Stress Yoga and Cortisol
Many studies have documented that yoga can have an array of psychological, physiological and physical health benefits for healthy individuals as well as those coping with disease (e.g., Morgan, Irwin, Chung and Wang, 2014; Sengupta, 2012). However, the mechanism through which these yoga-induced health benefits occur is less clear. One possible pathway linking yoga with positive health outcomes is through stress reduction, or reducing one’s reactivity during stressful circumstances. This is a plausible mechanism, given that there is a robust connection between experiencing stressors and adverse health outcomes (e.g., McEwen, 1998; Sapolsky, 2004). This association between stressors and health could be due in part to stress-induced changes in important physiological systems, including the stress hormone cortisol. If yoga enables people to better cope with the stressors they face, this could lead to less stress-induced physiological activation (e.g., less of an increase in cortisol), which in turn could impact health.
The stress hormone cortisol may be a prime candidate as a physiological mediator of the yoga-health association, based on evidence that certain types of stressors can increase cortisol, and the regulation of this hormone in turn can impact health. The prototypical context where cortisol can be activated is in response to a physical threat, such as when survival or safety is threatened; cortisol can mobilize energy resources to effectively respond to the short-term metabolic demands of the threat (e.g., fighting or fleeing). There is increasing evidence that cortisol can also be activated in response to social threat, such as situations in which one feels rejected or evaluated by others (e.g., Dickerson & Kemeny, 2004). For example, in our studies in which participants are randomly assigned to deliver a speech along in a room (non-social context) or in front of an evaluative audience (social context), only the social evaluative stressor elicits a cortisol response (e.g., Dickerson, Mycek & Zaldivar, 2008; Woody, Hooker, Zoccola, & Dickerson, 2018). These and other studies have demonstrated that cortisol is very attuned to the social context and is triggered when we feel evaluated, rejected or devalued; given that we may encounter many such social stressors in daily life, we may be exposed to many situations that could elicit cortisol reactivity. If the cortisol response is frequently activated or fails to shut off after the end of a stressor, this could lead to over-exposure to cortisol and dysregulation in this system. Specifically, cortisol dysregulation has been associated with suppression of aspects of the immune system, damage to neurons (e.g., in the hippocampus), and the development and exacerbation of different disease states. Therefore, it is important to try to identify ways in which we might be able to “quiet” or better regulate the cortisol response, and therefore mitigate these negative effects on health.
Yoga may be one method to regulate the cortisol response – yoga could shift cortisol trajectories to stressors, which in turn could in turn lead to improvements health outcomes. This could happen through stress reactivity – yoga could alter the way we respond psychologically and physiologically to stressors (e.g., less cortisol reactivity). The reduction of cortisol reactivity to stressors through yoga could confer health benefits.
There is growing support for the premise that yoga could reduce cortisol reactivity to stressors. The basic methodology of these studies is that participants are randomly assigned to participate in a yoga intervention or a control condition, and then subsequently go through a stressor in the laboratory (e.g., difficult cognitive task, delivering a speech). Cortisol is assessed before and after the stressor. This design allows a test of whether yoga leads to differences in stress reactivity.
Benvenutti et al. (2017) had 24 participants complete a yoga session (30 minutes of video-instructed Hatha yoga) or a control session (watching TV) on different days. Following both the yoga and control sessions, the participants then completed a standardized laboratory stressor and cortisol reactivity was assessed. Another study (Gothe, Keswani & McAuley, 2016) recruited 118 sedentary adults, who were randomly assigned to participate in either an 8-week yoga intervention (3 hatha yoga classes per week) or a control group (3 classes per week of stretching exercises). They then completed a challenging cognitive task. Both studies found that the yoga condition had less cortisol reactivity to a laboratory stressor than the control condition; in other words, a single yoga session or regular yoga practice reduced cortisol responses to a subsequent stressor.
Another study assessed cortisol reactivity to a laboratory stressor (speech and math task), then randomly assigned 52 female participants to a yoga intervention (2 Bikram yoga classes per week for 8 weeks) or a waitlist control; then stress reactivity was re-assessed (Hopkins et al., 2016). There was not a significant effect overall between the yoga and control groups in terms of cortisol reactivity following the intervention; however, those who showed exaggerated cortisol reactivity initially showed greater reductions in cortisol when assigned to the yoga condition. In other words, yoga reduced cortisol reactivity among the initial “high reactors.”
Taken together, these methodologically rigorous studies suggest that yoga may lead to reduced cortisol reactivity to stressors. However, more research should be done to replicate and extend these findings, as important questions remain. For example, the psychological mechanism of these effects has yet to be delineated. After yoga, do individuals appraise the stressor differently, or respond with different emotions – and does this in turn affect cortisol reactivity? Understanding how yoga may lead to cognitive or affective shifts which in turn shape physiology will be an important next step. Additionally, the “critical ingredient” of the yoga practice that translates into reductions in physiological reactivity will need to be unpacked. These studies examined Bikram and Hatha yoga – but the intensity, frequency and style of yoga that most effectively leads to substantive stress reductions has yet to be empirically tested. Practices of different intensities, duration, and orientation may have different physiological consequences. Further, other research has found similar results with mindfulness meditation – for example, cortisol reactivity has been reduced (e.g., Creswell, Pacilio, Lindsay, & Brown, 2014) or better regulated (Manigault, Woody, Zoccola, & Dickerson, 2018) among those randomly assigned to a mindfulness meditation intervention or who are high on trait mindfulness. Therefore, studies that compare meditation, yoga, and other mind-body interventions (e.g., tai chi) could elucidate common and distinct pathways through which these two practices could influence physiological reactivity and health.
In sum, there is consistent evidence that yoga may serve as a stress-buffer – leading to better regulation of cortisol reactivity to stressors. This provides empirical evidence for a phenomenon many yogis have intrinsically understood – what happens “on the mat” can have an effect on how one responds to “off the mat” stressful experiences. Yoga has the potential to improve health outcomes via the regulation of stress-responsive systems; the next phase of research is needed to usher in a greater understanding of yoga’s benefits and the mechanisms through which they may occur.
RERFERENCES CITED
Benvenutti, M. J., Alves, E. D., Michael, S., Ding, D., Stamatakis, M., & Edwards, K. M. (2017). A single session of hatha yoga improves stress reactivity and recover after an acute psychological stress task: A counterbalanced, randomized crossover trial in healthy individuals. Complementary Therapies in Medicine, 35, 120-126.
Creswell, J. D., Pacilio, L. E., Lindsay, E. K., & Brown, K. W. (2014). Brief mindfulness training alters psychological and neuroendocrine responses to social evaluative stress. Psychoneuroendocrinology, 44, 1-12.
Dickerson, S. S., & Kemeny, M. E. (2004). Acute stressors and cortisol responses: A theoretical integration and synthesis of laboratory research. Psychological Bulletin, 130(3), 355-391.
Dickerson, S. S., Mycek, P. J., & Zaldivar, F. (2008). Social evaluation – but not mere social presence – elicits cortisol responses to a laboratory stressor task. Health Psychology, 27(1), 116-121.
Gothe, N. P., Keswani, R. K., & McAuley, E. (2016). Yoga practice improves executive function by attenuating stress levels. Biological Psychology, 121, 109-116.
Hopkins, L. B., Medina, J. L., Baird, S. O., Rosenfield, D., Powers, M. B., & Smits, J. A. J. (2016). Heated hatha yoga to target cortisol reactivity to stress and affective eating in women at risk for obesity-related illnesses: A randomized controlled trial. Journal of Consulting and Clinical Psychology, 84(6), 558-564.
Manigault, A. W., Woody, A., Zoccola, P. M., & Dickerson, S. S. (2018). Education is associated with the magnitude of cortisol responses to psychosocial stress in college students. International Journal of Behavioral Medicine, 1-8.
McEwen, B. S. (1998). Stress, adaptation, and disease: Allostasis and allostatic load. Annals of the New York Academy of Sciences, 840, 33-44.
Morgan, N., Irwin, M. R., Chung, M., & Wang, C. (2014). The effects of mind-body therapies on the immune system: Meta-analysis. PLOS One, 9, e100903.
Sengupta, P. (2012). Health impacts of yoga and pranayama: A state-of-the-art review. International Journal of Preventative Medicine, 3(7), 444-458.
Sapolsky, R. M. (2004). Why Zebras Don’t Get Ulcers: The Acclaimed Guide to Stress, Stress-Related Disease, and Coping. New York: Holt and Company.
Woody, A., Hooker, E.D., Zoccola, P.M. & Dickerson, S. S. (2018). Social-evaluative threat, cognitive load, and the cortisol and cardiovascular stress response. Psychoneuroendocrinology, 97, 149-155.
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Sally Dickerson, Ph.D., is a professor of psychology. Her research and teaching focus on how the body responds to stressful circumstances. She also is a yoga teacher (RYT-200) and yoga therapy student at Prema Yoga Institute.
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