How does yoga reduce stress? A systematic review of mechanisms of change and guide to future Inquiry
Yoga is morphing into something much greater than a mere physical fitness regime. It is now being used to administer remedies in clinical offices the world wide. It’s efficacy for stress reduction is intuitively understood but remains poorly studied and understood in the western sense. The authors of this study searched databases conducting systematic reviews of other studies conducted targeted toward measuring stress management/reduction outcomes via the practice of yoga. The authors noted positive effects such as self-compassion and salivary control helped to regulate stress. However, given the numerous studies only seven mechanisms were identified that play a recognizable role in yoga and stress reduction.
This study was conducted by Kristen E. Riley and Crystal L. Park both working in the Department of Psychology at University of Connecticut. In this study from Health Psychology Review, 2015 the authors posit the mechanisms in which yoga impacts driving direct health benefits such as positivity, self-compassion, inhibition of the posterior hypothalamus and salivary cortisol levels. The researchers conducted research on existing studies to flesh out the ways in which (if at all) yoga reduces stress. Differentiating between psychological benefits versus more concrete measures such as bio-markers called “mechanisms.” The authors give a thorough explanation/definitions of stress, does yoga reduce the same, proposed mechanisms both biological and psychological, methodology, search criteria and finally synthesis and results.
This is an effort to create a snapshot of where research stands in terms of the efficacy of yoga and stress. As yoga continues to penetrate deep into the western mind empirical evidence is crucial if yoga is to gain respect as part of the healthcare system. Stress is a true killer, thus a sustained effort linking stress reduction to yoga is important as I believe the price point for a yoga intervention vis-á-vis our current HMO system is the best course of action.
The authors found 926 abstracts and filtered these down to 5 for systematic review. Weighed 4 for biomarkers and 3 for psychological mechanisms. It would have been best to have studied 6 total for an even comparison. The psychological mechanisms weight more toward the social sciences versus hard sciences making these factors more subjective. The studies used Hatha yoga as the controlling factor. This is a methodological flaw as Hatha could be as strenuous as a Bikram style yoga class or a gentle flow. Effort was made to compare “expert” yogis to new students without defining each, nor the complexity of asana for each. Results could be incorrect based upon whether inversions were offered to experts, where new students lack to skill to invert for example.
Biomarkers were used to success in measuring the HPA axis, baroreflex sensitivity and vagal nerve stimulation decrease. Specifically HPA axis showed positive endothelial function and release of nitric oxide. Endocrine response showed stress reduction measured by plasma cortisol levels and reduction in inflammation. Even short term yoga intervention demonstrated “increased activity of antiviral interferon regulatory factor, both associated with chronic stress” (382). One criticism I have is they used a study from 1983 using the hypothalamus as the mechanism. This study is to old in my view to be credible, supporting the idea that fresh research is sorely needed.
In conclusion, much more rigorous research needs to be done. Accurate control groups need to be setup to differentiate the styles of yoga and the level of practitioners. Yoga and stress reduction could have a tremendous impact on society, but the research needs to be methodized to include the fuller system of yoga to include the entire eight yogic disciplines of aṣtanga yoga. Siloing off different components of yoga, i.e. meditation, āsana or prāṇāyāma is too narrow in my view.
Kristen E. Riley & Crystal L. Park. How does yoga reduce stress? A systematic review of the mechanisms of change and guide to future inquiry. Health and Psychology Review. 15 April 2015.