Mindfulness-based programmes (MBPs), suggested to improve work and academic performance, are increasingly used in occupational and educational settings. This thesis advances the field by synthesising the evidence, optimising the operationalisation of work performance, providing preliminary data on MBPs’ effectiveness and mechanisms for work performance, and testing acceptability and feasibility for future trials.

First, I led a systematic review and meta-analysis which aimed to map how work performance has been operationalised in randomised controlled trials (RCTs) of MBPs and to assess the impact of MBPs on adults’ academic and work performance. The pre-registered primary outcome was task performance, a key aspect of work performance, up to 4 weeks after the intervention (PROSPERO: CRD42020191756). Secondary outcomes were the remaining aspects: contextual performance, adaptive performance, and counterproductive work behaviours. Pairwise random-effects meta-analyses were used to calculate Hedges’ g. A total of 47 RCTs with 5041 participants were included. Adaptive performance outcomes were collected most frequently. There was no support for MBPs significantly improving task performance (7 RCTs, 454 participants, Hedges’ g = 0.52, 95% CI -0.03 to 1.07, p = 0.06) compared with passive control groups. However, MBPs statistically significantly improved adaptive performance and contextual performance. There were an insufficient number of RCTs to allow meta-analysis comparing MBP to active control interventions. All bar one RCT demonstrated high risk of bias. Confidence in the review results was ‘low’ to ‘very low’, according to the Grading of Recommendations Assessment, Development and Evaluation (GRADE) criteria.

Second, I led a feasibility RCT which evaluated whether improved cognitive control and/or enhanced mental health may be mechanisms underpinning the effect of MBPs on work performance. Two hundred and forty-one employees were recruited from eight employers. The participants were randomised on 1:1 basis to the offer of a four-week, self-guided, digitally delivered intervention of either the Be Mindful MBP or a light physical exercise programme (control intervention). We assessed the acceptability of interventions and trial procedures, and estimated effect sizes to inform sample size calculations for a later-stage trial. The primary effectiveness outcome was self-reported work performance at post-intervention measured using the Work Role Functioning Questionnaire. Secondary outcomes included depression, anxiety, stress, and cognitive processes hypothesised to be targeted by mindfulness, including decentering and executive functions. All outcomes were assessed at pre-intervention, post-intervention, and 12-week follow-up. The trial protocol was pre-registered (NCT04631302) and published. We concluded that a full-scale trial would be feasible and acceptable, based on recruitment and retention rates. Yet, a full-scale trial may not be warranted: the MBP, compared to light physical exercise, offered negligible benefits for work performance at post-intervention (Cohen’s d = 0.06) and 12 weeks later (Cohen’s d = 0.02). For the potential mechanisms, we observed similarly small effect sizes for the differences between the MBP and the alternative intervention on mental health and cognitive control outcomes. Both interventions improved mental health outcomes compared to baseline.

In conclusion, while MBPs may have some potential in enhancing some aspects of work performance when compared to passive control groups, the results of this thesis suggest the evidence is of low quality. Furthermore, the effectiveness of MBPs compared to alternative interventions, like physical exercise, remains uncertain. We found no evidence to suggest cognitive control could be a mechanism underlying MBPs effects on work performance, when compared to light physical exercise. These findings underscore the importance carefully operationalising work performance and conducting high-quality trials to establish the impact of MBPs on work performance in occupational settings.