I have been standing on my head, off and on, for about 35 years now, as well as sitting cross-legged breathing through one nostril at a time, and — my favorite — lying flat on my back, utterly relaxed, in the so-called “corpse pose.”I am, in other words, one of the 15 million Americans who, according to a Harris Interactive Service Poll done in 2003 for Yoga Journal, have fallen in love with this ancient Indian practice that’s part meditation, part exercise. To the cognoscenti — and our numbers grew by nearly 29 percent between 2002 and 2003 — yoga is a pleasant practice that seems to enhance physical and emotional strength, flexibility and balance. But does it?
Well, to the extent that yoga overlaps with what the so-called “relaxation response,” it’s no leap at all to conclude that yoga is good for you. The “relaxation response,” a term coined years ago by Dr. Herbert Benson, president of the Mind/Body Medical Institute in Boston, consists basically of quieting the mind and body through prayer, contemplation or focusing on something simple, like breathing.
The relaxation response has been shown to lower blood pressure, heart rate and respiration; to reduce anxiety, anger, hostility and mild-to-moderate depression; to help alleviate insomnia, premenstrual syndrome, hot flashes and infertility; and to relieve some types of pain, like tension headaches.
But for yoga itself, there’s not much scientific evidence that the practice confers its own specific health benefits — though that doesn’t seem to dampen anyone’s enthusiasm, including my own.
“There is not enough really good research to draw strong conclusions about anything about yoga,” said health psychologist and yoga teacher Roger Cole of Synchrony Applied Health Sciences, a health promotion consulting firm in Del Mar, Calif.
Take standing on your head. There is some data suggesting that inversion may slow heart rate and make people secrete less of a stress hormone, norepinephrine. “The question,” said Cole, “is whether that amounts to clinical benefits.”
Some yoga teachers claim that standing on your head increases blood flow to the brain, a supposedly good thing. That’s nonsense, said Dr. Timothy McCall, a slim, Somerville physician and yogi who writes a health column for Yoga Journal. “Blood flow to the brain is tightly regulated,” he said, so going upside down probably doesn’t bathe the brain in extra blood. And standing on your head could worsen glaucoma (increased pressure within the eye) and or problems with the retina. That said, McCall is still convinced that headstands “have a profound effect on slowing the body down.”
McCall, who, perhaps more than anyone else, has tried to assess the science of yoga, has visited research institutes in India, where most of the yoga studies are being done.
Though some of the research — both in India and the West — is methodologically flawed, yoga has more than 50 documented effects, including greater strength, increased flexibility, better balance, better cholesterol levels and better mood.Of five studies on asthma since 1985, three showed statistically significant benefits. One 1998 study on carpal tunnel syndrome (pain caused by pressure on a nerve in the wrist) found yoga could reduce some symptoms and improve grip strength. A couple of small studies found that yoga can lead to both subjective and objective improvements in COPD, or chronic obstructive pulmonary disease, a disease in which the airways and air sacs in the lungs lose their elasticity, making it difficult for air to flow in and out.
Another small study found that the slow, diaphragmatic breathing of yoga helps increase oxygenation in some patients with congestive heart failure. Several studies show yoga helps improve symptoms of coronary artery disease, though the patients also made other changes — like switching to low-fat diets. One study of severe depression found that the deep breathing (pranayama) of yoga, electric shock therapy and drugs all improved scores somewhat on a standard depression test.
At Boston’s Brigham and Women’s Hospital, senior neuroscientist Sat Bir Singh Khalsa is studying yoga as a treatment for insomnia. At the University of Texas MD Anderson Cancer Center in Houston, Dr.Lorenzo Cohen, director of the integrative medicine program, hasfinished a 7-week study of 39 men and women with lymphoma that waspublished in April. Cohen randomized patients to receive instruction in Tibetan yoga or no special intervention. Those who practised yoga slept better than those who didn’t, though there were no differences in other measures such as anxiety, depression or fatigue.
Researchers at the UCLA Jonsson Cancer Center are about to start a study of yoga to combat fatigue in women with breast cancer. Put bluntly, yoga may indeed have more health benefits than have been documented so far. But the skimpiness of solid data so far means: Buyer Beware. If you’re in a class and the teacher makes absurd claims — like a certain pose will make your spleen happy — smile serenely and think of the claim as a metaphor.
And choose your teacher with care. Unlike hairdressers and manicurists, yoga teachers are not licensed. Anational organization called Yoga Alliance (www.yogaalliance.org) lists teachers who have completed various levels of training, but it provides no real evidence of competence. Some methods of yoga, like the Iyengar system, do have a rigorous, multi-tiered system of certification, says Patricia Walden, director of the BKS Iyengar Yogamala of Cambridge. But it’s still a crapshoot. So good luck. And, as they say in Sanskrit when one person puts her palms together and offers a humble greeting to another, Namaste.