Updated: Jan 8, 2021
Over the last few decades, interest in the science of yoga has increased both in the lay and scientific communities. The number of studies on yoga has surged in the last 20 years with more scientists focusing not solely on the stress-reducing properties of yoga, but also on its numerous other physiological effects from inflammation and free radical cell damage to glucose metabolism. As a scientist myself, it’s been gratifying to see the change in mindsets among scientists that I believe this reflects. While once believed by many to be a practice of mysticism with no true scientific merit, now a broader audience is accepting yoga as a legitimate lifestyle intervention as a result of rigorous scientific studies documenting its effects.
Most of our research on yoga has focused on heart disease risk factors but our early work also investigated the effects of hot yoga on metabolic health. Those studies showed a significant reduction in the blood glucose response to a glucose tolerance test after 8 weeks of hot yoga in obese adults at risk for diabetes. Our studies have also shown improvements in arterial dilation (this is predictive of heart disease and cardiac events) in adults over the age of 40 at increased risk for heart disease and a reduction in arterial stiffness (the rigidity of the vessel which predisposes the inner lining for plaque formation) in overweight adults after 8-week Bikram yoga interventions.
While these findings were promising, in addition to providing a clearer understanding of yoga’s benefits, these studies also generated more questions. For instance, as yoga is the confluence of postures, breathing, focus, and sometimes meditation, which of these elements is causing these health benefits to occur? Can people realize the same benefits from doing pranayama (breathing practices) as they would from consistently practicing postures and breathing combined? When investigating a lifestyle intervention like yoga that is composed of many constituents, the next natural step in the scientific process is to tease out which aspect is causing most of the benefits.
To this end, studies have focused on either yoga postures alone or combined with breathing and doing side-by-side comparisons of the results. A recent study published in Frontiers in Physiology investigated whether yogic breathing enhanced the effects of yoga postures or stretching on vascular health. They looked at arterial stiffness and dilation capacity, both of which are associated with the future risk of heart disease, and compared 3 interventions: stretching or yoga (this was a sort of control condition); yoga postures with ujjayi breathing cues; or stretching combined with ujjayi breathing. They recruited postmenopausal women because declines in estrogen during this phase of life cause downstream effects on the blood vessels making them more prone to plaque buildup and increasing the risk of heart disease. They also took blood samples and looked at antioxidant (the body’s ability to neutralize potentially harmful free radicals) in addition to other markers of free radical damage.
Both the yoga posture and stretching interventions (with ujjayi) reduced arterial stiffness after 12 weeks of 2 classes per week while stretching or yoga alone had no effect. Blood vessel dilation capacity, however, improved in all 3 groups (yoga + breathing, stretching + breathing, or yoga or stretching alone). All 3 interventions also improved antioxidant capacity, but only the interventions with pranayama included reduced free radical cell damage. This is a key finding which could lend insight into yoga's potential antiaging effects. While this study had limitations one of which was a high dropout rate (34% of study participants quit before the end of the 12-week intervention), it was a timely first step in exploring this burgeoning question of which element of yoga is the key mechanism by which it exerts its health benefits.
Two limitations not mentioned in the manuscript that I believe obscure the interpretation of their findings was that both that yoga was compared to stretching and that both groups practiced yogic breathing during the classes. Thus, since both groups practiced pranayama, they weren’t truly able to isolate the contribution of yogic breathing to their outcomes. Their control group had did either stretching or yoga, which also limits the interpretation of their results. If a yoga posture intervention with or without pranayama were compared side-by-side, this could have provided a clearer picture as to whether yogic breathing made a difference. Limitations are ubiquitous in any research study and all studies including my own have some flaws or perceived shortcomings. I simply point this out to help readers to properly interpret the results from this paper without making conclusions beyond the scope of the study design. As my own interest in the specific contribution of yogic breathing to yoga's health benefits continues to grow, I’m considering ways to investigate this topic. If you’re a yoga teacher and have any thoughts on this, I’d love to hear from you.
Since breathing is so integral to the practice, it would probably be better to compare a traditional posture and yogic breathing class to pranayama alone instead of having one study group solely execute yoga postures without any breathing or additional cues. I think the latter could lead to people holding their breath or doing the Valsalva maneuver (squeezing the throat closed while attempting to forcefully exhale) while straining to hold warrior for instance and this could lead to negative consequences like an excessive increase in blood pressure and potential arterial wall damage. I also wonder how to address this research question without compromising the integrity of the practice. If people are simply doing yoga poses without the additional elements, are they really doing yoga and can that truly be considered a yoga intervention study?
The article linked above is freely available to the public (with no download fees).