever to do with the body’s defense mechanisms.
    Kevin J. Tracey found otherwise. In 2002, the immunologist at the North Shore University Hospital on Long Island, New York, reported that the vagus wields remarkable control over the body’s immune system, playing major roles, for instance, in fighting inflammation.
    That may sound unimportant. But a number of deadly conditions arise from the body’s overreaction to infection or its threat. For instance, the whole body can swing into an inflammatory state known as sepsis, a quiet killer that in the United States takes more than two hundred thousand lives each year. Other disorders include lupus (an autoimmune disease), pancreatitis (a chronic inflammation of the pancreas), and rheumatoid arthritis (a chronic inflammation of the joints). Scientists are working hard on anti-inflammatory therapies.
    Tracey initially focused on drugs meant to excite the vagus. But the more he learned of yoga and other Eastern disciplines, the more interested he became in their potential as natural agents to fight inflammation and its debilitating effects. In 2006, he discussed the topic at a conference held under the auspices of the Dalai Lama, the Tibetan spiritual leader who has long shown an interest in Western science.
    Tracey’s ideas won support in 2011 when Indian scientists under the leadership of Shirley Telles—one of yoga’s most prolific investigators—reported that doing intensive practice for a week can ease trauma from rheumatoid arthritis, the painful disorder of the joints. It afflicts millions of people. The study looked at sixty-four patients, ranging in age from twenty to seventy. Theyoga included flexing poses and slow breathing, which stimulates the vagus. Measurements at the beginning and end of the week showed drops in rheumatoid factor—an indicator in the bloodstream of the disease—as well as improvements in the ability of practitioners to get out of bed, dress, walk, eat, and grip objects.
    Investigators of the invisible are finding even deeper allures. They include an ultimate expression of good health—longevity.
    Few topics in yoga have produced more fog. The mythology goes back at least as far as Marco Polo, who first visited India around 1288 and reported that yogis could live for as long as two centuries. Today, yogis and yoga teachers routinely hail the practice as greatly prolonging life—though no study that I know of has examined that claim. What makes headlines are anecdotes. For instance, many authors point to the longevity of Krishnamacharya, who became a centenarian. So too his student Indra Devi, author of Forever Young , drew attention by living to be one hundred and two. Few yoga enthusiasts mention that pudgy Yogananda died of a heart attack before he