Elsevier

Clinical Psychology Review

Volume 37, April 2015, Pages 1-12
Clinical Psychology Review

How do mindfulness-based cognitive therapy and mindfulness-based stress reduction improve mental health and wellbeing? A systematic review and meta-analysis of mediation studies

https://doi.org/10.1016/j.cpr.2015.01.006Get rights and content

Highlights

  • We systematically review mediation studies on mechanisms of MBCT and MBSR.

  • We statistically integrate mediation data using two-stage structural equation modelling.

  • Strong consistent evidence for reactivity as a mechanism of MBCT and MBSR

  • Moderate consistent evidence for mindfulness, rumination and worry as mechanisms

  • Mindfulness, rumination and worry are significant mediators for clinical outcomes.

Abstract

Given the extensive evidence base for the efficacy of mindfulness-based stress reduction (MBSR) and mindfulness-based cognitive therapy (MBCT), researchers have started to explore the mechanisms underlying their therapeutic effects on psychological outcomes, using methods of mediation analysis. No known studies have systematically reviewed and statistically integrated mediation studies in this field. The present study aimed to systematically review mediation studies in the literature on mindfulness-based interventions (MBIs), to identify potential psychological mechanisms underlying MBCT and MBSR's effects on psychological functioning and wellbeing, and evaluate the strength and consistency of evidence for each mechanism. For the identified mechanisms with sufficient evidence, quantitative synthesis using two-stage meta-analytic structural equation modelling (TSSEM) was used to examine whether these mechanisms mediate the impact of MBIs on clinical outcomes. This review identified strong, consistent evidence for cognitive and emotional reactivity, moderate and consistent evidence for mindfulness, rumination, and worry, and preliminary but insufficient evidence for self-compassion and psychological flexibility as mechanisms underlying MBIs. TSSEM demonstrated evidence for mindfulness, rumination and worry as significant mediators of the effects of MBIs on mental health outcomes. Most reviewed mediation studies have several key methodological shortcomings which preclude robust conclusions regarding mediation. However, they provide important groundwork on which future studies could build.

Introduction

Although there are diverse definitions of mindfulness, it is commonly and operationally defined as the quality of consciousness or awareness that arises through intentionally attending to present moment experience in a non-judgemental and accepting way (Kabat-Zinn, 1994). Mindfulness originates from Eastern traditions and its recent popularity in Western psychology is largely due to the development and wide-spread application of standardised mindfulness-based interventions (MBIs), which integrate the essence of traditional mindfulness practice with contemporary psychological practice, in order to improve psychological functioning and wellbeing. The two most extensively employed and evaluated MBIs are mindfulness-based stress reduction (MBSR; Kabat-Zinn, 1982) and mindfulness-based cognitive therapy (MBCT; Segal et al., 2002, Segal et al., 2013), both of which are eight-week group-based therapies which teach mindfulness skills through a range of formal and informal mindfulness practices. These include mindfulness of breath, thoughts, bodily sensations, sounds, and everyday activities. A growing body of robust evidence from randomised controlled trials (RCTs) has demonstrated that MBIs are effective in improving a range of clinical and non-clinical psychological outcomes in comparison to control conditions, including anxiety (Green and Bieling, 2012, Hofmann et al., 2010), risk of relapse for depression (Kuyken et al., 2008, Teasdale et al., 2000), current depressive symptoms (Strauss, Cavanagh, Oliver, & Pettman, 2014), stress (Chiesa & Serretti, 2009), chronic pain (Grossman, Tiefenthaler-Gilmer, Raysz, & Kesper, 2007), quality of life (Godfrin and van Heeringen, 2010, Kuyken et al., 2008), psychological symptoms in patients with cancer (Ledesma & Kumano, 2009) and retrieval of specific autobiographical memories (Williams, Teasdale, Segal, & Soulsby, 2000), a reliable cognitive marker of depression (e.g. Brittlebank, Scott, Williams, & Ferrier, 1993).

Other notable interventions which involve mindfulness principles alongside other components include acceptance and commitment therapy (ACT; Hayes & Wilson, 1994) and dialectical behavioural therapy (DBT; Linehan, 1993). A consensus has not yet been reached regarding the similarity between MBSR and MBCT and these alternative interventions (Chiesa & Malinowski, 2011). However it is clear that alternative interventions differ considerably from MBSR and MBCT and each other in the duration and frequency of mindfulness practice involved, and the inclusion of mindfulness psychoeducation and non-mindfulness therapeutic ingredients. Therefore, the current review will focus solely on MBCT and MBSR to ensure consistency across studies and will use the term MBI to refer to these two interventions. These interventions have much in common in their core elements, have published therapy protocols that are adhered to in research trials and have generated the large body of evidence.

Section snippets

Hypothesised mechanisms underlying mindfulness-based interventions

Compared to the extensive evidence base for the effectiveness of MBSR and MBCT, relatively few studies have tested the mechanisms of action which causally connect changes that occur during MBIs with psychological outcomes. Kazdin (2007) emphasises several clinically relevant reasons why establishing the mechanisms of psychotherapies is crucial. These include being able to optimise therapeutic effects through enhancing active components of interventions, distinguishing between the specific and

Methods of studying the mechanisms underlying mindfulness-based interventions

To understand how change occurs during interventions, conducting mediation analyses to study the indirect influence of a treatment (X) on an outcome (Y) through a mediator (M), or intervening variable, is an essential first step (Kazdin, 2007). There are over a dozen methods of mediation analysis, most of them testing the statistical significance of a sequence of linear regression models (Baron & Kenny, 1986), or using structural equation modelling (SEM), which allows simultaneous examination

The current study

Despite systematic reviews long being advocated as a method for investigating the mediators attributed to interventions (Shadish, 1996), as interpretation of what explains a phenomenon cannot emerge from a single study (Kazdin, 2007), there are no known systematic reviews of the mechanisms of MBIs reviewing only mediation studies. Researchers have also advocated integrating meta-analytic techniques with SEM to statistically evaluate and synthesise evidence for mediation across multiple studies

Identification and selection of studies

A comprehensive search of published studies up to 10/01/2014 was conducted using the following electronic databases: PsycInfo, Scopus, Web of Knowledge, PsycArticles, ASSIA and Science Direct. The search term was: (“mindfulness based cognitive therapyORmindfulness based stress reductionOR MBSR OR MBCT) AND (mechanism* OR mediat* OR predict* OR process* ORstructural equation modellingOR caus* OR path* OR correlat* OR relationship OR associat*).

Inclusion and exclusion criteria

Any study published in English which used

Study flow and characteristics

The search identified 1547 articles, 533 of which were duplicates. Of the remaining 1014 papers, 845 were excluded based on the title or abstract, thus the number of full-text articles assessed for eligibility was 169. The final number of studies meeting the inclusion criteria and included in the systematic review was 20. One RCT (Batink, Peeters, Geschwind, van Os, & Wichers, 2013) conducted two separate mediation analyses on subgroups in their sample and were included as two separated

Discussion

This paper's aims were threefold. First, it aimed to systematically review mediation studies in the literature on MBIs, in order to identify the mechanisms underlying MBCT and MBSR's effects on psychological functioning and wellbeing. Second, it aimed to evaluate and provide narrative summaries of the strength of evidence for each identified mechanism. Third, it aimed to conduct TSSEM analyses, to statistically synthesise evidence for mechanisms of the effects of MBIs on mental health outcomes

Conclusions

The empirical investigation of the mechanisms of change underlying the effects of MBIs on psychological functioning and wellbeing is a complex yet crucial path on which to embark in order to improve the quality, delivery and effectiveness of the interventions, develop the theoretical underpinnings of mindfulness and MBIs and inform the direction of future research. The current study is the first to systematically review mediation studies to identify and evaluate the strength and consistency of

Role of funding sources

This research was partly funded by the Economic and Social Research Council and Sussex Partnership NHS Foundation Trust in a joint Doctoral Training Scholarship provided to the first author (grant number ES/J500173/1).

Contributors

JG designed the study, developed the search strategies, conducted the literature searches and wrote the first draft of the manuscript, under the supervision of CS and KC. JG conducted the two-stage structural equation modelling analyses in collaboration with RB. All authors contributed to and have approved the final manuscript.

Conflict of interest

All authors declare that they have no conflict of interest.

Acknowledgements

This research was partly funded by the Economic and Social Research Council (grant number ES/J500173/1) and Sussex Partnership NHS Foundation Trust in a joint Doctoral Training Scholarship provided to the first author.

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