ReviewYoga, mindfulness-based stress reduction and stress-related physiological measures: A meta-analysis
Introduction
The daily demands associated with modern life cause arousal and can lead to psychological stress and activation of the stress response, or ‘fight-or-flight’ response (Nesse et al., 2016). The stress response, which can be defined as real or perceived threats to homeostasis or safety/well-being (Herman et al., 2016) is adaptive in situations of imminent threat. Persistent activation of the ‘fight-or-flight’ response can be associated with the onset of psychiatric disorders such as anxiety and depression (Iwata et al., 2013, Ventriglio et al., 2015).
The practice of yoga is aimed at achieving a union of mind, body and spirit and has become popular in recent years as a form of stress management in Western cultures (Penman et al., 2012). Meta-analysis has shown that yoga practice effectively decreases depressive and anxious symptomatology (Cramer et al., 2013). While there is no definitive taxonomy of yoga, as the many forms of the practice have unique theoretical underpinnings and approaches (Ospina et al., 2007), common elements are shared by many forms, such as controlled breathing, meditative techniques and physical postures (Farmer, 2012, Pflueger, 2011, Travis and Pearson, 2000). Approximately 10% of the population were practising yoga in the United States in 2012 (Clarke et al., 2015). In England, approximately 1.28% of the population were practising it in 2006/08 (Ding and Stamatakis, 2014). Medical practitioners often prescribe yoga to their patients, (Nerurkar et al., 2011) with as many as 77% of surveyed Australian practitioners referring their patients to a yoga therapist (Wardle et al., 2014).
Mindfulness-based stress reduction (MBSR), developed by Kabat-Zinn in the 1970s (Miller et al., 1995), is a group program that uses a combination of mindfulness meditation, body awareness and yoga asanas with the aim of increasing mindfulness (Praissman, 2008). Typically, MBSR is run across eight sessions with at least one session plus a day-long retreat including yoga asanas, as well as home practice that may or may not include further yoga asanas, thus the practice of yoga asanas is part of a wider program in MBSR (Praissman, 2008). MBSR has been promoted to clinicians a safe and effective technique to reduce stress and anxiety in diverse patient populations (Praissman, 2008).
In spite of the popularity of practices that include yoga asanas in the management of stress, research in this area is in its infancy and the neurobiological effects of such practices are still not well elucidated. Given the frequency with which people are choosing to engage in yoga asanas and MBSR for stress management, it is important to validate and understand the neurobiological effects of these practices. Some researchers have hypothesised that practices including yoga may decrease stress reactivity and thus result in overall improved health and wellbeing (Riley and Park, 2015). We have shown previously in a systematic review that yoga asanas appear to modulate the regulation of the sympathetic nervous system (SNS) and hypothalamic-pituitary-adrenal (HPA) system in people experiencing depressive symptomatology, indicated by decreases in blood pressure (BP), heart rate (HR), cortisol or cytokine levels (Pascoe and Bauer, 2015). While this previous review provided preliminary evidence of the beneficial effects of yoga asanas on stress activity, to date no meta-analysis has been conducted. Furthermore, our previous review was limited to a particular population and highlighted that many studies fail to include an active control (AC), a limitation in this developing field. Therefore, we aim to conduct a meta-analysis investigating the effects of yoga asanas, including MBSR, on stress reactivity, in randomised controlled trials (RCTs) that include an AC group, in all populations. We discuss the relevance of these findings in the context of stress-related depression.
Section snippets
Methods
This study was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (Moher et al., 2010). A prospective protocol for the systematic review was not previously published.
Study selection
Initially 1329 articles were retrieved. Of these, 538 were duplicates and a further 40 were theses, leaving 789 for screening. One study collected cortisol outcomes but did not report these (Cohen et al., 2011). Title/abstract screening excluded 706, 83 remained for full-text review and ultimately 42 RCTs were included, consisting of 2944 participants. A PRISMA flow diagram shows the selection of papers for inclusion and exclusion (Fig. 1).
Study characteristics
Study specifications are listed in Table 1. In cases
Discussion
In this review we included 42 studies which examined the relationship between interventions including yoga asanas and physiological measures of stress. Outcomes included cortisol, autonomic measures, cytokines and lipid levels.
Conclusion
While yoga practice has become a popular method of stress management, its neurobiological underpinnings are not well understood. This is the first meta-analysis of RCTs with ACs demonstrating that yoga asanas practice appears to have inhibitory effects on physiological stress, as demonstrated by decreased cortisol, decreased BP and cytokine levels. The current meta-analysis included a broad range of populations, suggesting that the observed effects are not specific to a particular population.
Conflicts of interest
The authors declare no conflicts of interest.
My co-authors have all contributed to this manuscript and approve of this submission. Neither this manuscript nor substantial parts of it are under consideration for publication elsewhere, have been published nor made available elsewhere in a manner that could be construed as a prior or duplicate publication of the same content. There is not a manuscript of related content (e.g. from the same study with the same or very similar primary exposure and
Acknowledgments
Author contributions are as follows: MCP conceived the study including data sources and search strategy, conducted the systematic search, performed study selection, extracted data, performed data synthesis and wrote the manuscript. DRT conceived the study including data sources and search strategy and critically appraised the manuscript. CFK conceived the study including data sources and search strategy and critically appraised the manuscript. All authors take responsibility for the contents of
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