The Science of Yoga

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 was sixty.
    Despite the wishful thinking, a recent discovery suggests that yoga can indeed slow the biological clock. The finding centers on a long-standing riddle—why cells age, die, or in some cases defy the natural order of things to remain young. The answer involves the microscopic whorls of DNA that lie at the tips of the chromosomes, the central repositories of genetic information in the cells. Scientists have found that these DNA tips, known as telomeres, get shorter each time a cell divides and thus serve as a kind of internal clock that determines the cell’s allotted time in life. They have also discovered the secrets of telomere growth and youthfulness. The finding was considered so important that it won the 2009 Nobel Prize in Physiology or Medicine. To scientists, the story of the telomere suggested a more accurate way of measuring biological age than simply marking the passage of the years.
    As often happens in science, the discovery brought into sharp focus yet another question—why do the telomeres of some individuals hold up much better than others? In some