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Hempel S, Taylor SL, Marshall NJ, et al. Evidence Map of Mindfulness [Internet]. Washington (DC): Department of Veterans Affairs (US); 2014 Oct.
The systematic review search identified 332 citations. This included 81 unique systematic reviews meeting the inclusion criteria.6-86 The results are presented in a bubble plot and a text summary.
Evidence Map of Mindfulness
The bubble plot broadly summarizes mindfulness intervention systematic reviews published to February 2014 and shows the clinical conditions addressed in reviews (bubbles), the estimated size of the literature (y-axis), the effectiveness trend according to reviews (x-axis), and the number of reviews (bubble size) per clinical condition. Colors: green (various mindfulness interventions), pink (MBSR), purple (MBCT), blue (MBSR+MBCT), yellow (unique mindfulness-based intervention)
EXECUTIVE SUMMARY
The evidence map used the clinical topics addressed in existing systematic reviews. Reviews varied widely in scope. While some reviews evaluated specific interventions, such as MBSR following the original 8-week structured program, others included a large range of mindfulness-based interventions such as MBCT, mindfulness meditation, or complex interventions where mindfulness was one of many components. In addition, review authors varied in their definition of “mindfulness intervention.” The evidence map displays the topics of systematic reviews; primary research studies may have contributed to multiple systematic reviews. All depicted dimensions are estimates and can only provide a broad overview of the evidence base.
Areas with the Largest Research Base
We identified 9 systematic reviews that addressed health benefits of mindfulness interventions (health-all) and the largest review included 109 RCTs. The largest review, a comprehensive meta-analysis of 209 mindfulness-based therapy studies, reported positive effects in pre-post comparisons and across controlled studies but not effects seen in RCTs specifically (ie, the most robust research design).47 The review included mindfulness meditation-based interventions and excluded studies that examined mindfulness as part of another treatment, such as cognitive behavior protocol, Acceptance and Commitment Therapy, Dialectical Behavior Therapy, and Loving-Kindness Meditation. An AHRQ report on meditation practices included 50 RCTs evaluating mindfulness-based approaches, including mindfulness meditation techniques not further described, Zen Buddhist meditation, MBCT, and Vipassana meditation.87 Individual study results varied, the quality of included studies was rated as poor, and no pooled result across studies was reported. The report stated further that in cardiovascular diseases, indirect comparisons showed that there were no significant differences in measures of anxiety between yoga and MBSR. A 2004 meta-analysis included 7 RCTs and reported a positive effect for mental health (Cohen's d 0.54; 95% confidence interval (CI) 0.35, 0.74; p<0.001; 7 RCTs) but physical health estimates were not pooled separately from other study designs and the statistical significance of the individual study results was not reported.44 Six additional reviews included between 26 and zero mindfulness-based intervention RCTs, with varying individual study results, and did not report a pooled treatment estimate for RCTs.
A Campbell Collaboration systematic review addressed health benefits of MBSR (health-MBSR) and included 31 RCTs.8 The review only included training programs based on the protocol elements specified by Kabat-Zinn (body-scan exercises, mental exercises focusing attention on breathing, physical exercises focusing on the awareness of bodily sensations, and the practice of being fully aware during everyday activities). The review reported positive effects on the combined outcome mental health (SMD 0.53; 95% CI -0.43, 0.64; 26 RCTs), measures of personal development (0.50; 95% CI 0.35, 0.66; 12 RCTs), quality of life (0.57; 95% CI 0.17, 0.96; 4 RCTs), mindfulness (0.70; 95% CI 0.05, 1.34; 7 RCTs), and somatic health (0.31; 95% CI 0.10, 0.52; 10 RCTs) compared to waitlist and usual care control groups. The review concluded that MBSR has a moderate and consistent effect on a number of measures of mental health for a wide range of target groups and appears to improve measures of personal development such as empathy and coping, enhances mindfulness and quality of life, and improves some aspects of somatic health. The review also noted that there is a lack of data on social function, work ability, and long-term effects.
We identified 2 systematic reviews that addressed psychological wellbeing (psychological-all) and the largest review included 36 RCTs. The largest review was based on an AHRQ report on meditation programs for psychological stress and wellbeing, which classified MBSR, MBCT, Vipassana, Zen, and other mindfulness meditation as mindfulness-based. The review reported positive effects for anxiety (Cohen's d 0.38; 95% CI 0.12, 0.64; at 8 weeks; 0.22; 95% CI 0.02, 0.43; at 3-6 months; 8 RCTs total), depression (0.30; 95% CI -0.00, 0.59; at 8 weeks; 0.23; 95% CI 0.05, 0.42; at 3-6 months; 10 RCTs total); and pain (0.33; 95% CI, 0.03 to 0.62; 4 RCTs) compared to control interventions matched in time and attention.43 The AHRQ report also showed a positive effect on negative affect (general anxiety, stress/distress, and depression outcomes combined; standardized mean difference (SMD) -0.34 (95% CI -0.53, -0.14; 10 RCTs).3 Data on stress/distress varied by comparator, the pooled results for the outcomes mental health related quality of life, positive affect, and sleep were negative, and there was insufficient evidence for positive mood, attention, substance use, eating habits, and weight. There was no evidence that meditation programs were better than any active treatment (ie, drugs, exercise, and other behavioral therapies). The review concluded that meditation programs can result in small to moderate reductions of multiple negative dimensions of psychological stress. An additional review evaluated the effects of mindfulness meditation in non-clinical samples.9 The pooled effect across psychological variables was statistically significant for MBSR (r 0.29; 12 RCTs) and for mindfulness meditation (r 0.22; 5 RCTs) compared to inactive control groups. The review's conclusions were centered on differences in effects between MBSR and “pure” mindfulness meditation interventions seen across the multitude of included studies; the authors suspected that effect sizes in MBSR might be partly inflated by effects not attributable to the mindfulness meditation component.
Two systematic reviews addressed MBSR and psychological variables (psychological-MBSR) and the largest included 17 RCTs. The largest review reported across all psychological outcomes an effect size of Cohen's d 0.396 (95% CI 0.19, 0.61; p<0.001; 17 RCTs) compared, primarily, to waitlist.20 Stratified by comparator, active treatments (progressive muscle relaxation, cognitive behavioral group therapy, or massage) were not statistically significantly better than MBSR (-0.249; 95% CI -0.731, 0.234; 3 RCTs). MBSR was not statistically significantly better than minimal contact (0.258; 95% CI -0.192, 0.709; 2 RCTs). The effect size estimate of MBSR compared to waitlist was 0.542 (95% CI 0.334, 0.749; 12 RCTs). The review considered 48 different psychological variables and reported positive pooled effects for stress (0.792; 95% CI 0.371, 1.123; 4 RCTs), distress (0.547; 95% CI 0.193, 0.901; 6 RCTs), depression (0.512; 95% CI 0.164, 0.861; 5 RCTs), and anxiety (0.435; 95% CI 0.141, 0.729; 3 RCTs). The review concluded that MBSR compared to waitlist is effective across a broad range of psychological outcomes but comparisons with other forms of treatment are less favorable. A second review addressed anxiety and mood symptoms across a range of populations but did not report a summary effect estimate for the 10 included RCTs and individual study results varied. The more general systematic review by the Campbell Collaboration on MBSR reported positive results for individual as well as a combined mental health outcome (SMD 0.53; 95% CI 0.46, 0.61; 26 RCTs), measures of personal development (0.50; 95% CI 0.35, 0.66; 12 RCTs), quality of life (0.57; 95% CI 0.17, 0.96; 4 RCTs), and mindfulness (0.70; 95% CI 0.05, 1.34; 7 RCTs).8 A review in cancer patients, described in more detail below, reported a positive effect of MBSR on mental health (Cohen's d 0.37; 95% CI 0.10, 0.64; p<0.003, 4 RCTs).55
Three systematic reviews addressed mindfulness interventions in chronic illness; the largest included 18 RCTs. The largest (MBSR) review did not pool across studies and the statistical significance of individual studies was not reported.61 A systematic review in adults with a chronic medical disease (defined as conditions that involve some disability caused by irreversible pathological change or illnesses that cause enduring disability) reported SMD 0.32 (95% CI 0.13, 0.50; 3 RCTs) for psychological distress, 0.26 (95% CI 0.18, 0.34; 6 RCTs) for depression, and 0.47 (95% CI 011, 0.83; 4 RCTs) for anxiety comparing MBSR to waitlist and support groups.25 The review concluded that MBSR has small effects on depression, anxiety, and psychological distress in people with chronic somatic diseases and speculated that integrating MBSR in behavioral therapy may enhance the efficacy of mindfulness based interventions. A third MBSR review found mixed results in individual studies and did not report an estimate across all studies.
We identified 8 systematic reviews focusing specifically on depression and the largest included 14 RCTs. The largest review addressed depressive symptoms in people with mental disorders treated with MBCT (12 RCTs), MBSR (1 RCT) or dialectical behavioral therapy with mindfulness training (1 RCT) and found a positive pooled effect (SMD 0.39; 95% CI 0.23, 0.55; p<0.001; 14 RCTs) either alone or in combination with usual care or medication, primarily compared to treatment as usual.49 The review concluded that mindfulness-based interventions are efficacious for alleviating depressive symptoms in adults with metal disorders and suggested the interventions could be used in conjunction with other treatments in clinical settings. A review on MBCT based on the manual by Segal et al tailored for depression in recurrent major depressive disorder found a significantly reduced risk of relapse/recurrence with a risk ratio (RR) of 0.66 (95% CI 0.53, 0.82; 5 RCTs) compared to treatment as usual or placebo controls.64 MBCT did not show a statistically significant difference compared to maintenance antidepressant medication across 2 RCTs. The authors concluded that MBCT is an effective intervention for relapse prevention in patients with recurrent major depressive disorder in remission, at least for patients with 3 or more previous episodes. A review on cognitive behavioral group therapy included MBCT RCTs; individual study results varied and no pooled was reported. A systematic review included 2 MBCT RCTs (both statistically significantly positive compared to treatment as usual only / no add-on MBCT therapy) but the authors concluded that because of the nature of the control groups the findings cannot be attributed to MBCT-specific effects.7 The Canadian Network for Mood and Anxiety Treatments Clinical Guidelines for the management of major depressive disorder in adults concluded that MBCT does not yet have significant evidence as acute treatment but considers it a second-line treatment for the maintenance phase of major depressive disorder in adults.63 Three additional reviews on depression did not report between group effects or did not find any relevant RCT for the specific review question. The Campbell Collaboration review reported a pooled effect of MBSR of SMD 0.54 (95% CI 0.35, 0.74; 9 RCTs) compared to waitlist or treatment as usual for the outcome depression.8 As shown, the AHRQ report on mindfulness meditation programs reported positive effects for depression (SMD 0.30; 95% CI 0.00, 0.59; at 8 weeks; 0.23; 95% CI 0.05, 0.42 at 3–6 months; 10 RCTs total).43 An MBSR-specific review reported a positive effect on depression (SMD 0.512; 95% CI 0.164, 0.861; 5 RCTs).20 Furthermore, reviews on cancer patients and survivors,65 chronic illness,25 somatization disorders,51 anxiety,77 and two reviews on mental illness33,41 also reported statistically significant pooled effects for the outcome depression.
Three systematic reviews addressed the role of mindfulness-based interventions in substance use treatment and the largest included 14 RCTs. Results of studies included in the largest review varied and no treatment estimate across all RCTs was reported.34 Two additional reviews also did not provide summary treatment estimates and results varied across studies and across outcomes. Three systematic reviews addressed psychological distress and the largest included 13 RCTs. The largest review evaluated bio-psychological training programs for the self-management of emotional stress for military personnel; the results of MBSR varied across studies or were not described in detail and the summary treatment estimate is not known.37 Two further reviews did not report pooled effects compared to a control group for RCTs and individual study results varied. A review on psychological outcomes reported positive results for the outcome distress (0.547; 95% CI 0.193, 0.901) but included only 6 MBSR RCTs.20 As reported, the chronic illness review reported positive effects on psychological distress (SMD 0.32; 95% CI 0.13, 0.50) but included only 3 relevant RCTs.25 The Campbell Collaboration and the AHRQ report on mindfulness meditation pooled the outcomes stress and distress and did not provide separate analyses for psychological distress8,43
One systematic review addressed somatization disorders and included 13 RCTs in patients with a diagnosis of fibromyalgia, chronic fatigue syndrome, irritable bowel syndrome, and nonspecified somatization disorder.51 The review reported positive effects for mindfulness-based therapies for the primary outcome symptom severity (SMD -0.40; 95% CI -0.54, -0.26; 10 RCTs) compared to waitlist or support group. Positive effects were also reported for the outcomes pain (-0.21; 95% CI -0.38, -0.03; 7 RCTs), quality of life (0.39; 95% CI 0.19, 0.59; 5RCTs), and depression (-0.23; 95% CI -0.40, -0.07; 8 RCTs), but not for anxiety. Stratified by mindfulness intervention, only MBSR and MBCT pooled results were statistically significant, but not eclectic/unspecified mindfulness-based therapy interventions. The authors concluded that preliminary evidence suggests that mindfulness-based therapies may be effective in treating at least some aspects of somatization disorders but there is a need for further research. We identified 3 systematic reviews on mental illness and the largest review included 12 RCTs. The largest review investigated MBCT in patients suffering from psychiatric disorders and reported a favorable effect of MBCT plus treatment as usual for the primary review outcome relapse prevention of major depression (odds ratio (OR) 0.36; 95% CI 0.19, 0.48, p<0.0003; 4 RCTs) compared to treatment as usual alone.33 Results for anxiety varied and were not pooled across studies. A further review also found positive pooled results for the relapse rate of patients with 3 or more previous episodes of depression at one year followup (RR 0.61; 95% CI 0.48, 0.79; 5 RCTs), depression measured with HAM-D (weighted mean difference WMD -2.46; 95% CI -4.36, -0.56; 3 RCTs at 1-year followup; WMD -10.39; 95% CI -15.66, -5.12; 2 RCTs post-intervention), depression measures with Beck depression inventory (WMD -10.39; 95% CI -15.66, -5.12; 2 RCTs at 1-year followup; WMD -7.33; 95% CI -12.12, -2.54; 6 RCTs post-intervention), and anxiety (different scales) at post-intervention (SMD -2.42; 95% CI -0.74, -0.09; 2 RCTs) comparing MBCT plus treatment as usual to treatment as usual alone, or MBCT plus support to discontinue or reduce antidepressants to maintenance antidepressants.41 The review concluded that MBCT is an effective intervention for patients with 3 or more previous episodes of major depression. A review on mindfulness-based treatment in people with severe mental illness did not find any RCTs.
Areas with a Smaller Research Base
Fewer research studies (ie, fewer than 10 RCTs identified in existing systematic reviews) are available for a large number of clinical indications and outcomes.
We identified one review specific to the effect of mindfulness-based therapy on anxiety and depression in adult cancer patients (cancer-depression/anxiety) and survivors and it included 9 RCTs. The review reported positive effects for anxiety (SMD 0.37; 95% CI 0.24, 0.50; p<0.001; 9 RCTs), depression (0.44; 95% CI 0.24, 0.64; p<0.001; 9 RCTs), and mindfulness (0.39; 95% CI 0.20, 0.58; p<0.001; 5 RCTs) of MBSR conducted according to Kabat-Zinn or MBCT conducted according to Segal compared to waitlist or treatment as usual.65 The review concluded that there appears to be some positive evidence from relatively high-quality RCTs to support the use of mindfulness-based therapy for cancer patients and survivors with symptoms of anxiety and depression. In contrast, 11 systematic reviews addressed the role of mindfulness interventions in cancer care in general (cancer-general) and the largest review included 5 RCTs. The largest review did not provide separate analyses for RCTs or a description of individual studies.60 One review in cancer patients reported a positive effect of MBSR for mental health outcomes (Cohen's d 0.37; 95% CI 0.10, 0.64; p<0.003, 4 RCTs) across a range of outcomes measures (distress, quality of life, mental health, sleep measures, sense of control, anxiety, depression, sense of coherence, mood) but not for physical health (measured through SF-36, symptoms of stress inventory physical health components).55 One review on complementary and alternative medicine on quality of life of cancer survivors included 3 mindfulness intervention RCTs and reported positive results (SMD 0.32; 95% CI 0.06, 0.57; 2 RCTs) for breast cancer survivors at 6 months but the exact mindfulness intervention and comparator were not specified.73 The remaining 8 reviews did not provide summary effect estimates for RCTs, and did not report individual study results, or reported conflicting results across studies and outcomes.
Two systematic reviews addressed patients with mood disorders and the largest one included 8 RCTs. The largest review concentrated on pre-post changes, not effects relative to a control group.45 The second review did not report a summary estimate across studies, and individual study results varied or comparative effects to the control group were not stated. We identified 4 systematic review addressing stress and the largest one included 7 RCTs. The largest review, targeting stress management in healthy people, did not pool studies in a formal meta-analysis and the statistical significance of the individual study results was not reported.30 The other reviews specific to stress pooled RCT results with other study designs, or identified only one or no RCTs relevant for the particular review question. A review on psychological outcomes reported positive effects on stress (0.792; 0.371, 1.213; 4 RCTs) but the review was limited to MBSR interventions.20 The Campbell Collaboration review and the AHRQ report on meditation programs combined the outcome stress and distress.8,43
Five systematic reviews addressing pain were identified and the largest review included 7 RCTs. The largest review pooled across study designs and all included acceptance-based interventions.76 Other reviews that addressed pain specifically did not provide summary estimates and results of individual study reviews varied, or only one RCT was identified for the particular review question, which was not analyzed for effects compared to the control group. The AHRQ report on mindfulness meditation reported a positive pooled effect on pain (Cohen's d 0.33; 95% CI 0.03, 0.62; 4 RCTs) compared to non-specified active control groups but not across 4 control groups with a specific active control group such as massage or yoga. The report concluded that there is moderate evidence of improved pain associated with mindfulness interventions.43 The review on somatization disorders reported positive effects for the outcome pain (WMD -0.21; 95% CI -0.38, -0.03; 7 RCTs) compared to waitlist or support group51 while 2 reviews on fibromyalgia found no effects on pain across studies.24,52
One systematic review addressed treatments used to reduce rumination and/or worry and included 6 mindfulness RCTs. Results of individual studies evaluating MBSR, MBCT, mindfulness meditation, and mindful breathing RCTs varied and no overall treatment estimate was reported.67 A review on mindfulness training to improve cognitive functioning included 6 RCTs. Results of individual studies varied across studies, outcomes, and interventions.29
We identified 3 systematic reviews that specifically addressed anxiety and the largest one included 5 RCTs. The largest review reported a positive effect across RCTs for anxiety symptoms at post-treatment (SMD -0.83, 95% CI -1.62, -0.04) and for depression symptoms (-0.72; 95% CI -1.20, -0.24) in patients with a diagnosis of anxiety disorders receiving MBSR, MBCT, or Acceptance and Commitment Therapy with a distinct mindfulness component; control group details were not reported.77 The review concluded that mindfulness- and acceptance-based interventions are associated with robust and substantial reductions in symptoms of anxiety and comorbid depressive symptoms and more research is needed to determine the efficacy relative to current treatments of choice. A Cochrane review on meditation therapy for anxiety disorders included one mindfulness RCTs comparing the effects of a relaxation/mindfulness meditation intervention and Kundalini Yoga; no statistically significant differences in obsessive compulsive symptoms were found between groups.50 A review on anxiety in bipolar disorders included one MBCT RCT (statistically significant positive effects on anxiety scores reported). The Campbell Collaboration review reported a treatment effect of SMD 0.53 (95% CI 0.43, 0.63; 10 RCTs) for anxiety comparing MBSR and waitlist or treatment as usual.8 The AHRQ report on meditation programs reported a positive pooled effect on anxiety (SMD 0.38; 95% CI 0.12, 0.64 at 8 weeks; 0.22; 95% CI 0.02, 0.43 at 3-6 months) comparing mindfulness meditation programs to a control group matched in time and attention to the intervention group across a number of anxiety outcome measures. A MBSR review reported a positive pooled effect on anxiety (0.435; 95% CI 0.141, 0.729; 3 RCTs).20 As shown above, pooled positive effects were also reported in a review on chronic medical diseases comparing MBSR to waitlist and support groups25; a review on mental health comparing MBCT plus treatment as usual to treatment as usual alone or MBCT plus support to discontinue or reduce antidepressants to maintenance antidepressants41; and a review on cancer patients; but a review on somatization disorders did not find effects on anxiety associated with mindfulness-based interventions compared to waitlist or support group across 5 RCTs.51
Three systematic reviews evaluated treatments for fibromyalgia and the largest one included 4 RCTs. The largest review did not find statistically significant differences between MBSR and waitlist or usual care, or active control interventions, for quality of life or pain (number of studies per comparison not reported).52 A review on cognitive behavioral therapy approaches included 3 mindfulness RCTs and reported no statistically significant difference across 2 RCTs for the outcome pain at post-treatment compared to waitlist or an attention control group.24 A further review included 2 mindfulness intervention RCTs but only one assessed pain or functional status.
One systematic review addressed psychosis and included 3 mindfulness RCTs. The review reported a positive effect of MBCT, mindfulness and metacognitive insight therapy, or mindfulness-based psychoeducation in patients with schizophrenia, schizophrenia spectrum, or outpatients with distressing voices (SMD 0.55; 95% CI 0.36, 0.75; 3 RCTs) compared to waitlist or usual care across all outcome measures (CORE, PSYRAT, BAVQ-r, SMQ, SMVQ, CGI-SCH, AAQ-II, SMQ, ITAQ, BPRS, SSQ-6, SLOF, rehospitalization).48 The authors concluded that mindfulness interventions are moderately effective in treating negative symptoms and can be useful adjunct to pharmacotherapy but more research is needed to identify the most effective elements of mindfulness interventions.
A review on mind-body practices on smoking cessation included 3 mindfulness RCTs. Individual studies evaluated mindfulness training and cue-exposure plus mindfulness; individual study results varied and no overall estimate specific to mindfulness-based interventions was reported.26 One review addressed the effects of mindfulness training on health care provider outcomes (provider-relevant) and included 3 RCTs. The statistical significance of training effects and/or the effects relative to a control group were not reported and no overall effect estimate was provided.10 We identified 2 systematic reviews on mindfulness-based interventions in multiple sclerosis and the larger one included 2 RCTs. The largest review did not find data for the primary outcome perceived stress and results for other outcomes were not reported in comparison to control group results.74 The other review did not include additional RCTs. Two systematic reviews evaluated mindfulness interventions in stroke care and both included (the same) one RCT. Both reviews did not report the effects of the mindfulness intervention relative to the effects of the control group.53,54 One systematic review evaluated mind-body practices for posttraumatic stress disorder (PTSD) and included one mindfulness intervention RCT. The RCT in cancer patients that assessed posttraumatic stress symptoms found no significant differences between intervention and control group in assessed outcomes, apart from in the outcome mindfulness, and continued meditation was associated with a reduction in avoidance symptoms.11 One review evaluated mindfulness and other Buddhist-derived interventions in correctional settings (correctional care) and included one RCT. The review reported a significant increase in negative outcome expectancies associated with a mindfulness-based relapse prevention program compared to a substance abuse educational program, but the effects on the other outcomes (depression and refusal self-efficacy) were not reported in comparison to a control group.19 One systematic review addressed complementary medicine, self-help, and lifestyle interventions for obsessive compulsive disorder (OCD) and the OCD spectrum and included one mindfulness intervention RCT. The review reported that the small RCT found a significant reduction in OCD symptom complaints with a large effect size in favor of a mindfulness training intervention compared to waitlist but stated that effects of other outcome measures (“letting go,” rumination) were not clearly reported.70
We identified systematic reviews on patients' experiences, eating disorders, intellectual disability, sleep disturbance, and hot flashes that systematically searched for mindfulness intervention but did not find any relevant RCTs.
Most promising areas
The most consistent effect was shown for the outcome depression compared to treatment as usual or waitlist. All reviews that reported a pooled analysis showed a positive effect.7,8,25,33,41,43,49,51,63-65,77
Positive effects were also shown for an overall effect on health and on psychological variables, but the analysis was limited to MBSR compared to passive control groups.8 Positive effects compared to waitlist and support groups were shown in the area of chronic illness but reviews only included MBSR studies and only considered the outcomes anxiety, depression, and psychological distress.25 Positive results were also found for somatization disorders analyzing symptom severity compared to waitlist or support group; however, stratified by intervention, only MBSR and MBCT pooled results were statistically significant, not eclectic/unspecific mindfulness-based therapies.51 Mental illness showed positive effects compared to treatment as usual alone, but reviews analyzed only MBCT studies and most data were available for the outcome depression.33
Positive effects were shown for MBSR or MBCT compared to waitlist or treatment as usual for the outcomes depression and anxiety of cancer patients or survivors but fewer than 10 RCTs were available.65 The comprehensive AHRQ report on meditation practices concluded that there is moderate evidence of improved pain associated with mindfulness interventions; not all reviews reported statistically significant positive effects for the outcome pain, and reviews identified fewer than 10 relevant RCTs. Although several reviews reported effects on anxiety compared to passive control, only a limited number of original studies (5 RCTs) was available and estimates of the size of the effect varied widely across reviews.8,25,41,43,50,51,77 Another area with limited research (3 RCTs) was psychosis treatment, which identified a review that reported overall positive effects across a variety of mindfulness-based interventions compared to waitlist or usual care, but the authors' conclusions were limited to negative, not positive, psychosis symptoms.48
VA priority areas
PTSD
As shown, we identified one systematic review that systematically searched for and evaluated effects of mindfulness-based interventions on PTSD.11 The review included 16 randomized and non-randomized studies evaluating a variety of mind-body practices, including studies in Veterans, and concluded that mind-body practices are increasingly used in the treatment of PTSD and are associated with positive impacts on stress-induced illnesses such as depression and PTSD in most studies. The review included one explicit mindfulness intervention RCT88 that found no differences between intervention and control group in symptoms of stress in 71 cancer patients but an association with continued meditation and a reduction in avoidance symptoms. The PTSD RCT reported that no adverse events or side effects were reported. The review discussed the safety of the interventions but did not report on adverse events in individual studies.
An additional literature search identified 4 PTSD-relevant RCTs indexed in PubMed. One RCT assessed acceptability, not patient health outcomes or adverse events; it concluded that implementing a manualized protocol is feasible in female Veterans and interviews showed positive responses.89 A pilot RCT assessed PTSD symptoms in Veterans with self-reported sleep disturbance and found a significant reduction associated with a mind-body bridging program for sleep management that was designed to increase mindfulness; adverse events were not assessed.90 A 16-session mindfulness-based stretching and deep breathing exercise intervention for nurses investigated effects on subclinical features of PTSD and found superior outcomes compared to no intervention; the presence or absence of adverse events were not reported.91 One RCT assessed the effect of MBSR plus treatment as usual compared to treatment as usual alone in 47 Veterans with PTSD.92 MBSR classes followed the original 8-week format and were taught by experienced instructors in groups of 20 to 30 male and female participants. Intention to treat analyses found improved but not statistically significant different scores comparing MBSR and treatment as usual alone. A post-hoc power analysis indicated more than 4 times as many participants are needed to demonstrate statistically significant effects. No participants withdrew due to worsening of PTSD symptoms or other difficulties with the intervention.
Stress
The mindfulness literature includes reviews on stress and on distress, and some reviews combined the outcomes in a stress/distress analysis. The majority of reviews did not define these outcome categories and a large variety of individual measures was included in the analyses, including Global Severity Index of the Symptom Checklist 90 Revised (SCL-90), Psychological Distress subscale of the SCL-90, Brief Symptom Inventory, Perceived Stress Scale, State-Trait Anxiety Inventory, Anxiety scale of the Profile of Mood States, and Differential Stress Inventory. As outlined, results on distress were not described in detail, varied across studies, or were clinical condition-specific, summarizing only a fraction of all relevant studies. Several systematic reviews have addressed the outcome stress in healthy people; however, study effects were not pooled in a formal meta-analysis, or identified only one study relevant to the particular review question.
The AHRQ report on meditation programs for psychological stress and wellbeing reported on the combined outcome stress/distress. The report differentiated unspecific active control and specific control interventions (eg, yoga). The report stated that 8 RCTs with unspecific active control groups were identified; however, only 6 could be pooled in a meta-analysis, excluding the RCT with the lowest risk of bias while one large RCT with a high risk of bias dominated the analysis. Hence no pooled result was reported. Compared to specific control interventions, mindfulness-based approaches were not statistically significantly different from control. The authors reported low strength of evidence of improved stress/distress in mindfulness meditation programs.3,43 The Campbell Collaboration combined the outcome stress and distress and the analysis included 20 RCTs, all evaluating MBSR. The review reported a positive effect for the combined outcome (SMD 0.56; 95% CI 0.44, 0.67) comparing MBSR and waitlist or treatment as usual.8 No information was given on which specific measures were combined in this analysis. A MBSR review based on 17 studies in a variety of clinical and non-clinical samples reported positive results for the outcome distress measured with the General Severity Index of the SCL-90 (SMD 0.547; 95% CI 0.193, 0.901; 6 RCTs) and stress measured as Symptoms of Stress Inventory or Perceived Stress Scale scores, or laboratory tests of stress hormones and other biological markers of stress (0.792; 95% CI 0.371, 1.1213; 4 RCTs).20 The review specified that the average length of MBSR class sessions was 120 minutes (standard deviation (SD) 38.24), the average number of sessions was 7 (SD 1.22), 88% of studies referred to meditation or breath awareness as part of the intervention, 88% included yoga or body movement, 82% homework, 71% body scan meditation, 65% specified a didactic training element, and 35% included a day-long retreat, but these numbers refer to all included studies, and are not limited to those reporting on stress or distress. A review in adults with a chronic medical disease reported SMD 0.32 (95% CI 0.13, 0.50; 3 RCTs) for psychological distress for MBSR but the comparator was not specified.25
Only one review out of 3 on emotional or psychological distress addressed adverse events, and the review did not report individual events reported in included studies but stated that there are very few to no adverse effects associated with the evaluated self-management skill programs when properly learned and practiced.37 Only one out of 4 reviews on the outcome stress addressed adverse events and that one only reported it for one included study (no reported adverse effects of the intervention).18 Safety was a key question in the AHRQ report on meditation practices that addressed the outcome category stress/distress. The report stated that few RCTs reported on potential harms of meditation programs. Of 9 RCTs that reported on harms, none reported any harms of the intervention. One trial specified that the researchers looked for toxicities of meditation to hematologic, renal, and liver markers and found none. The remaining 8 trials did not specify the type of adverse event they were looking for, 7 reported that they found no significant adverse events, while one did not comment on the encountered adverse events. The remaining 32 RCTs did not report whether they monitored for adverse events.3 The Campbell Collaboration review that addressed the area stress/distress stated that no explicit reporting on possible adverse effects was provided.8
Judging from a scoping search, more than 35 mindfulness-based intervention RCTs have been published after the completion of the literature search of the most comprehensive review, the AHRQ report on meditation interventions (updated for a journal publication in November 2012). These new RCTs report on the outcome stress or psychological distress, or describe an intervention that is explicitly applied to reduce stress.91-127 Individual study results varied and it is unclear which studies would meet inclusion criteria of the report, and whether the conclusion of low strength of evidence for improved stress/distress continues to be correct in a reanalysis.
Depression
Judging from existing systematic reviews, the most consistent effect of mindfulness-based interventions, including MBSR designed for stress reduction, was not found for the outcome “stress” but for the outcome “depression.” The outcome has received substantial research attention and all reviews that pooled across individual studies found positive effects of mindfulness-based interventions compared to passive control groups. This effect was not limited to MBSR or MBCT: positive effects were shown across all included interventions. However, a large number of existing studies had used these 2 more formalized programs.
Estimates of the size of the treatment effect varied across reviews, ranging from Cohen's d 0.23,43 Hedges' g 0.23,51 Hedges' g 0.26,61 Cohen's d 0.30,43 Cohen's d 0.39,49 Hedges' g 0.44 in cancer patients,65 Cohen's d 0.51,20 Hedges' g 0.54,8 to Hedges' g 0.72,77 indicating a small to medium effect. WMD estimates for common depression measures ranged from -2.46 (HAM-D, 1 year post-intervention), 41 -4.31 (HAM-D post-intervention),41 -7.33 (BDI post-intervention),41 and -10.3941 (BDI, 1 year post-intervention). RR 0.6664 and 0.6141 were estimated for the dichotomous outcome relapse/recurrence and one study reported OR 0.36 favoring the mindfulness-based intervention.33 Included reviews evaluated effects on the outcome depression in a variety of populations ranging from patients with recurrent major depressive disorder39,64 or a history of depression7 to a range of clinical indications not limited to depression.8,33,43
The majority of studies included in systematic reviews estimated the effect of the intervention compared to a passive control group (some reviews only searched for this type of study). A common comparator in reviewed studies was waitlist or treatment as usual. Some reviews suggested that mindfulness interventions could be used in conjunction with other treatments.49 However, in many systematic reviews it was not clearly stated whether all participants in the RCT had received treatment as usual, with the difference between the groups being that one received a mindfulness intervention while the other did not (mindfulness intervention as add-on treatment). Several reviews, including depression-specific reviews, stated that the existing studies are not designed to determine whether the mindfulness component is responsible for the effectiveness of the interventions (in particular in MBCT interventions because MBCT was not compared to traditional CBT), or whether there are mindfulness-based-specific intervention effects given that the intervention group was compared to a passive control group.7,13 Pooled comparative effectiveness effects were reported in 2 reviews. One review concluded that MBCT was at least as effective as maintenance antidepressant medication because the pooled result showed no statistically significant difference between groups in a pooled analysis (RR 0.80; 95% CI 0.60, 1.08; favoring mindfulness; p=0.15; 2 RCTs); both individual included studies did not report a statistical power analysis.64 The AHRQ report on meditation interventions differentiated specific and non-specific active control interventions and compared to specific active controls; a combination of the interventions MBSR, MBCT, mindfulness meditation, and other mindfulness intervention did not show statistically significant differences compared to spirituality, relaxation, pain control, Vinyasa yoga, cognitive behavioral group therapy, antidepressants, or aerobic exercise control groups. Results in individual studies varied by comparators and showed no statistically effect between groups or favored the non-mindfulness-based intervention. However, a positive treatment effect was shown compared to unspecific active control groups that were at least matched in time and attention to the intervention group to control for the nonspecific effects of time, attention, and expectation (SMD 0.30; 95% CI -0.00, 0.59; at 8 weeks; SMD 0.23; 95% CI 0.05, 0.42 at 3–6 months; 10 RCTs total).3
Few reviews included a detailed description of the intervention. The AHRQ report that reported effect size estimates of 0.23 to 0.30 for depression included only structured meditation programs (defined as systematic or protocolized meditation programs that follow predetermined curricula) consisting of at least 4 hours of training with instructions to practice outside the training session.43 A review on psychiatric disorders that reported a positive OR of depression relapse in favor of MBCT reported that in 5 out of the 12 included studies the instructor was one of the founders of MBCT, was supervised by one of the founders, or had been trained by one of the founders of MBCT.33 The review on anxiety and depression effects in patients with cancer specified that all effects that reported a positive effect on anxiety and depression specified that interventions were based on MBSR conducted according to the program by Kabat-Zinn and MBCT according to Segal et al.65 A review reporting a positive effect on relapse prevention specified that included interventions were limited to MBCT based on the manual by Segal et al tailored for depression in recurrent major depressive disorder.64 The interventions in the studies contributing to a positive result on depression in anxiety disorders were all based on a group format.77 As outlined, even reviews limited to a specific program such as MBSR indicated variation in the intervention implementation, and information was summarized across all included studies and characteristics of studies reporting on stress or depression.20 A review on depressive symptoms in mental health reported a mean number of sessions of 10 (SD 3.3), total intervention hours mean 21 (SD 5.36), session duration mean 124 minutes (SD 25.8), and different therapist background (eg, CBT therapist) across interventions but data were not reported separately for mindfulness interventions.49 Information on the intervention components, implementation characteristics, and the training of the mindfulness instructor was rarely documented in the included reviews, independent from the clinical area.
Of 7 depression-specific reviews that included mindfulness intervention RCTs, 3 commented on adverse events. One review that included 14 RCTs reported that adverse effects were not addressed in any of the included studies.49 A second review stated that adverse events were not summarized because the data were sparse, inconsistent, and uninformative.84 A third review did not assess adverse events but stated that MBSR is a psychological alternative with no adverse medical side-effects.64 We did not identify summary estimates on suicide and suicide ideation. Reviews on depression,49 mental illness,41 and mood disorders6 explicitly included RCTs in patients with depression and suicide ideation; however patient groups were, in most cases, explicitly described as in recovery at the time of the trial, and results on the outcome were not reported. The mood disorder review suggested, based on an individual case study, that MBCT possibly decreases cognitive vulnerability to suicidality.6
A scoping search indicated that since the AHRQ report on meditation programs, at least 17 new RCTs have been published that addressed the outcome “depression,” including comparative effectiveness studies comparing the effects of mindfulness interventions to other treatments.92,96,97,105,107,108,114,121,127-135 Without careful assessment it is not possible to establish whether studies may challenge the summary of moderate evidence for improved depression3; however, only 6 RCTs included more than 100 participants and none included more than 350.97,107,114,119,121,130,135 The RCTs evaluated very different populations and study results varied across studies.
Wellness
Some included systematic reviews addressed the effects of mindfulness-based interventions in healthy adults, not clinical samples with a medical diagnosis. A review on psychological variables included 17 RCTs and reported a small effect (r 22; 5 RCTs) for mindfulness meditation, and r 0.29 (12 RCTs) for MBSR in nonclinical samples.9 The review's conclusion focused on the difference seen for MBSR and mindfulness meditation across all included studies, not RCTs specifically, and did not report recommendations for practice. Reviews in workplace setting interventions, 21 stress management in healthy people,30 stress-management programs for medical students,17,18 and stress reduction in university students,16 did not provide between-group meta-analytic effect estimates.
One systematic review provided a subgroup analysis for nonclinical / community samples and estimated Cohen's d 0.664 (95% CI 0.37, 0.96; 6 RCTs) as the effect of MBSR across a variety of psychological outcomes compared to waitlist control.20 As outlined previously, intervention characteristics were summarized across all 17 included MBSR studies, not separately for the nonclinical samples. The Campbell Collaboration review reported positive effects for outcomes in the wellness domain (personal development 0.50; 95% CI 0.35, 0.66; 12 RCTs; quality of life 0.57; 95% CI 0.17, 0.96; 4 RCTs) but results were based on a combination of clinical and non-clinical samples.8
Adverse events were only addressed in 2 of the 8 systematic reviews. As discussed, one review reported for one study that there were no adverse events18; the Campbell Collaboration review noted that reports on adverse events were missing from all included studies.
New RCTs in healthy adult participants, published since the comprehensive review that included non-clinical samples (search end date March 2010),9 address cognitive-affective neural plasticity136; acute respiratory infection prevention137; online stress interventions120,121; loneliness138; worry139; pre-session centering for therapists140; emotional response to film clips141; repetitive thoughts142; emotional benefits in older adults129; spatial abilities143; cognitive rigidity144; stress during pregnancy93; job satisfaction145; telomerase activity146; experimentally induced pain109,147-149; attention150,151; postural balance152; subjective effects and cognitive costs153; intrinsic brain connectivity154; body image155; weight loss156; experimental behavior modification157; stimulus over-selectivity158; provider burnout105; self-compassion159; experimentally induced stress103; distressed personality traits102; caregiver support96,160; blood pressure161; distress in breast-feeding mothers101; emotion regulation processes162; experimentally induced neurogenic inflammation100; trait mindfulness163; stress in the workplace99,164; stress in medical students165; childbirth and labor166; and physician wellbeing.127 The largest trial (1,222 healthy nulliparous women) identified in the scoping search found no between-group differences in use of epidural analgesia, self-reported pain measures duration of childbirth, and other birth outcomes comparing self-hypnosis, relaxation and mindfulness training, and usual care.166
FUTURE RESEARCH
Systematic reviews in patients' experiences, sleep disturbance, hot flashes, eating disorders, and intellectual disability specifically searched for mindfulness intervention studies, but no RCTs (ie, high level of evidence research studies) were identified. Most evidence is available for comparisons of mindfulness interventions and passive comparators; information on comparisons to active control groups and comparative effectiveness research is currently very limited. The evidence map has identified a number of areas with unclear evidence. Future systematic reviews may provide more definitive answers. In some cases, the scope of the review might have to be reduced to concentrate on specific outcomes or clinical indications, and the effect of MBSR, MBCT, and other mindfulness-based interventions may need to be evaluated individually.
Ongoing Research
A protocol for a Cochrane review on mindfulness-based ‘third wave’ cognitive and behavioral therapies (including MBCT, Acceptance and Commitment Therapy, Compassionate Mind Training, and Dialectical Behavior Therapy) for depression was published in 2010 and was updated in 2012.167 Unpublished systematic reviews registered in PROSPERO that specifically target mindfulness-based intervention studies address MBSR in breast cancer care (CRD42014009409), mindfulness-based approaches to treat pathological gambling (CRD42014010748), mindfulness meditation for overeating and weight loss (CRD42013004293), mindfulness in primary care (CRD42013004133), and MBCT and MBSR for depression and vascular disease (CRD42013003852).
- RESULTS - Evidence Map of MindfulnessRESULTS - Evidence Map of Mindfulness
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