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 Jenny Gu a,b , Clara Strauss b,c , Rod Bond a , Kate Cavanagh a,b, ⁎ a School of Psychology, University of Sussex, Falmer, East Sussex, BN1 9QH, UK b Sussex Mindfulness Centre, Research and Development Directorate, Hove, BN3 7HZ, UK c Sussex Partnership NHS Foundation Trust, Hove, BN3 7HZ, UK 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 article info Article history: Received 22 September 2014 Received in revised form 16 December 2014 Accepted 22 January 2015 Available online 31 January 2015 Keywords: Mindfulness Mechanisms Mediation Structural equation modelling Meta-analysis Mental health 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. © 2015 Published by Elsevier Ltd. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Hypothesised mechanisms underlying mindfulness-based interventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Methods of studying the mechanisms underlying mindfulness-based interventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. The current study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Clinical Psychology Review 37 (2015) 1–12 ⁎ Corresponding author at: School of Psychology, University of Sussex, Falmer, East Sussex BN1 9QH, UK. Tel.: +44 1273 877395; fax +44 1273 678058. E-mail address: kate.cavanagh@sussex.ac.uk (K. Cavanagh). http://dx.doi.org/10.1016/j.cpr.2015.01.006 0272-7358/© 2015 Published by Elsevier Ltd. Contents lists available at ScienceDirect Clinical Psychology Review