Mindfulness mediates the physiological markers of stress: Systematic review and meta-analysis
Introduction
Stress is common in modern society and is accepted as an important contributing factor to the onset of a range of illnesses, including depression and anxiety (Dantzer, 2012, Iwata et al., 2013, Masi and Brovedani, 2011, Pascoe et al., 2011). Meditation to manage stress is becoming increasingly popular in Western societies. In Australia, about 1 in 6 adults practise meditation (Xue et al., 2007) and in the United States approximately 1 in 13 adults with a medical condition practise meditation (Bertisch et al., 2009). Despite its growing popularity, the neurobiological mechanisms by which meditation may influence stress are not well understood (Pascoe and Crewther, 2016).
There are many forms of meditation and techniques have been classified in several ways (Ospina et al., 2007). A common method of classification distinguishes between open monitoring (OM) and focused attention (FA) meditation, depending on how attentional processes are directed (Chiesa and Malinowski, 2011). More recently, automatic self-transcending (AST) meditation has also be proposed as a third meditation subtype (Travis and Parim, 2017). OM or mindfulness-based meditation involves non-reactive observation of the content of ongoing experience, to become reflectively aware of cognitive and emotional patterns (Raffone and Srinivasan, 2009, Raffone and Srinivasan, 2010). In FA meditation, attention is focused and sustained on a particular object and brought back to the object when the mind has wandered. Thus, the meditator is controlling one's own attention (Cahn and Polich, 2006, Raffone and Srinivasan, 2009, Raffone and Srinivasan, 2010). AST involves a meaningless mantra that the meditator can attend to without effort or concentration, with the aim of the mantra becoming secondary and ultimately disappearing as self-awareness increases. In AST meditation the mind should be free from focus and mental effort (Travis and Shear, 2010). While OM, FA and AST classifications are useful and each of these meditation types show differences in terms of brain functionality (Travis and Shear, 2010), meditation classifications should not be considered to be mutually exclusive, either within a single meditation session or over a life-time of meditation practice (Travis and Shear, 2010). Most meditative techniques lie somewhere on a continuum or orthogonal axes between mindful and concentrative types (Andresen, 2000, Chambers et al., 2009, Chiesa and Malinowski, 2011, Lutz et al., 2008). Indeed, OM and FA have been described as both involving FA, which depending on the meditation type takes different directions (Lutz et al., 2008).
A recent systematic review has shown that various meditation practices influence physiological markers of stress reactivity (Pascoe and Crewther, 2016). Daily life stressors cause pathological arousal and psychological stress resulting in persistent activation of the sympathetic nervous system (SNS) and hypothalamic pituitary adrenal (HPA) axis (Nesse et al., 2016). We have shown in a systematic review that meditation appears to modulate physiological markers of stress in people experiencing depressive symptomatology, particularly when practiced for many hours with a strong focus on breathing (Pascoe and Crewther, 2016). While our review provided preliminary evidence of the beneficial effects of meditation practice on stress reactivity, no meta-analysis has been conducted. Furthermore in our review many studies failed to include an active control (AC) group, which is a significant methodological limitation in this developing filed. Thus, a meta-analysis assessing the impact of meditation on physiological markers of stress in randomised controlled trials (RCTs) with an AC group is both timely and important. In this study we aimed to conduct a meta-analysis of RCTs investigating the effects of meditation practices, including AST, FA and OM subtypes, compared to an AC, on markers of physiological stress.
Section snippets
Materials and 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
A PRISMA flow-diagram shows the selection of papers for inclusion and exclusion (Fig. 1). 2041 articles were retrieved. Of these 1273 were duplicates and a further 80 were thesis, books or conference proceedings. Ultimately 45 were included. Additional data was provided by one author (Wahbeh et al., 2016).
Study characteristics
Study specifications are listed in Table 1. Five studies compared meditation with two AC conditions (Carlson et al., 2015, Jung et al., 2015, Lipschitz et al., 2013, Oken et al., 2010, Wahbeh
Discussion
We conducted a meta-analysis of RCTs investigating the effects of meditation, including AST, FA and OM subtypes, compared to an AC on markers of physiological stress. We included 45 studies which examined the relationship between meditation and cortisol, HR, BP, cytokine and lipid levels. Lipids were included as high cholesterol levels are associated with the accumulation of cholesterol in macrophages and other immune cells, which promotes inflammation (Tall and Yvan-Charvet, 2015), and as
Conflict of interest
The authors declare no conflict of interest.
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