Why Yoga Works

With the ever-growing amount of scientific studies conducted in the field of yoga research, it’s no surprise that we’re starting to get answers to the question: Why, exactly, does yoga work? Research has shown that yoga improves symptoms of a variety of conditions, providing relief from depression and anxiety, diabetes, chronic pain, and even epilepsy. Recently, the National Institutes of Health awarded several large grants to the study of yoga.

One such grant, given to Lorenzo Cohen, PhD, director of the Integrative Medicine Program at the University of Texas MD Anderson Cancer Center, explores the impact of yoga on the health of women with breast cancer. Another grant, awarded to Kripalu Research Director Sat Bir S. Khalsa, PhD, assistant professor in the Division of Sleep Medicine at Brigham and Women’s Hospital, supports a study to investigate whether Kripalu Yoga prevents or diminishes high school students’ use of illicit substances.

This has been an exciting time for yoga research, as more studies emerge that continue to shed light on how yoga is effective in alleviating many mental and physical health problems.

Researcher Chris Streeter, PhD, associate professor of psychiatry and neurology at Boston University School of Medicine, recently released an article, “Effects of Yoga on the Autonomic Nervous System, Gamma-aminobutyric-acid, and Allostasis in Epilepsy, Depression, and Post-traumatic stress disorder,” detailing what are believed to be the underlying physiological mechanisms, or, simply put, yoga’s impact on the body and brain.

Chris and her team hypothesize that yoga helps regulate the nervous system by increasing what’s called vagal tone, or the body’s ability to successfully respond to stress. Improvements in vagal tone have been shown to correlate with reductions in allostatic load (the amount of stress we accumulate over time). The researchers believe that the reason yoga helps increase resilience and well-being is because of its positive impact on vagal tone.

So what’s the vagal tone all about? It’s directly related to the state of the vagus nerve, which is our largest cranial nerve. It’s also known as the “wandering nerve” because of its mobility through the body. The vagal tone starts at the base of the skull and travels throughout the body, touching the respiratory, digestive, and nervous systems. Often thought of as our “air-traffic controller,” the vagus nerve helps regulate all our major bodily functions. Breathing, heart rate, digestion, and even how we take in, process, and make meaning of our experiences are all directly related to the vagus nerve.

It’s easy to see, then, why the vagus nerve is critical to optimal physiological functioning, as well as a significant marker of resilience. People with healthy vagus nerve functioning are considered to have “high vagal tone,” meaning their bodies and brains are more resilient under stress. They have an easier time moving from an excited state to a relaxed one. Someone with high vagal tone, for example, would recover faster from a fight with a spouse than someone with low vagal tone. Not surprisingly, these individuals tend to be healthier and more resilient.

People with low vagal tone, on the other hand, are more sensitive to stress and disease. They tend to have challenges such as weak digestion, increased heart rate, and difficulty managing emotions. Interestingly, low vagal tone is correlated with such health conditions as depression, anxiety, chronic pain, and epilepsy—the very same conditions that show significant improvement with yoga practice. Researchers hypothesize that vagal stimulation through yoga may improve these conditions.

How else does this relate to yoga? A growing amount of research shows that yogic practices such as pranayama, or breathing techniques, significantly increase vagal tone. “Resistance breathing,” such as Ujjayi (ocean-sounding breath), increase parasympathetic activity (the relaxation response) as well as heart rate variability—another marker of resilience.

As scientists begin to unravel how yoga works, yoga teachers, in turn, will continue to increase their understanding of which practices produce what responses, and why. Studies such as the ones above continue to produce fascinating insight into the science of yoga, helping researchers such as our Kripalu-affiliated scientists fine-tune their measures as they explore yoga’s impact on various health conditions.

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