Experiences of prolonged psychosocial stress is currently not targeted by evidence-based programs in most public health sectors [
45]. The present RCT supported that the meditation-based program “Open and Calm” (OC) developed for this purpose decreased participants’ perceived stress, depressive symptoms, and sleep disturbances, and increased their self-reported mental health and quality of life significantly more than the Danish health sector’s treatment as usual (TAU) for otherwise healthy adults complaining about reduced daily functioning due to prolonged stress. Treatment effects were consistently sustained at 3 months follow-up and OC participants reported significantly better mental health than TAU controls at follow-up on all self-report scales (Table 1). According to well-established cut-offs, OC reduced the risk for depression due to poor quality of life (QOL; [
31]) and sleep disturbances (PSQI; [
15]). OC participants reported follow-up levels corresponding to Danish norms for perceived stress [
71], mental health [
5], and symptoms of depression [
63] (Fig.
2). Control participants showed heightened risk for depression and suboptimal mental health scores throughout the six months study period.
OC improved the included self-report parameters with similar or slightly larger effect sizes (mean self-report T
1-T
3d =1.10; mean self-report T
1-T
2d = 0.70; Table 1) than typically found in studies of healthy samples participating in courses based on mindfulness meditation or transcendental meditation, according to meta-analytic reviews ([
21]:
d = 0.74; [
34]:
d = 0.50; [
68]:
ds = 0.54–0.56). Similarly, the effect from baseline to 3-month follow-up of OC on Cohen’s perceived stress scale (PSS;
d = 1.30) was larger than a baseline-3-months follow-up analysis on PSS of public stress reduction workshops based on cognitive and/or behavioral therapy ([
53], mean
d = 0.91). Thus, OC seems promising compared with other stress reduction programs. However, the present findings, especially the physiological results, should be interpreted with caution due to the limited sample size compared to meta-analytic reviews. Further and larger OC studies are needed.
Physiological stress, in terms of cortisol secretion and HPA-axis dynamics, was also investigated. The primary analyses included all participants and did not show significant changes on any cortisol outcomes in any group (Additional file
4: Table S2). However, based on the potential exhaustion of HPA-axis dynamics after prolonged stress ([
6]) and associations between burnout and blunted CAR [
43,
54,
59,
67], our secondary analyses separated participants into two subgroups according to their baseline CAR (AUC
I) profile. The first subgroup included all participants with an initially present (non-blunted) CAR. Within this group, OC participants decreased significantly on the magnitude of cortisol secretion (AUC
G), and also significantly more than in non-blunted TAU controls, even after controlling for relevant covariates and baseline AUC
G levels. Decreasing circulating levels of cortisol may be important in restoring health and preventing negative consequences of prolonged stress, e.g., because it may prevent neural atrophy in frontal and hippocampal regions, improving top-down regulation of limbic systems, promoting stress resiliency [
19]. The stimulated HPA-axis output (AUC
I) also decreased significantly in OC participants with non-blunted baseline CAR (Additional file
5: Panel S2, a). This change may relate to improved stress resiliency, since HPA-axis reactivity has been associated with several risk factors for depression, including 5-HTTLPR genotype [
20]. In the present study, 5-HTTLPR genotype was unrelated to any treatment effects. This is contrary to one study indicating stronger physiological stress reduction effects in SS-carriers than SL-carriers in a student sample [
61]. More knowledge is needed on genetic effect moderators of stress reduction effects of meditation-based programs in different sample types. Effects of 5-HTTLPR may decrease with age ([
75]). In addition, CAR is not a direct measure of individuals’ reactivity to everyday stressors (but see [
20,
32]) and effects of 5-HTTLPR-genotype on reactions to stressful stimuli interact with environmental factors [
16]. AUC
I changes did not differ between OC and TAU. Thus, the main cortisol effect of OC was a reduction in the magnitude of cortisol secretion for participants with a non-blunted CAR at baseline. In addition, as we hypothesized, AUC
I increased significantly for OC participants with a blunted baseline CAR. This suggests that HPA-axis dynamics, i.e., HPA axis reactivity to stimulation (awakening), was re-established (Additional file
5: Panel S2, b). A renormalization of CAR potentially also influenced TAU controls, but we could not evaluate this AUC
I change statistically with only
n = 2 blunted TAU controls (Additional file
4: Table S2). Cortisol studies of meditation and stress reduction have produced mixed findings and lacked methodological rigor [
55], rendering the present analytic strategy potentially applicable to future studies of prolonged stress. HPA-axis reactivity (AUC
I) has been suggested as a potential marker of physiological reactivity to stressors, such as psychosocial stress [
32]. However, cortisol is complexly related with prolonged stress and further studies of HPA-axis dynamics, prolonged stress, and burnout are clearly needed [
25].
Visual perception
The threshold of conscious visual perception,
t0, improved significantly more in OC than in controls, also when adjusting for baseline. Further, larger
t0-improvements were associated with increased OC compliance. This corroborates the previously reported finding that the TVA
t0 parameter was specifically improved by meditation and not by physical stress reduction [
42]. Interestingly, the TVA-model [
12,
13] states that
t0 improvements may reflect stronger reliance on bottom-up-driven perception, rather than conscious recalibration of attentional weights. OC may therefore have improved the perceptual threshold because participants became less prone to consciously modulate visual attention. This aligns with the OC training in
relaxed and
receptive (“Open”) awareness of sensory information and a
non-intervening (“Calm”) conscious witnessing. As mentioned, these are essential elements for many meditative traditions. Correspondingly, the visual perceptual threshold was also improved by yoga [
8,
78] and mindfulness meditation [
42,
52]. Mindfulness has also improved the threshold for conscious registration of proprioceptive stimuli [
62] and the perceptual threshold in an auditory temporal discrimination task [
27]. As argued by recent theories, meditation may facilitate insight into personal states and promote objective perception in general through increased perceptual sensitivity within several sensory modalities, i.e., through a lowering of the stimulation needed for conscious registration [
4,
14]. Our findings support these proposals, but clearly more research on bottom-up perceptual effects of meditation is needed.
Experiences from the practical implementation
The Open and Calm program received a 94 % completion rate. GPs found it easy to use a simple, online referral system and maintaining the full screening at the program distributor (Copenhagen University Hospital) ensured similar inclusion procedures throughout. However, among 20 referring GPs, ten GPs referred only one—two patients each. GPs and psychiatrists are generally not accustomed to referring stressed, but otherwise healthy individuals to treatment [
57]. To achieve sustainability, we reiterate recommendations [
45] that mental health program distributors employ health workers specifically for sustaining recruitment through local health facilities.
The two intervention formats (individual/groups of
n = 8) yielded similar treatment effects (Additional file
2: Panel S1). This is important, since individual courses required 2.6 times more professional contact hours per participant. Workshops for even larger groups also reduced stress [
10,
53] and anxiety [
9]. A stepped care model [
26] may be recommendable, where less intensive or demanding group programs are offered as a first-line treatment, while smaller or individual courses are offered when deemed necessary. A less intensive (minimal contact) group OC intervention is currently investigated. In general, more systematic research is needed on public health intervention formats [
45]. The OC intervention differs from other programs mainly because it was specifically designed for public mental health promotion in a broad demographic group (A full intervention description can be supplied by request to the first author). OC was thus carried out in a health promotion clinic, not in e.g., hospital settings. OC prioritizes everyday words such as
Open and
Calm, rather than e.g.,
beginner’s mind,
non-judgment, or
mindfulness [
44]. Perhaps most importantly, OC teaches meditation as a definable strategy and not as a special state of mind (for a discussion of these contrasting approaches, see Shapiro & Walsh [
69]). OC finally emphasizes a body-psycho-social focus on promoting mental health, rather than a more narrow focus on meditation. Therefore, findings may not be generalizable to other types of meditation-based programs.
The dropout rate of only 6 % may be important. Dropout in meditation-based stress reduction programs typically ranges 15-30 % [
64]. Based on participant feedback, the most appreciated elements of the OC program were the meditative practices and the programme structure, repeating bodily, mental, and social themes. This, however, is speculative and should be clarified by qualitative studies. We speculate that the choice of conducting evening sessions also lowered the dropout rate, especially for employed OC group participants, enabling them to maintain a normal working week. Individual OC participants could flexibly book course sessions in expanded working hours (8 am–6 pm).
Limitations of the RCT include the need for studying longer time periods, such as a year. A longer study period would enable more direct health impact assessments [
49], such as measures of the occurrence of stress-related depression or days of stress-induced absence from work. An active control group would have improved the ability to detect OC-specific effects. However, an unrestricted TAU design allowed a comparison of OC with the current, unsystematic treatments offered for healthy adults dealing with prolonged stress. As another limitation, the paucity of significant associations between OC session attendance rates and outcome change scores should not be extrapolated to indicate that compliance with meditation is unimportant in OC or similar programs. The absence of evidence is not the evidence of absence – and several studies of short-term meditation programs did find that increased meditation compliance was related to larger treatment effects [
79]. The simple compliance measure of session attendance may have prevented us from detecting such associations. More detailed compliance measures are most likely necessary to illuminate the importance of compliance with different elements of such programs. Relatedly, our relatively low sample size, especially in the cortisol analyses, limits the statistical power to detect treatment effect moderators, so these secondary findings should also be interpreted cautiously.