Table 1.
Summary of studies included in the review.
| First Author and Year | Studies Included | Target Population | Implemented Intervention | Comparison Group | Effect Size | Main Results |
|---|---|---|---|---|---|---|
| [26] | 21 uncontrolled and controlled studies, but only two were based on anxiety disorder | Anxiety clinical sample | MBSR | None | d = 0.70 | Kabat-Zinn et al. [27] examined patients with generalized anxiety and panic disorders and found significant improvements (also at 3-month follow-up). Miller, Fletcher, and Kabat-Zinn [28] reported a 3-year follow-up of the same participants and results were maintained. |
| [29] | 39 uncontrolled and controlled studies | Anxiety clinical sample | MBSR or MBCT | None, TAU, educational social support with relaxation, anxiety education program, waiting list | For anxiety disorders, ES estimates suggest that mindfulness-based therapy was moderately effective for improving anxiety (Hedges’ g = 0.63; 95% CI = 0.47 to 0.87) from pre- to post-treatment in the overall sample | The uncontrolled pre-post ES estimates were in the moderate range for reducing anxiety symptoms. MBT in patients with anxiety disorders was associated with a large ES. |
| [30] | 19 controlled and uncontrolled trials | Individuals with clinical levels of anxiety | Multi-component acceptance-based interventions (CBT) | Stand-alone mindfulness | Between groups Hedges’ g = −0.83; 95% CI = −1.62 to −0.04 | MBIs are associated with robust and substantial reductions in symptoms of anxiety. No significant differences emerged between stand-alone mindfulness interventions and multi-component treatment packages. |
| [31] | 11 randomized controlled trials | Patients diagnosed with anxiety disorders | MBCT | TAU | The average degree of anxiety decreased compared to TAU (Hedges’ g = −0.42; 95% CI = −0.74 to −0.09) | Anxiety obtained significant but unstable results in sensitivity analyses comparing additive MBCT against usual treatment. |
| [23] | 209 waiting list-controlled studies but only 32 focused on anxiety | Medical conditions and non-clinical population with elevated initial anxiety | MBI | Pre-post studies, waiting list controlled and psycho-educational interventions, supportive therapies, relaxation and imagery/suppression technique | The SMD was large (10 studies pre-post) for anxiety studies (Hedges’ g = 0.89; 95% CI = 0.71 to 1.08) and for 4 waitlist-controlled studies (Hedges’ g = 0.96 (95% CI = 0.67 to 1.24) | MBT is moderately effective in pre-post comparisons, in comparisons with waitlist controls and when compared with other active treatments, including other psychological treatments. MBT did not differ from traditional CBT or behavioral therapies or pharmacological treatment. MBT was associated with the largest mean ES for anxiety. |
| [13] | 12 randomized controlled trials; 9 included a measure of anxiety symptoms | Full diagnostic criteria for anxiety | MBCT, MBSR and person-based cognitive therapy | Active control conditions (psychoeducation) and inactive control conditions (waiting list, aerobic exercise) | There was a non-significant post-MBI between-group difference in anxiety symptom severity (Hedges’ g = −0.52; 95% CI = −1.11 to 0.06). MBCT vs. inactive control (Hedges’ g = −1.03; 95% CI = −0.40 to −1.66). MBCT vs. active control (Hedges’ g = 0.03; 95% CI = 0.54 to −0.48). | There were no significant post-intervention between-group benefits of MBIs relative to inactive control conditions on anxiety symptom severity nor was there was an active control. |
| [32] | 8 randomized and non-randomized clinical trials | Anxiety clinical sample | ACT, MBCT, MBSR | Waiting list, TAU, psychoeducation, CBT, aerobic exercises, relaxation | It was suggested that psychological interventions based on mindfulness constitute an effective treatment for GAD (from d = 0.92 to d = 3.4), SP (from d = 0.41 to d = 0.78), and PTSD (d = 0.63) when used as adjuncts to pharmacological treatment | The interventions based on mindfulness constitute an effective treatment for GAD, SP, and PTSD, when used as adjuncts to pharmacological treatment. However, an ES that combines the significant differences obtained for each of the disorders is not provided. For the comparison between treatments based on mindfulness and other treatments for anxiety (CBT, applied relaxation, and aerobic exercise), it is suggested that the former is not superior to the latter in terms of efficacy. Both MBSR and MBCT seem highly efficient interventions. |
| [33] | 7 randomized controlled trials (RCTs) | Anxiety symptoms with a wide range of physical and psychological conditions | MCBT and ACT | Pre-post studies, control and active control groups | ES varied from not effective (Hedges’ g = 0.23) to large and positive (Hedges’ g = 1.90). The random effect model showed an overall moderate ES (Hedges’ g = 0.58; 95% CI = 0.27 to 0.88) of mindfulness-based CBT for anxiety symptoms among older adults | Effect-size estimates suggest that mindfulness-based CBT is moderately effective on anxiety symptoms in older adults (g = 0.58) |
| [34] | 15 RCTs, 11 comparisons on anxiety | Anxiety clinical sample | ACT, MBCT, MBSR, Internet-based Mindfulness treatment | Control group | Based on 11 comparisons, a significant, small ES was found for online MBIs on anxiety, with g = 0.22 (95% CI = 0.05 to 0.39, p = 0.010) and no outliers. After removal of low-quality studies from the analysis, the ES was virtually the same (g = 0.21, 95% CI = 0.03 to 0.40, p = 0.022). | A small but significant ES was found on anxiety. The online MBIs are not as effective as traditional face-to-face MBIs in reducing anxiety. |
| [21] | 142 randomized clinical trials (18 based on anxiety disorders) | Anxiety clinical sample | MBI | No treatment, specific active control, evidence-based treatment | For anxiety, MBIs were equivalent to the comparison group (d = 0.15 (95% CI = −0.16 to 0.46) and were equivalent to EBTs (d = −0.18 (95% CI = −0.41 to 0.06) | Mindfulness-based interventions were equivalent to the comparison group and EBTs for anxiety |
| [35] | 9 randomized trials | Anxiety clinical sample | MBI | CBT (active control groups) | Between groups Cohen’s d = −0.02; 95% CI = −0.16 to 0.12 | No statistically or practically significant differences between mindfulness and cognitive behavioral intervention |
| [36] | 10 randomized controlled trials | Anxiety clinical sample | MBCT and MBSR | Control conditions, CBT | MBIs were superior to control interventions for internalizing (SE = 0.26; 95% CI = 0.64 to 0.12; p = 0.00) and distress (SE = 0.12; 95% CI = 0.7 to 0.21; p = 0.00), but not for fear symptoms (SE = 0.22; 95% CI = 0.45 to 0.4; p = 0.90). A significant difference that favor CBT over MBIs for the fear domain symptoms were found (SE = 0.1; 95% CI = 0.1 to 0.46; p = 0.00). No evidence for superiority of CBT over MBIs was found. | MBIs were superior to control interventions for internalizing and distress, but not for fear symptoms. CBT was superior to MBIs for fear symptoms but not for internalizing and distress. |
Notes: CBT = cognitive behavioral therapy; MBI = mindfulness-based interventions; MBCT = mindfulness-based cognitive therapy; MBSR = mindfulness-based stress reduction; CBGT = cognitive behavioral group therapy; SMD = standardized mean difference; TAU = treatment as usual; RCT = randomized controlled trial; CI = confidence interval; NA= not available; ES = effect size; ACT= acceptance and commitment therapy; GAD = generalized anxiety disorder; SP = social phobia; PTSD = posttraumatic stress disorder; EBT = Evidence-based treatment.