The Relationship between Mindfulness, Psychological Flexibility, and Symptom Severity in Persons with Schizophrenia-Spectrum-Disorders – a Cross-Sectional Study

doi:10.21203/rs.3.rs-4313238/v1

The effectiveness of mindfulness-based interventions (MBIs) in enhancing mental well-being and reducing positive, negative, and depressive symptoms in schizophrenia spectrum disorders (SSD) has been demonstrated by a growing body of evidence. However, the underlying mechanisms of MBIs still need further examination. Psychological flexibility (PF), generally assessed by cognitive fusion, has been shown to be associated with clinical change in MBIs. This study used a cross-sectional design to investigate the interplay of mindfulness, PF, and symptom severity in SSD. In total, N = 94 individuals with SSD were included. Correlation and mediation analyses were performed using PROCESS analysis with positive, negative, and depressive symptom severity as outcome variables, measured by the Positive and Negative Syndrome Scale (PANSS) and the Depression Anxiety Stress Scale (DASS-21), respectively. Findings indicated that mindfulness was significantly negatively correlated with positive and depressive symptoms, as well as significantly positively related to PF. A significant mediating effect of PF was found for the relationship between mindfulness and negative as well as depressive symptoms. The current study supports previous research about PF as a possible mechanism of action in MBIs. Still, future research using longitudinal designs, more fine-grained analyses, and mixed-method approaches regarding assessment tools are warranted.

Biological sciences/Psychology

Health sciences/Diseases/Psychiatric disorders/Psychosis

Health sciences/Diseases/Psychiatric disorders/Schizophrenia

schizophrenia spectrum disorders

mindfulness

psychological flexibility

mediation

negative symptoms

depressive symptoms

Mindfulness, which has emerged as a promising approach for improving mental health in recent years, is the process of consciously experiencing the current state of one’s immediate body, mind, and environment without being distracted by inner thoughts, memories, fantasies, or strong emotions, as well as without evaluating these perceptions [1]. Mindfulness-based treatment approaches were found to be efficacious in the treatment of a variety of conditions such as chronic pain [2, 3], substance misuse [4], depressive symptoms [5] as well as anxiety and stress [6]. Concerns about negative effects of mindfulness practices for persons with schizophrenia spectrum disorders (SSD), which derived from reports about adverse events such as depersonalization, altered reality testing, or the appearance of previously repressed memories and conflicts occurring after highly intensive meditation practices [7], led to an initial hesitation in the development of the evidence base for its use for SSD relative to common mental disorders such as anxiety and depression [8]. Adaptions of mindfulness practices such as delivery in small groups, short durations, avoiding prolonged periods of silence, and using simple language made their implementation in clinical practices safe for persons with SSD [8]. Furthermore, accessibility to and cost-efficiency of treatment is improved by offering mindfulness-based interventions (MBIs), as these can successfully be delivered in group format to persons with SSD [9], in which they are even more effective in comparison to delivery in individual format [10].

Evidence from meta-analyses on the effectiveness of mindfulness- and acceptance-based interventions for improving symptom severity in SSD is promising but mixed [10–15]. Some meta-analyses [11, 12, 14, 15] report significant small effects on positive symptoms (Hedge’s g = 0.32–0.48), while others did not find these effects [10, 13]. Similarly, significant effects on negative symptoms (g = 0.24–0.75) were only found by Hodann-Caudevilla et al. (2020), Jansen et al. (2020), and Khoury et al. (2013) [12–14], and not by Cramer et al. (2016) and Louise et al. (2018) [10, 11]. Varying inclusion criteria might explain the differences, e.g. regarding language and inclusion of acceptance- vs. mindfulness-based approaches administered in group vs. individual settings, and differences in treatment protocols (session components, duration, and instructor experience [16]).

Next to positive and negative symptoms, depressive symptoms show high prevalence rates in SSD, with 29% of individuals with SSD fulfilling the criteria for clinically significant comorbid depression [17]. Depressive symptoms in SSD are associated with poorer clinical outcomes and disease progression as well as with heightened suicide risk [18–20], which makes early detection and treatment highly important. A study by Bergmann et al. (2021) [21] found higher mindfulness in SSD to be associated with lower depressive symptoms and meta-analyses by Jansen et al. (2019) [13] as well as Louise et al. (2018) [10] reported that mindfulness- and acceptance-based interventions are especially effective in treating depressive symptoms in SSD (g = 0.14–0.80). The evidence base regarding depressive symptoms, however, remains inconclusive, as Cramer et al. (2016) [11] and Yip et al. (2022) [15] did not find significant effects on affective symptoms in their meta-analyses. This discrepancy could be explained by the meta-analyses’ inclusion of trials in different languages and with varying treatment programme structures. Taken together, even though there is a growing body of evidence depicting the beneficial effects of mindfulness for symptom reductionin SSD, these results underline the importance of continuative research and further advances in this area.

Apart from the question of which specific symptoms change through mindfulness, the mechanisms behind these effects are poorly understood. Patients with SSD might benefit from MBIs as they develop an altered relationship with their symptoms and create a more accepting attitude towards and a capacity to disengage from distressing experiences such as hallucinations or delusions [22]. This could reduce symptom-related stress, as patients with SSD frequently become engrossed by their symptoms or engage in dysfunctional behaviours such as avoidance strategies [11]. Shapiro et al. (2006) [23] claim that improving cognitive, emotional, and behavioural flexibility might be one mechanism through which mindfulness exerts its positive effects. In recent years, psychological flexibility (PF) was often associated with clinical change within the mindfulness framework [24]. PF can be defined as the ability to consciously interact with the present moment in an accepting way, driven by chosen values and long-term goals rather than distressing internal experiences [25]. Compared to healthy individuals, patients with SSD were less psychologically flexible [26, 27]. The increase of PF is also the primary target in acceptance and commitment therapy (ACT), one of the most widely used manualized approaches in acceptance and mindfulness-orientated approaches [28, 29].

According to the theory framework of ACT, one process that is central to PF, as well as a cornerstone of psychopathology, is cognitive fusion (CF) [28]. CF represents the phenomenon in which behaviour is overly regulated and influenced by cognition rather than external information and where people interpret their thoughts literally rather than recognizing them as transient states [30–32]. Distancing from these inflexible thoughts is known as cognitive defusion [31]. In conclusion, if persons show high CF, i.e., they identify with various internal states and thoughts, and their cognition is less psychologically flexible, which results, according to ACT, in the need to apply interventions aiming at cognitive defusion.

Individuals with SSD showed significantly more frequent signs of CF than healthy controls [32]. CF was also found to be related to lower levels of mindfulness [33, 34] as well as to poor mental health outcomes such as depression and anxiety [31, 35, 36]. Furthermore, several studies indicate that CF mediates the relationship between mindfulness and negative affect [37, 38] as well as symptoms of depression and anxiety in healthy individuals [36] and negative symptoms [24, 26] as well as depressive symptoms in SSD [26].

Henceforth, the present study aimed to investigate the mediating role of PF in the relationship between mindfulness and positive, negative, and depressive symptoms in SSD within a cross-sectional study design.

It was hypothesized that in individuals with SSD (H1) mindfulness is negatively correlated with (H1a) positive symptoms, (H1b) negative symptoms, and (H1c) depressive symptoms. Furthermore, it was expected that (H2) mindfulness is positively correlated with PF; and lastly, that (H3) PF mediates the relationship between mindfulness and (H3a) positive symptoms, (H3b) negative symptoms as well as (H3c) depressive symptoms.

2.1 Design

A cross-sectional study design was used to assess atemporal mediation models according to Winer et al. (2016) [39], with PF as a mediator between mindfulness and positive symptom severity (Model A), negative symptom severity (Model B), and depressive symptom severity (Model C). The differentiation between negative and depressive symptoms, along with their separate assessment - an aspect often overlooked in studies involving patients with SSD - is of significant importance. This is due to the syndromal overlap between these concepts, even though they depict separable symptom domains [40]. An overview of the overall model can be seen in Figure 1. Data originates from three trials (see Figure 2) and was collected between June 2018 and May 2023. It was recorded tablet-based via REDCap [41], a web-based software platform designed for data collection and management in research studies, and securely and pseudonymously stored and processed.

2.2. Participants and Procedure

Participants were recruited from the inpatient ward for psychotic disorders, the psychiatric day clinic as well as the outpatient facility of the Charité – Universitätsmedizin Berlin, Campus Benjamin Franklin, Germany. Patients aged 18 or older with an ICD-10 F2x.x spectrum diagnosis assessed by a licensed psychiatrist willing to participate and provided informed consent were eligible to participate in the study and were approached by a research assistant. Ten patients participated in more than one of the three studies. In these cases, only the most recent data was used for analysis. Patients with severe positive symptoms, as indicated by a score of seven on any item on the Positive Syndrome Subscale of the Positive and Negative Syndrome Scale (PANSS), a neurological disorder or an acute substance dependence, apart from nicotine, were excluded from participation. The participation in the study was entirely voluntary, and withdrawal was possible at any time.

2.3. Measures

Besides assessing the demographic data, all participants completed three self-rating questionnaires and one clinician-rated measure in German language.

2.3.1. Mindfulness

To measure mindfulness, the German version of the Southampton Mindfulness Questionnaire (SMQ) was administered [42]. It refers to the past seven days and conceptualizes mindfulness as four related aspects: (1) decentered awareness, (2) letting go, (3) non-judgment, and (4) non-aversion. The SMQ comprises 16 items that are rated on a seven-point Likert scale ranging from (6) “agree totally” to (0) “disagree totally”. Consequently, the total score ranges from 0 to 96, with a higher score indicating higher mindfulness. The internal consistency was good, with a Cronbach’s α = .89 [42]. In this sample, a Cronbach’s α of .70 was found.

2.3.2. Symptom Severity

For the assessment of the severity of positive and negative symptoms, the Positive and Negative Syndrome Scale (PANSS) was employed [43]. The PANSS assesses three symptom domains: positive symptoms, negative symptoms, and general psychopathology. It consists of 30 items that are rated on a seven-point Likert scale, with higher scores indicating greater symptom severity, ranging from (1) “absent” to (7) “extreme”. The positive scale and the negative scale consist of seven items each. The internal consistency was satisfactory, with Cronbach’s α = .62 for PANSS positive scale, α = .92 for PANSS negative scale, and α = .55 for PANSS general scale [44]. In this sample, the internal consistency for the PANSS positive scale was α = .68, and for the PANSS negative scale α = .74.

The depression subscale of the German version of the Depression Anxiety Stress Scale (DASS-21) was used to measure the severity of depressive symptoms in clinical and nonclinical samples [45]. This questionnaire consists of 21 items, with seven items representing the depression domain. Participants are asked to rate how much each statement applied to them over the past week on a 4-point Likert scale ranging from (0) “did not apply to me at all” to (3) “applied to me very much or most of the time”. The total score for each domain can range from 0 to 21, with higher scores indicating greater severity of symptoms. In clinical and nonclinical samples, depressive symptoms are considered either normal (0 – 9), mild (10 – 13), moderate (14 – 20), or severe (21). The German version of the DASS-21 has demonstrated excellent internal consistency (Cronbach’s α = .91) for the depression subscale [46]. For the current study, the reliability of the depression subscale was excellent as well (α = .85).

2.3.3. Psychological Flexibility

To measure PF, the German version of the Cognitive Fusion Questionnaire (CFQ) was employed [47]. The questionnaire is a self-report measure with seven items that are scored on a 7-point Likert scale, ranging from (7) “always true” to (1) “never true”. The total score can range from 7 to 49, with higher scores indicating higher CF, which indicates lower PF. Previous research demonstrated that the CFQ has excellent internal consistency, with Cronbach’s α = .95 [47]. The present study showed an α of .85.

2.4. Statistical Analysis

Data were analysed with the R program for Statistical Computing (version 4.2.3) for macOS [48]. First, Pearson’s correlation coefficients were calculated to check if the (H1) SMQ sum score is significantly related to the (H1a) PANSS positive scale sum score, (H1b) PANSS negative scale sum score, and (H1c) DASS-21 depression scale sum score, as well as to the (H2) CFQ sum score. For hypotheses 3a-c, analyses of mediation models based on the ordinary least squares regression method were carried out using PROCESS Model 4 [49], with the sum score of each, the PANSS positive scale (Model A), the PANSS negative scale (Model B) and the DASS-21 depression scale (Model C) being the DV, mindfulness being the IV, and CFQ sum score as mediator. To evaluate linearity, plots were visually inspected. Potential outliers were identified using Cook’s distance, and excluded if scores were above .03. Bootstrapping, a robust procedure independent of distributional properties of the dataset [50], with 10,000 estimates, was applied to compute inferential statistics and 95% confidence intervals for the effects, which were assumed significant if zero was not included. In all analyses, a significance level of α = .05 was applied. Power was analysed post hoc using an application by Schoemann et al. (2017) [51] for simple and complex mediation models based on Monte Carlo simulations and bootstrapped confidence intervals for the indirect effect. This method calculates power estimates by dividing the number of replications in which the indirect effect of interest is significantly different from zero by the total number of replications.

3.1. Description of the Sample

The total sample consisted of N = 94 participants, after 29 outliers were excluded as they exceeded a pre-determined Cook’s distance score of .03. The age of the participants ranged between 19 and 74 years (M = 43.23, SD = 14.02). Five participants were older than the initial exclusion criterion of a maximum age of 65 years, as this criterion was removed in the YING study retroactively. Sixty participants (64%) identified with the male gender, 33 as female, and one as non-binary. When participating in the study, the participants had an SSD diagnosis for an average of 13.96 years (SD = 11.07; range: 0–43). Eighty-two participants indicated German citizenship, four Turkish citizenship, three Vietnamese citizenship, and five other nationalities. Further sample descriptions are displayed in Table 1. The mean DASS-21 score for the depression subscale is within the normal range (0–9) of clinical and nonclinical samples, according to the manual of the DASS-21 [52]. Compared to the average PANSS scores obtained in the original publication of the scale by Kay et al. (1987) [43] with a sample of inpatients, scores in this sample were, on average, one point above on the negative symptom scale (M_{current sample} = 22.24 vs. M_{Kay et al., 1987} = 21.01) and similar on the positive symptom scale (M_{current sample} = 17.81 vs. M_{Kay et al., 1987} = 18.20).

Table 1

*Sociodemographic characteristics of the sample (N = 94)*
Variables		n (%) \| mean (SD)/range
Age (years)		43.23 (14.02)/19–65
Diagnosis
	F20	73 (77.66%)
	F21	1 (1.06%)
	F22	1 (1.06%)
	F23	3 (3.19%)
	F25	15 (15.96%)
	F29	1 (1.06%)
Recruitment site
	Outpatient, Inpatient	36 (38.30%), 58 (61.70%)
Duration of disease (years)		13.96 (11.07)/0–43
Gender
	Female, Male, Diverse	33 (35.12%), 60 (63.83%), 1 (1.06%)
Nationality
	German	82 (87.23%)
	Turkish	4 (4.26%)
	Vietnamese	3 (3.19%)
	Other	5 (5.32%)
Marital status
	Unmarried	68 (72.34%)
	Married	8 (8.51%)
	Divorced	17 (18.09%)
	Widowed	1 (1.06%)
Housing situation
	Private flat	78 (82.98%)
	Shared flat	6 (6.38%)
	Assisted living	10 (10.64%)
Children	Yes, No	25 (26.60%), 69 (73.40%)
Educational level
	No school-leaving certificate	3 (3.19%)
	Primary school	12 (12.77%)
	Secondary school	24 (25.53%)
	A-levels	19 (20.21%)
	Technical college	4 (4.26%)
	Apprenticeship	12 (12.77%)
	Studied	20 (21.28%)
Work situation
	Unemployed	29 (31.18%)
	Retired	34 (36.56%)
	Student/apprentice	8 (8.60%)
	Self-employed	3 (3.23%)
	Employed	14 (15.05%)
	Other	5 (5.38%)
Note. SD = Standard deviation.

3.2. Zero-order Correlations

As predicted in Hypothesis 1, there was a small-to-moderate negative zero-order correlation between mindfulness assessed by the SMQ and the PANSS positive scale (r = − .24, p < .05), as well as the depression subscale of the DASS-21 (r = − .26, p < .05). Regarding the SMQ subscales, only “Absence of Aversion” showed a significant moderate-to-strong negative correlation with the PANSS positive scale (r = − .43, p < .01), while all subscales but “Non-Judgment” correlated significantly with the depression subscale of the DASS-21 (see Table 2).

The correlation between mindfulness and the PANSS negative scale (r = − .09, p = .39) showed a negative direction, but was not significant. As mediation analyses do not impose evidence of simple associations between IV and DV as a precondition [49, 53], Hypothesis 3b was not rejected, and mediation analysis of the effect of SMQ total scores on PANSS negative scores with CFQ scores as the mediating variable was still examined.

As predicted in Hypothesis 2, the SMQ correlated positively with PF, shown by the significant moderate-to-strong negative correlation with the CFQ scores (r = − .41, p < .01), as CF is a process negatively impacting PF. For a more detailed overview, see Table 2.

Table 2

*Pearson Correlations r (N = 94)*
Variables	1	2	3	4	5	6	7	8	9
1 SMQ total	-
2 SMQ Mindful Observation	.78**	-
3 SMQ Letting Go	.79**	.50**	-
4 SMQ Absence of Aversion	.61**	.30**	.28**	-
5 SMQ Non-Judgment	.67**	.40**	.44**	.12	-
6 PANSS - Positive Scale	− .24*	− .20	− .12	− .43**	.11	-
7 PANSS - Negative Scale	− .09	− .07	− .04	− .06	− .09	.40**	-
8 DASS-21 - Depression Scale	− .26*	− .22*	− .21*	− .16*	− .13	.16	.24*	-
9 CFQ	− .41**	− .28**	− .43**	− .23*	− .24*	.25*	.29**	.61**	-

Note. SMQ = Southampton Mindfulness Questionnaire; PANSS = Positive and Negative Syndrome Scale; DASS-21 = Depression, Anxiety and Stress Scale; CFQ = Cognitive Fusion Questionnaire.

*p < .05, **p < .01.

3.3. Process Analysis

The recruitment site of either the in- or outpatient unit at Charité was included as a covariate in all PROCESS models, based on the studies by Bergmann et al (2021) [21] and Böge et al. (2022) [24]. Correlations of the primary outcome variables with recruitment sites can be seen in Table 3. Participants in the inpatient ward displayed significantly higher scores on the CFQ and PANSS positive scale. The exact results, including t- and p-values can be seen in Table 4.

Table 3

*Correlations with the Covariable Recruitment Site (N = 94)*
	SMQ total	PANSS PS	PANSS NS	DASS-21 DS	CFQ
Recruitment Site	.13	− .27**	− .20	− .19	− .21*

Note. SMQ = Southampton Mindfulness Questionnaire; PANSS = Positive and Negative Syndrome Scale; PS = Positive Scale; NS = Negative Scale; DASS-21 DS = Depression Scale of the Depression, Anxiety and Stress Scale – 21 Items; CFQ = Cognitive Fusion Questionnaire.

*p < .05, **p < .01.

Table 4

*Mean Differences in Recruitment Site (N = 94)*
	Inpatient Ward (n = 58) M (SD)	Outpatient Facility (n = 36) M (SD)	t-test
SMQ total	45.55 (8.95)	48.39 (13.21)	t = -1.24, p = .22
CFQ	27.74 (7.56)	24.33 (8.30)	t = 2.78, p < .05
DASS-21 Depression Scale	7.71 (4.76)	5.89 (4.37)	t = 1.86, p = .07
PANSS Positive Scale	18.91 (4.81)	16.03 (5.64)	t = 2.64, p < .01
PANSS Negative Scale	23.12 (5.76)	20.83 (4.99)	t = 1.97, p = .05

Note. Patients from the day clinic (n = 3) were counted as inpatients. SMQ = Southampton Mindfulness Questionnaire; CFQ = Cognitive Fusion Questionnaire; DASS-21 = Depression, Anxiety and Stress Scale – 21 Items; PANSS = Positive and Negative Syndrome Scale.

3.3.1. Model A (Positive Symptom Severity)

After controlling for the recruitment site as a covariate, a total effect of mindfulness on positive symptom severity was found, B = − .10, p < .05. Mindfulness explained R² = .11 of the variance of positive symptoms (F(2,91) = 5.72, p < .01). When PF was added to the model as a mediator, it was significantly predicted by mindfulness, B = − .29, p < .01. However, PF did in turn not predict positive symptom severity, B = .10, p = .18. The model including PF was significant, F(3,90) = 4.45, p < .01, and explained R² = .13 of the variance of positive symptoms. The indirect effect of the complete mediation model (ab = − .03) did not reach significance, as the 95% bias-corrected confidence interval based on 10,000 bootstrap samples did include zero 95% CI [-0.07, 0.01]. Results are visualized in Fig. 3. A post hoc Monte Carlo power analysis revealed a power of .38, indicating that the indirect effect significantly differed from zero in 38% of the bootstrap replications.

3.3.2. Model B (Negative Symptom Severity)

There was no significant total effect of mindfulness on the severity of negative symptoms, B = − .03, p = .54. Mindfulness explained R2 = 0.04 of the variance of negative symptoms (F(2,91) = 2.12, p = .13). According to Rucker et al. (2011) [54] and Zhao et al. (2010) [55], a total effect of the IV on the DV is not a prerequisite for mediation, as the indirect effect describes the pure effect of mediation. After entering PF as the mediator into the model, mindfulness predicted PF significantly, B = − .29, p < .01, which in turn predicted the severity of negative symptoms significantly, B = .19, p < .05. The model including PF was significant, F(3,90) = 3.57, p < .05, and explained R2 = .11 of the variance of negative symptoms. Based on the significance of paths a and b, mediation is already shown, according to MacKinnon (2012) [56]. Additionally, the 95% bias-corrected confidence interval of the indirect effect (ab = − .06) did not include zero 95% CI [-0.11, -0.01], indicating that PF fully mediates the relationship between mindfulness and negative symptom severity. Results are visualized in Fig. 4. A post hoc Monte Carlo power analysis revealed a power of .78 for the indirect effect, indicating that the indirect effect was significantly different from zero in 78% of the bootstrap replications.

3.3.3. Model C (Depressive Symptom Severity)

An effect of mindfulness on depressive symptoms in the absence of PF was observed, B = − .10, p < .05. Mindfulness explained R² = .09 of the variance of depressive symptoms (F(2,91) = 4.56, p < .05). After entering PF as the mediator into the model, mindfulness predicted the mediator significantly, B = − .29, p < .01, which in turn predicted depressive symptoms significantly, B = .35, p < .01. The model including PF was significant, F(3,90) = 17.97, p < .01, and explained R² = .37 of the variance of depressive symptoms. The direct effect of mindfulness on depressive symptoms was no longer significant when the mediator was included, which shows that PF fully mediates the relationship between mindfulness and depressive symptoms, indirect effect ab = -0.10, 95% CI [-0.17, -0.04]. Results are visualized in Fig. 5. A post hoc Monte Carlo power analysis revealed a high power of .99 for the indirect effect, indicating that the indirect effect was significantly different from zero in 99% of the bootstrap replications.

The present study aimed at investigating the interplay of mindfulness, positive, negative, and depressive symptoms in persons with SSD as well as PF as a potential mediator in this relationship. First, it was hypothesized that mindfulness is negatively correlated with symptom severity regarding positive (H1a), negative (H1b), as well as depressive symptoms (H1c), and secondly, positively correlated with PF (H2). Furthermore, it was expected that PF mediates the relationship between mindfulness and positive (H3a), negative (H3b), and depressive symptoms (H3c).

Regarding the first hypothesis, positive as well as depressive symptoms were significantly negatively correlated with mindfulness. The results regarding positive symptoms are in line with Böge et al. (2022) [24], showing positive yet not negative symptoms to be significantly correlated with mindfulness. As mindfulness practice can lead to positive emotional experiences such as feelings of calmness and peacefulness [57], the worsening of positive symptoms through emotional distress (especially anxiety) might be reduced [58]. Enhanced metacognitive skills, such as improved interoceptive awareness, might reduce the belief in negative consequences of psychotic symptoms [59], by which the exacerbation of positive symptoms could also be mitigated. The fact that the mindfulness subscore “Absence of Aversion” showed by far the largest correlation with positive symptoms (r = -.43, p < .01) might underline the importance of the ability to accept experiences such as acoustic hallucinations or delusional beliefs, not reacting with anger, the need to push these away, or distract oneself, in probably reducing symptom-related distress and hence the triggering of these symptoms. Accordingly, mindfulness interventions, e. g. meditation, focussing on accepting the present symptoms, might be more suitable for targeting positive symptoms.

Additionally, also the negative relationship between mindfulness and depressive symptoms was shown in previous research on patients with SSD [21,24]. Furthermore, this aligns with the findings of two recent meta-analyses, in which mindfulness- and acceptance-based interventions for persons with psychosis were shown to demonstrate the largest effects on depressive symptoms [10,13]. In this study, “Mindful Observation”, the ability to notice thoughts and feeling without reacting to them, and “Letting Go”, the ability to leave challenging cognitions as they are instead of ruminating or worrying, were mostly related to depressive symptoms in SSD. This corresponds with findings that rumination, characterised by repetitive thoughts about current concerns and negative experiences [60], possibly representing the counterpart to awareness [61], especially to “Mindfulness Observation” and “Letting Go”, is a primary factor contributing to depression [62,63]. As experts in both international (NICE) and national guidelines (S3) recommend MBIs as a treatment for depression now [64,65], the implementation of these in the treatment of SSD, of which up to 50% suffer from a comorbid depression [66], might be as well a promising step towards a more effective overall treatment of SSD.

In the present study, negative symptoms did not show a significant correlation with mindfulness, which is in line with the study by Böge et al. (2022) [24]. In comparison to negative symptoms, positive symptoms might be related to the concept of mindfulness more directly. In contrast, the role of mindfulness on negative symptoms, shown in some meta-analyses [e.g. 13,14], is delivered via certain mediators. Besides PF, also positive reappraisal [67], stigma resistance [68], an increase in positive emotions and anticipatory pleasure [69], improved metacognition [70] or a reduction in cognitive and emotional reactivity as well as repetitive negative thinking [71] might be mechanisms through which mindfulness excerpts its positive effect on negative symptoms, which should be explored in future studies.

The second hypothesis, that mindfulness is positively associated with PF, was supported by the moderate negative correlation of mindfulness and CF, inversely related processes of PF. This is in line with findings from studies including different populations [24,34,36], as well as with the theoretical background of ACT. In ACT, acceptance and mindfulness processes are used to cultivate PF, a broad, higher-level construct that captures six interconnected processes [72]. Furthermore, four of these processes of PF, namely contact with the present moment, accepting, cognitive defusion, and the conceptualized self, depict mindfulness and acceptance processes [28], which shows a solid theoretical interconnectedness of these two constructs. Instead of confusing thoughts and emotions with actual reality and letting these automatically guide behaviour, a more mindful behaviour might allow individuals to respond more flexibly and with less automaticity to different thoughts and emotions.

Regarding the third hypothesis, it could be shown that PF mediates the relationship between mindfulness and negative symptoms, as well as depressive symptoms, but not positive symptoms in SSD. This supports previous research, suggesting PF to be an essential mechanisms of change in acceptance- and mindfulness-based approaches [28,73]. Even if negative and depressive symptoms are distinct concepts, certain domains are common in both, such as anhedonia, avolition, and anergia [74,75] This underscores the significance of MBIs as transdiagnostic approaches, wherein conventional diagnostic demarcations are superseded, fostering novel avenues for comprehending mental well-being and its enhancement through potential symptom-cluster-specific interventions.

Through PF, emotion regulation might be enhanced, and positive feelings toward others could decrease symptoms of anhedonia, as supposed by Liu et al. (2021) [58], which would explain why PF mediates the effect of mindfulness on negative and depressive symptoms but not on positive symptoms. Regarding depressive symptoms, the finding is further underlined by the magnitude of its impact, as indicated by the large proportion of variance explained. Several other studies also show that PF has a superior contribution to differences in depressive symptoms than mindfulness in general [35,36,76]. The mediating function of PF between mindfulness and depressive symptoms is additionally supported by longitudinal data [77], indicating causal directions.

In negative and depressive symptoms occurring in the context of SSD, where also internalized stigma and shame are especially prevalent [78], the outcomes of this study indicate that a focus on cognitive defusion, as well as PF in general, might enhance the effectiveness of mindfulness-based therapies, which needs to be confirmed in future trials with randomized-controlled designs. This appears particularly relevant since the effects of existing pharmacological treatments as well as psychological interventions for SSD on negative symptoms did not show clinical significance according to a meta-analysis by Fusar-Poli et al. (2015) [79], but account for a large part of the poor functional outcomes and long-term disability in this population [80,81]. Results of the current study indicate that MBIs might be a treatment option suitable for targeting negative and depressive symptoms. Early treatment of these symptoms is essential as they are generally associated with poorer clinical outcomes as well as a heightened suicide risk in SSD [18,20]. Moreover, augmentation of a mindfulness-based group therapy with oxytocin was recently found to have an additive effect on the reduction of negative symptoms compared to a control group, receiving mindfulness-based group therapy and a placebo[82]. Oxytocin’s potential additive effects on depressive symptoms in MBIs for individuals with SSD sould be explored in future studies.

In positive symptoms, possibly different mechanisms of change might explain the effect of mindfulness on positive symptoms, as shown by some meta-analyses [11,12,15]. PF is a construct that includes six processes, of which five were not considered in this study (i.e., acceptance, being present, values, committed action, and the conceptualized self). It might be that positive symptoms are alleviated by being present or an accepting attitude rather than a detachment from the literal content of thoughts, an ability which the positive symptoms themselves might impede. Therefore, future studies are needed to investigate mechanisms of change concerning positive symptoms, helping to improve MBIs, refine treatment manuals, and facilitate a better selection of patients, depending on their symptoms, who may benefit from mindfulness-work. This study adds further evidence for a possible mechanism of action of the effect of mindfulness on negative and depressive symptoms in SSD using a large sample, including in- and outpatients, as well as the PANSS as a rater-based instrument in comparison to the Self-Evaluation of Negative Symptoms Scale (SNS) used by Böge et al. (2022) [24].

Nevertheless, these findings should be considered in light of some limitations. Given the study’s cross-sectional design, no causal conclusions can be drawn. The directions of the associations still need to be clarified, as no temporal precedence was assessed, and the positions of the variables in the mediation models could be interchangeable. For example, CF was found to predict next-day mindful awareness in a study by Berghoff et al (2018) [33], and mindfulness was found to be the mediator between PF and symptoms of depression in a study by Curtiss & Klemanski (2914) [83]. Furthermore, although recruitment site was included as a covariate in the statistical design, similar to the studies by Bergmann et al. (2021) [21] and Böge et al. (2022) [24], the medication regime, the understanding of the concept of mindfulness, and already existing experiences should be examined in future trials within a longitudinal design.

Moreover, the sample might not comprise the diversity in clinical pictures displayed in SSD, as most patients were diagnosed with an ICD-10 F20.x diagnosis (77%). Even though in- as well as outpatients were included, the sample displays mainly chronic stages of psychosis, with a mean duration of the disease of 13 years. This stage of illness is currently in the focus of research on the effects of mindfulness in SSD [84]. As mindfulness, PF, and symptom severity may interact differently in different stages of psychosis, different subtypes and stages of SSD should be investigated in future research.

Furthermore, mindfulness, PF, and depressive symptom severity were exclusively assessed with self-rated questionnaires. As there are potentially significant discrepancies between how mindful individuals believe themselves to be vs. how mindful they are in reality [85], which also accounts for depressive symptoms and PF, a mixed-methods approach combining the advantages of interviews, self-rating, as well as rater-based instruments should be implemented in future studies. Also, as Krynicki et al. (2018) [75] propose an overlapping, dimensional model of negative, positive, and depressive symptoms for SSD, future projects should examine not only additional mechanisms of mindfulness but also their effects on specific symptoms rather than symptom categories, to detect probable effects of mindfulness this study was not able to.

The present study provides novel insights into the relationship between mindfulness, PF, and symptom severity in SSD. Especially for the relationship of mindfulness with negative as well as depressive symptoms, our data indicate a crucial role for PF, which should be confirmed using longitudinal data. Our outcomes indicate that focusing on PF in MBIs might better target negative and depressive symptoms. Positive symptoms might be improved through either mindfulness work in general or a focus on other treatment mechanisms. These are to be investigated in future studies using more fine-grained analyses, as positive symptoms were associated with mindfulness, but PF was not found to mediate this effect. Taken together, the present study provides additional insights into refining treatment development and optimizing the therapeutic effectiveness of MBIs. Consequently, this might enhance their dissemination among individuals with SSD, a population that continues to face significant disadvantages regarding their access to modern and up-to-date treatment options.

Acknowledgements

None.

Ethics approval

The authors assert that all procedures contributing to this work comply with the ethical standards of the relevant national and institutional committees on human experimentation and with the Helsinki Declaration of 1975, as revised in 2008. All procedures involving human subjects/patients were approved by the ethical committee of the Charité – Universitätsmedizin Berlin (EA4/239/20, EA4/053/18, EA4/233/21).

Consent to participate

Written informed consent was obtained from all patients prior to their inclusion in the study.

Data availability

The data supporting this study’s findings are available from the corresponding author upon reasonable request.

Author contributions

Inge Hahne: Conceptualization, Data curation, Investigation, Methodology, Projectadministration, Resources, Supervision, Validation, Visualization, Writing – review & editing.

Julia Segerer: Formal analysis, Methodology, Writing – original draft, Writing – review & editing.

Marco Zierhut: Data curation, Writing – review & editing

Niklas Bergmann: Data curation, Writing – review & editing

Thi Minh Tam Ta: Resources, Writing – review & editing

Eric Hahn: Resources, Writing – review & editing

Kerem Böge: Conceptualization, Methodology, Project Administration, Supervision, Resources, Writing – review & editing

Competing interests

The authors declare that they have no competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. The studies were financed by internal funding from the Charité Universitätsmedizin Berlin.

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No competing interests reported.

The Relationship between Mindfulness, Psychological Flexibility, and Symptom Severity in Persons with Schizophrenia-Spectrum-Disorders – a Cross-Sectional Study

Status:

Version 1

Abstract

Figures

1. Introduction

2. Methods