- Yoga is a multi-layered ancient set of practices intended to foster personal development.
- Yoga has been shown to improve well-being and alleviate some mental and physical illnesses, though through unclear mechanisms.
- The current review identifies major areas where yoga may affect the mind and body, setting the stage for future investigation.
By Grant Hilary Brenner
Yoga (from Sanskrit “yoke” or “union”) is a darśana (from Sanskrit “to see”), it's traditionally been a path toward enlightenment or freedom from karma or the illusions of suffering. Yoga originated more than 5,000 years ago in the Indus-Sarasvati civilization.1
Yoga, in Sickness and Health
In their recent review in the journal Mindfulness, Pascoe and colleagues (2021) note research showing different forms of yoga increase mindfulness and spiritual well-being, alleviate symptoms of anxiety, stress, pain, and depression in clinical populations, and decrease stress and improve well-being in non-clinical groups. There are many different types of yoga, each integrating different practices and approaches, complicating research.
The researchers included 22 studies culled from multiple databases to identify a broad array of articles. They did not assess the methodology of studies, as the goal of this narrative review was to capture the state of the current literature in the field. From these studies, they identified common proposed mechanisms for yoga’s physiological effects.
13 Areas Where Yoga May Affect Psychobiological Functions
- Interoception: Our ability to perceive the internal state of our bodies is a key factor in health, and for having a healthy relationship with our own bodies, especially in trauma. Mindful interoceptive awareness has been associated with better pain control, along with other benefits. Yoga practice trains people to build interoceptive awareness, as shown in smaller studies. However, more research is needed to better understand how yoga, interception, and health are related.
- Self-Compassion: When we are suffering, being self-critical, experiencing feelings of failure and insecurity, self-compassion allows people to respond with kindness to one’s own state of mind, helping to ground us and foster soothing, positive self-parenting, helpful for well-being. This review found several studies connecting different forms of yoga with increased self-compassion. Research suggests that facing fears of compassion may help people make progress.
- Emotional Regulation: Smoothly managing challenging emotional states is considered a core self-regulatory skill, and part of overall good personality functioning, working with reflective function (mentalization) and executive skills to help us best deploy our resources in times of stress and repose. Authors found no large studies of emotional regulation and yoga, but noted two smaller studies showing improvements in this area in adolescents and yoga practitioners.
- Avoidance/Exposure: Avoidance is a cardinal feature of maladaptive responses to trauma, which, while preventing triggering, leaves people vulnerable to distress when triggers cannot be avoided, and preventing adaptation, or desensitization, to traumatic reminders. Given that many reminders are out of one’s control, internal or in the world, learning to attend to distressing cues without being overwhelmed or needed to steer clear is important for recovery.2
- Rumination: Excessive attention to unpleasant thoughts, memories, experiences, or sensations is associated with less robust coping with trauma and distress. To an extent, the ability to mull over thoughts, make sense of them, cope with emotions as noted above, and move on, is helpful and associated with resilience. Self-compassion has been shown to decrease excessive rumination. The literature on yoga and excessive rumination is inconclusive but a small, controlled study suggests there are benefits for women with depression.
- Meta-Cognition: Related to emotion regulation, executive function and, mentalization—the ability to accurately sense others’ inner states—meta-cognition refers to being able to partially detach from thoughts and feelings, to “let go” of distress and hold suffering more lightly, as well as to reflect upon such experiences mentally, make sense of them, and keep them in context. Yoga has been shown to increase meta-cognition around physical sensations, notably pain. There is no specific research on meta-cognition with yoga, but one study of MSBR which included hatha yoga found increased meta-cognition in depressed patients.
- Attention and Memory: Improving cognitive capacity can help to facilitate positive changes, contributing to good executive function in the deployment of resources. Being able to focus on and remember plans and goals helps in changing habits, making better choices when one is unwell, and sustaining healthy routines. Authors report that multiple studies show improvements in working memory, attention, and inhibitory control with yoga. Less robust findings suggest that yoga may improve some aspects of memory, due to factors that may include improvements in sleep, neural connectivity, and mood.
- Blood Pressure: Elevated blood pressure, when more severe, results in hypertension and requires medical treatment. Less severe elevated blood pressure is associated with high stress, and reductions in blood pressure with relaxation response and better health outcomes. Different forms of yoga have been shown in numerous studies to have a limited impact in reducing blood pressure through different mechanisms, including mindfulness practice and importantly, aerobic exercise.
- Heart Rate: As with high blood pressure, increased heart rate is associated with acute and chronic stress reactions, and also positive excitement and arousal. Similarly, several studies have found that yoga modestly decreases heart rate.
- Heart Rate Variability: Perhaps more than blood pressure or heart rate per se, heart rate variability (HRV) has been shown to be a marker of health and illness.3 Numerous studies of yoga and HRV have found beneficial effects on measures of HRV associated with increased parasympathetic activity via vagal effects and improvements in cardiac parameters as reflected in detailed HRV analysis (i.e. increases in low-frequency HRV are thought to connect with greater parasympathetic response), and with benefits over and above exercise alone.
- Inflammation: More and more research shows that immunological reactions and inflammation are core contributors to a variety of illnesses, including those affecting the central nervous system in association with depression, anxiety, responses to stress and trauma, and a variety of other conditions.4 The authors report a number of studies finding positive changes in cytokines and related markers from yoga practice, including reductions in IL-6 (interleukin-6) and CRP (C-reactive protein), a general measure of inflammation, among others, though other studies were inconclusive or negative.5
- Cortisol: Cortisol is a stress hormone elevated in acute stress and dysregulated in chronic stress. With acute stress, short-term sympathetic nervous system responses are adaptive, allowing for bursts of accelerated activity. However, chronic activation of the stress response system “burns out” responsiveness, a common feature of many psychiatric illnesses. Some yoga studies show beneficial effects on cortisol levels in depressed patients, while others did not. Research reviewed suggested that more comprehensive yoga programs, incorporating the eight components of yoga noted above, may be more effective at modulating cortisol and related stress responses above and beyond exercise alone.
- Neurobiology: Tying together many of the above factors, changes in brain structure including changes in grey matter volume, and function, including measures of connectivity and plasticity, are reflective of differences in mental capacity and related to physiologic changes including regulation of stress systems. A small number of studies look at the impact of yoga on brain structure and/or function. As with experienced meditators, long-term yoga practitioners showed changes in grey matter in key brain areas including increased cortex thickness and hippocampal volume.6 Studies found improved default mode network (DMN) connectivity with yoga practice, associated with better reflective function, as well as potentially increased neural plasticity, required for learning and cognitive flexibility. Yoga and breathwork also may beneficially impact key neurotransmitter levels to produce greater resilience.
The Future of Yoga Research
This narrative analysis broadly reviewed the current state of research on yoga, covering studies in psychiatry and psychology, physiology, and neurobiology, without seeking to isolate and review only high-quality studies. As such, it serves more to clarify directions for future research, creating a reference landscape, than to provide definitive findings. Readers interested in greater nuance can refer to the original study which cites specific studies and identifies the quality of the work, for example, whether they were open or controlled, randomized trials.
The potential benefits of yoga on stress response are likely multifactorial, relating to changes in both physiological and psychological responses to stress, culminating in systemic changes in mind-body function and in how we place ourselves with the social and physical environment, helping to create a preferable overall ecology for our complex lives for those for whom yoga is a good fit.
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1. While there are many forms of yoga, beyond the scope of this discussion, there are generally eight elements: “[C]ultivation of ethical, behavioural and relational values (yama and niyama), physical postures and movements (asana), regulation of breathing (pranayama), control of the senses and inner awareness (pratyahara), concentration of the mind (dharana), meditation (dhyana) and merging of individual consciousness with a greater consciousness (samadhi)” (Pascoe et al, 2021).
2. Learning to temporarily suppress, rather than permanently avoid, gives us more options for coping. Little research has been done with yoga specifically to look at the impact on avoidance, but mindfulness-based stress reduction (MSBR) in one study with a yoga component enabled participants to increase their willingness to sit with unpleasant experiences and was associated with improvement in stress response.
3. HRV is measured by mathematical analysis of the changing time interval between heart beats, as a measure of complexity. Generally speaking, overly rigid or overly variable heart rate may be associated with poor health, both for mental health and cardiac health. By contrast, when HRV shows healthy complexity (akin to a fractal-like mathematical structure), the fight-flight (sympathetic) and recovery (parasympathetic) branches of the autonomic nervous system are in better homeostatic balance.
4. It is well known that people may develop psychiatric illness after certain infections, including common childhood illnesses including strep throat as well as with COVID-19 infection. In addition to direct effects on the brain, gut health affects mental health partially mediated through inflammatory and other mechanisms. “Cytokines” are small protein molecules in the body which carry instructions governing inflammatory responses and interact with chronic stress. Growing evidence finds that depression treatment is associated with decreased inflammation, that anti-inflammatory treatment may alleviate some psychiatric conditions, and that some anti-depressants and psychiatric treatments reduce inflammation in the brain.
5. Whether yoga is beneficial or not appears to depend on the underlying condition, for example helping more with inflammation in heart failure and chronic inflammation more generally but not as clear in cancer survivors or people with rheumatoid arthritis, based on the studies reviewed.
6. Areas of the cortex, the surface of the brain, included the prefrontal cortex, which is involved with executive function and emotion regulation as well as self- and social awareness, and the insula, which is involved with interoceptive awareness and the mind-body connection, as well as improved pain tolerance, while the hippocampus is involved with memory and contextualization of experiences. Some studies found changes in the cerebellum, which is involved with balance and motor coordination, and may help improve overall brain function by helping with coordination among different brain areas.
Pascoe, M.C., J. de Manincor, M., Hallgren, M. et al. Psychobiological Mechanisms Underlying the Mental Health Benefits of Yoga-Based Interventions: a Narrative Review. Mindfulness (2021). https://doi.org/10.1007/s12671-021-01736-z
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