Implications for practice and research

• The findings highlight the use of meta-analysis as a valuable tool to evaluate mindfulness interventions.

• The research provides substantial support for mindfulness approaches in treating depression in the context of other symptoms and disorders.

• Evidence-based indications for practice are crucial given that up to 75% of patients with depression do not receive treatments based on scientific evidence.1

Context

Depression is one of the most common psychological disorders and is frequently comorbid with other psychiatric conditions. Mindfulness-based interventions have become increasingly popular mainstays of treatment and adjuncts to empirically established therapies.

Findings

The most impressive effect sizes were for exposure based cognitive therapy (d = 2.09), followed by mindfulness-based stress reduction (d = 1.92), acceptance-based behaviour therapy (d = 1.33), and stress less with mindfulness (d = 1.31). Effect sizes were associated with intervention length but not methodological quality.

Commentary

A problem in interpreting the meta-analysis is that mindfulness is typically combined with other interventions (eg, hatha yoga, exposure therapy) so its unique contribution to treatment is difficult to assess. Conclusions about the impact of mindfulness are limited in the absence of dismantling studies that examine the unique contribution of mindfulness versus other treatment components. Moreover, studies typically do not evaluate theories or mechanisms of change. Nor do they assay mindfulness over the course of treatment and document a link between mechanism and outcome, thereby calling for caution in making causal inferences about mindfulness versus nonspecific effects in explaining treatment gains.

Interventions represented in the meta-analysis differ in how they define and teach mindfulness (e.g., concentration meditation, loving-kindness meditation), which may account for different outcomes across studies. For example, the authors contend that mindfulness interventions ‘aim to help the individuals relax their minds and, therefore, achieve a state of calmness, peace, and happiness’. However, a relaxed mind is not prerequisite to successful mindfulness practice, as most definitions emphasise non-judgement and acceptance, regardless of the level of relaxation achieved.

The author-created 11-item Quality Rating Index summed possible indicators of strength of treatment methodology. However, some items are arguably more important to methodological integrity (eg, double-blinded procedure) than others that pertain to the description of the methodology (eg, clear definition of measures, description of statistical analyses). Accordingly, the relation between methodology and outcome will likely vary as a function of the variables selected or combined for analysis.

The authors allude to adverse effects (eg, psychotic features, impaired reality testing, anxiety) following mindfulness interventions. However, caveats in this regard should be balanced with the appreciation for the fact that such experiences may have been present prior to treatment, and it may be difficult to pinpoint the cause of adverse effects in multi-component treatments.

The odds patients will present with more than one diagnosis are quite high.2 Accordingly, the meta-analysis, which considers depression in the context of other psychiatric disorders, is in keeping with the current move toward transdiagnostic approaches. Indeed, it is often imperative that clinicians address more than one disorder, as shared underlying vulnerabilities across disorders, functional relationships among disorders, or other systematic covariates call for addressing multiple symptoms.

That said, the effect sizes reported by Klanin-Yobas and colleagues may be confounded with: (a) the unique combination and interaction of symptoms treated that vary across studies; (b) the recalcitrance of treating certain disorders relative to others; and (c) the fact that comorbid depression may be particularly likely to inhibit treatment success in the presence of certain disorders such as ADHD.3 Knowledge of whether treatment effects were clinically significant (eg, fewer patients diagnosed with major depression) would be useful to practicing clinicians. Still, by informing readers about the efficacy of mindfulness in treating depression in the context of other symptoms and disorders, the authors have provided valuable input regarding a question of paramount interest to practitioners and researchers alike: ‘What works, for whom, and under what conditions?’