Do workplace-based mindfulness meditation programs improve physiological indices of stress? A systematic review and meta-analysis (original) (raw)
Highlights
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Mindfulness-based interventions (MBIs) lowered high and low diurnal cortisol slopes. - •
MBIs increased measures of heart rate variability. - •
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MBIs increased antibody response to a viral vaccine. - •
MBIs reduced C-reactive protein concentrations.
Abstract
Objective
Mindfulness-based interventions (MBI) have been related with improved job satisfaction, wellbeing, health, and reduced workplace stress with employees. However, until now, synthesis of the evidence of the effect of MBIs on physiological indices associated with stress and ill-health has been lacking. Therefore the current systematic review aimed to synthesise the literature from employee samples to provide guidance for future investigations in terms of which physiological indicators and biological systems may be most impacted by MBIs.
Methods
Electronic databases were searched. Studies that conducted a mindfulness-based program with an employee sample, which targeted workplace stress or work engagement, and measured a physiological outcome were selected for inclusion. Studies using either a between-group or within-group design were included. Nine papers were found to meet the inclusion criteria for our systematic review and meta-analysis of the literature.
Results
MBIs were found to be effective in reducing cortisol production, as indicated by lowered high and low diurnal cortisol slopes. However, no changes were found for cortisol awakening response or concentrations for single a.m. and p.m. time-points. MBIs also improved autonomic balance, assessed by heart rate variability coherence measures, but not blood pressure. Sympathetic nervous system reactivity as measured by salivary alpha amylase was also reduced following MBI. While aspects of immune function were also improved following MBIs, specifically, increased antibody response to a viral vaccine and reduced C-reactive protein concentrations, each of these outcomes were only assessed in a single study.
Conclusion
Taken together, the findings suggest that MBIs are a promising avenue for intervention for improving physiological indices of stress. Our findings suggest that changes in daytime cortisol secretion and HRV coherence may be particularly influenced by MBIs. Future studies should aim to assess multiple physiological indices to confirm the current findings and further improve current understanding of which biological systems (and indices within these systems) show responses indicative of reduced stress due to MBI.
Introduction
Workplace stress is associated with costs to individuals, organizations, and the community. It is consistently linked with poorer health outcomes, including cardiovascular disease [1,2], psychosomatic problems, musculoskeletal disorders [3] and self-reported health [4,5]. Workplace stress is also associated with mental health issues, including depression and anxiety disorders [6,7]. Finally, it is also related to a number of pre-clinical markers of ill-health, including indicators of the immune system [8], cardiovascular health [9] and the hypothalamic-pituitary-adrenal (HPA) axis [10,11]. In addition to health concerns, the cost of workplace stress extends to the employer due to higher turnover rates [12,13], increased absences [14] and decreased work engagement [15]. Given the associated costs of workplace stress to individuals and society it is important to determine the most appropriate interventions to reduce it.
Interventions that are suitable to the workplace environment are rare [16], but a contemporary intervention with promising results across different populations and settings, including the workplace, is mindfulness meditation [17,18]. This is the act of purposefully paying attention to the present moment and being aware of mental states and processes with a sense of openheartedness, curiosity and kindness, and without judgement [19].
An increasing body of evidence demonstrates the effectiveness of mindfulness-based interventions (MBI) in improving job satisfaction, wellbeing, health, and reducing workplace stress [[20], [21], [22]]. However, a synthesis of the effects of MBIs on physiological indicators of workplace stress and ill-health is lacking.
Recent reviews conclude that MBIs improve dysregulated cortisol responses and immune functioning [[23], [24], [25]]; however, these reviews investigated patient populations and healthy adults, rather than MBIs in workplace settings. Previous research has shown different forms of chronic stress (e.g. work stress, caregiving, death/loss) have disparate effects on physiological outcomes [26,27]. Moreover, the few reviews that have considered employees and include physiological indicators, consider indices of multiple biological systems (e.g., the immune system, hypothalamic–pituitary–adrenal axis) together [20,28]. This coarse, unidimensional approach may contribute to the mixed findings of the effects of MBIs on physiological outcomes [20]. In the present review, we will synthesise the effects of MBI on discrete biological systems.
Inclusion of physiological indices are important to consider as they may act as pre-clinical markers of the development of ill-health [29]. When a stressor is experienced biological systems are activated to prepare the body to overcome the stressor. For example, the hormone cortisol, a primary product of the HPA axis, is associated with cardiovascular mortality and depression [[30], [31], [32]]. Likewise, C-reactive protein (CRP) and interleukin 6 (IL-6), two biomarkers of systemic inflammation are predictors of depression [33]. Increased CRP levels are also associated with increased risk of myocardial infarction [34]. Lower heart-rate variability (HRV), an indicator of cardiovascular function, is linked to all-cause mortality and cardiovascular disease [35]. By considering physiological indicators of stress we can gain a greater understanding of the potential mechanisms of action of MBI on these biological systems.
A relevant model that can explain how MBIs modify dysregulated physiological responding is the integrated specificity model. The central tenant of the model is that the cognitive appraisal of a stressor is associated with distinct emotions, which in turn results in a specific, integrated pattern of physiological responses [36]. For example, threat emotions have been found to explain 56% of the variance in cardiovascular reactivity to an acute stressor [37], while social evaluative threat has also been associated with increased cortisol and pro-inflammatory responses [38]. Mindfulness may be a particularly effective resource as it increases an individual's ability to experience stressors without automatically perceiving them as a threat [39]. Indeed, higher levels of dispositional mindfulness have been found to moderate the effects of a social evaluative stressor on negative affect and cortisol responses [40]. The positive relationships observed between dispositional mindfulness and health [[20], [21], [22]] may be due to the MBIs reducing the experience of threat or harm emotions and the subsequent adverse physiological reactions these emotions provoke. However, as physiological indicators of stress have been included as outcomes in several recent studies, the first step to understanding these posited relationships is to synthesise this literature to assess the efficacy of MBI's in promoting adaptive physiological responses.
Given the increasing popularity and the potential for MBIs to be an effective and easily-implemented intervention for the workplace, it seems timely to provide a review of the literature investigating MBIs and physiological indicators of stress and ill-health. Previous reviews and meta-analyses have recommended the use of objective measures in future studies [18,21]; an aim of the present review is to synthesise the literature from employee samples to provide guidance for future investigations in terms of which physiological indicators and biological systems may be most impacted by MBIs.
Section snippets
Method
The current systematic review and meta-analysis followed the PRISMA guidelines for systematic reviews and meta-analyses [41]. The protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO), under registration number CRD42016052826.
Study characteristic
Nine papers published between 2003 and 2015 investigated the effects of a mindfulness intervention on pre-clinical markers of ill-health. The characteristics of the included studies are presented in Table 1. Of the ten individual studies included in the nine papers, there were a total of 26 comparisons. Total sample size was 812 after attrition, 86 participants dropped out across the studies. Individual studies ranged from 18 to 239 participants (M = 81.20, SD = 74.65). There were 409
HPA axis measures
One study used a within group comparison of the mindfulness intervention while four other investigations utilised mixed within-between designs that incorporated a control group. The four studies that compared the effects of mindfulness training against a control group across time on HPA axis indices (i.e., CAR, 0 and 30 min post waking, high and low diurnal cortisol slopes, average diurnal cortisol concentration, pre-lunch and bedtime cortisol) reported inconsistent findings. We conducted a
Discussion
The current systematic review and meta-analysis aimed to provide a synthesis of the literature of the effectiveness of MBIs in improving physiological indices of stress in employee populations. The findings indicate that MBIs were effective in increasing high and low diurnal cortisol slopes, which is suggestive of a better regulated HPA axis. The findings regarding cardiovascular indicators were mixed, with MBIs improving autonomic balance as assessed by the HRV coherence ratio measure but
Conclusion
Considered together, the studies reviewed suggest that MBIs are a promising avenue for encouraging adaptive physiological responses. In particular, the diurnal cortisol slopes, HRV coherence, SNS activity and some indicators of immunity differed pre-post intervention. Our review indicates that mindfulness may act on discrete physiological systems differently with the preliminary evidence suggesting that the HPA axis in particular, is more consistently influenced than the cardiovascular, and SNS
Conflict of interest
The authors declare that they have no conflict of interest.
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