Background
An increasing number of mindfulness-based stress reduction (MBSR) studies are being conducted with nonclinical populations, but very little is known about their effectiveness.
Objective
To evaluate the efficacy, mechanisms of actions, and moderators of MBSR for nonclinical populations.
Data sources
A systematic review of studies published in English journals in Medline, CINAHL or Alt HealthWatch from the first available date until September 19, 2014.
Study selection
Any quantitative study that used MBSR as an intervention, that was conducted with healthy adults, and that investigated stress or anxiety.
Results
A total of 29 studies (n = 2668) were included. Effect-size estimates suggested that MBSR is moderately effective in pre–post analyses (n = 26; Hedge's g = .55; 95% CI [.44, .66], p < .00001) and in between group analyses (n = 18; Hedge's g = .53; 95% CI [.41, .64], p < .00001). The obtained results were maintained at an average of 19 weeks of follow-up. Results suggested large effects on stress, moderate effects on anxiety, depression, distress, and quality of life, and small effects on burnout. When combined, changes in mindfulness and compassion measures correlated with changes in clinical measures at post-treatment and at follow-up. However, heterogeneity was high, probably due to differences in the study design, the implemented protocol, and the assessed outcomes.
Conclusions
MBSR is moderately effective in reducing stress, depression, anxiety and distress and in ameliorating the quality of life of healthy individuals; however, more research is warranted to identify the most effective elements of MBSR.
Stress is prevalent in modern society and has become a significant global health problem [1] and [2]. Research suggests that high levels of stress can negatively affect both physical and mental health and are found to be associated with autoimmune diseases [3], migraines [4], obesity [5], muscle tension and backache [6], high cholesterol [7], coronary heart disease [8], hypertension [9], and stroke [10].
In the last decade, interest in research investigating mindfulness-based interventions has increased substantially [11]. Even though a consensus about an unequivocal operational definition of mindfulness is lacking so far [12] and [13], one of most commonly employed definitions of mindfulness was provided by Jon Kabat-Zinn who suggests that mindfulness could be described as a moment to moment awareness that is cultivated by purposefully paying attention to the present experience, with a non-judgmental attitude [14]. Interventions utilizing mindfulness techniques have shown efficacy for treating a variety of mental disorders and in coping with physical or medical conditions, including, among others, chronic pain [15], fatigue [16], stress [17] and [18], cancer [19], heart disease [20], type 2 diabetes [21], psoriasis [22], and insomnia [23].
Mindfulness-based stress reduction (MBSR) [24] is a well-established mindfulness training that has shown to reduce stress, depression, and anxiety [25] and [26]. MBSR teaches individuals to observe situations and thoughts in a nonjudgmental, nonreactive, and accepting manner. MBSR provides training in formal mindfulness practices, including body scan, sitting meditation, and yoga. MBSR seeks to change the individual's relationship with stressful thoughts and events by decreasing emotional reactivity and enhancing cognitive appraisal [27]. The standard MBSR curriculum is conducted in an 8-week structured group format, which includes weekly 2.5-hour group sessions in addition to a 6-hour daylong retreat.
Although initially developed for chronic pain, MBSR has reported positive results among an array of clinical and nonclinical populations, including cancer, health care professionals, continuing education students, and college undergraduates [28], [29] and [30]. Chiesa et al. [28] were the first to systematically investigate the usefulness of MBSR in healthy individuals. They concluded that MBSR provided a significant nonspecific moderate to large effect on the reduction of stress in comparison with no-treatment controls. However, there were significant methodological limitations and only 10 studies were included in the analysis. Eberth and Sedlmeier [30] conducted a meta-analysis of 38 controlled studies on the effects of mindfulness meditation on psychological well-being among a nonclinical population. Among the 38 studies, 17 used MBSR, the results suggested moderate effects in reducing stress and negative emotions and in increasing well-being. However, the meta-analysis included only studies that were published before March 2010, had some methodological limitations (e.g., it did not implement PRISMA criteria and it did not include a quality measure), failed to determine moderators of the observed effects, did not investigate the role of mindfulness in the effectiveness of the interventions, and did not investigate long-term effects of MBSR.
A more recent qualitative systematic review examined the effects of MBSR on stress management in nonclinical populations in 17 trials dating between January 2009 and 2014 [29]. The outcomes suggested positive effects on both psychological and physiological measures without quantifying these effects. Overall, the current state of the literature suggests the need for a more systematic quantifiable summarization of the effects, mechanisms of actions, and moderators of MBSR for nonclinical populations. Therefore, we conducted a comprehensive effect-size analysis with the following objectives: (1) to quantify the effect size of MBSR for psychological variables (i.e., anxiety, depression, stress, distress, and burnout) in healthy individuals; (2) to investigate and quantify the role of mindfulness in MBSR; and (3) to explore moderator variables.
