Cognitive-behavioral treatment for insomnia and mindfulness-based stress reduction in nurses with insomnia: a non-inferiority internet delivered randomized controlled trial

The current study

Noninferiority randomized controlled trials (RCTs) are instrumental in appraising the effectiveness of emerging treatments in compared with established benchmarks (Piaggio et al., 2012). In this pivotal study, a noninferiority design plays a crucial role in meticulously evaluating emerging treatments, specifically focusing on standardized internet-delivered interventions such as the IMBSR, and comparing them against established benchmarks. A large body of evidence highlights the deleterious psychological impacts of the COVID-19 pandemic on frontline HCWs, and sleep-focused treatments are warranted to support their well-being (De Kock et al., 2021; Salari et al., 2020). Therefore, this study investigated the efficacy of internet-delivered CBT-I and MBSR for clinical nurses with insomnia.

The primary goal of this study was to assess whether internet-delivered MBSR for insomnia yields results that are at least as effective as those of ICBT-I in reducing insomnia among clinical nurses. The hypothesis was that the IMBSR would be noninferior to the ICBT-I by significantly reducing insomnia symptoms. The second aim of the study was to investigate the efficacy of internet-based formats for both MBSR and CBT-I in treating insomnia among nurses. It was hypothesized that both the IMBSR and ICBT-I would lead to significant improvements in insomnia severity, mindfulness, and depression following the intervention. Additionally, it was expected that the ICBT-I would lead to a greater decrease in the severity of insomnia and depression than the IMBSR.

Trial setting

The study was a two-armed, assessor-blinded, internet-delivered RCT with a parallel group noninferiority design and an equal allocation ratio (1:1) that compared the experimental intervention (IMBSR) with the standard treatment (ICBT-I). Ethical approval was granted from the Research Ethics Committee of Lorestan University of Medical Sciences (Approval No: IR.LUMS.REC.1399.269). The trial was prospectively registered at ISRCTN (ID: ISRCTN36198096) (Li, Nazari & Sadeghi, 2022). The trial spanned from June 2022 to May 2023.

The CONSORT (Consolidated Standards of Reporting Trials) checklist for noninferiority RCTs was followed to report this trial (Piaggio et al., 2012). Of the 240 clinical nurses screened for eligibility, 106 were excluded for various reasons, including 34 who declined to participate, 30 who had scheduling conflicts, 24 who did not meet a minimum cutoff score for clinical insomnia (15 points), and 18 who were found ineligible following clinical interviews. A total of 134 clinical nurses who met the eligibility criteria consented to participate in the study. The CONSORT diagram is presented in Fig. 1.

The inclusion criteria were as follows: (a) provided signed informed consent, (b) were actively employed as clinical nurses on the front lines of the COVID-19 pandemic, (c) were at least 18 years of age, and (d) internet access. The participants (e) received a formal diagnosis of insomnia based on the Structured Clinical Interview for DSM-5 Sleep Disorders (SCID-5-SD), (f) reported clinically significant moderate insomnia (15–21) to severe insomnia (22–28) symptoms on the Insomnia Severity Index (ISI) by scoring 15 points or more (Morin et al., 2009), and (g) demonstrated a willingness to participate. The exclusion criteria were as follows: (a) diagnosed with COVID-19, (b) received psychological treatment for insomnia within the last year, (c) missed three or more scheduled sessions, and (d) currently using complex or unstable sleep medication.

Procedure

Participants were recruited from June to December 2022 through online announcements, social media posts, public health forums, and word-of-mouth referrals. This multifaceted approach enabled the study to reach a diverse pool of potential participants, encompassing nurses from various workplaces with varying levels of experience and who represented diverse backgrounds. Additionally, nurses were encouraged to share information about the study with their colleagues, further broadening the participant base.

Eligible individuals could apply to participate in the study via email or phone. Participants received comprehensive information about the study’s objectives, potential benefits, associated risks, and expected duration. Additionally, participants were assured of the confidentiality and anonymity of their personal information, with the flexibility to withdraw their consent at any time during the study. Potential participants were invited to provide an email address to receive an invitation letter containing both the informed consent form and the primary outcome measure.

Only nurses who provided informed consent and had an insomnia severity index (ISI) score of 15 or higher progressed to the Structured Clinical Interview for Sleep Disorders (SCID). This in depth, one-hour online clinical interview was conducted by two clinical psychologists to rigorously assess participants against the eligibility criteria. This comprehensive screening process ensured that only individuals with clinically significant insomnia were included in the study, minimizing potential risks to participants and enhancing the validity of the study’s findings. Finally, eligible participants were randomized to receive either the IMBSR or ICBT-I intervention.

Interventions

Participants were requested to maintain their regular lifestyle throughout the study, including daily activities, exercise regimen, dietary habits, and medication routines. Additionally, any individuals undergoing psychological interventions needed to disclose such treatments. Both the IMBSR and ICBT-I commenced with an initial motivational interview module designed to motivate participants to change and improve their adherence.

The IMBSR program

The IMBSR program was administered in eight 2-hour weekly sessions (Kabat-Zinn, 2013; Teasdale, Segal & Williams , 2014), plus one 6-hour weekend intensive silent retreat. The course aimed to foster participants’ mindfulness and encourage them to respond adaptively to internal and external stressors. The core components of the program included (a) motivational interview, (b) theoretical underpinnings of mindfulness within the mind-body context to learn mindful awareness of the body, (c) practice of three formal mindfulness techniques: hatha yoga (followed by body scan), sitting meditation, and optional meditation, (d) cultivating mindful responses to stress and growing the ability to respond mindfully and deliberately to stress rather than falling into preconditioned, habitual, and reactive responses, and (e) plans for future practice and maintaining treatment gains, and (f) daily mindfulness practices and maintaining gains: participants received weekly homework assignments that reinforced the learned concepts. These may include practicing guided meditations at home (20–30 min), completing mindful movement exercises such as mindful yoga or body scans, and integrating mindful sleep hygiene practices into bedtime routines (e.g., mindful breathing exercises before bed) to promote a more sleep-conducive environment.

The ICBT-I program

The ICBT-I program included eight 2-hour weekly sessions (Edinger & Carney, 2015; Perlis & Al, 2008). The goal of CBT-I is to help individuals develop healthy sleep habits and overcome insomnia by addressing both behavioral and cognitive factors that contribute to sleep difficulties. The program consisted of (a) motivational interview, (b) sleep hygiene module, (c) stimulus control, (d) sleep restriction, (e) relaxation techniques (i.e., muscle relaxation, breathing exercise), (f) cognitive therapy (i.e., cognitive restructuring), and (g) preventing relapse (see Appendix 1 for a detailed description of interventions).

Outcomes

The outcome measures included the ISI, the nine-item Patient Health Questionnaire (PHQ-9; Kroenke, Spitzer & Williams, 2021), the 15-item Five Facet Mindfulness Questionnaire (FFMQ-15; Gu et al., 2016; Khanjani et al., 2022), and the Client Satisfaction Questionnaire-Internet (CSQ-I; Boßet al., 2016). The participants completed the self-reported instruments at Time 1 (baseline to allocation) and Time 2 (postintervention), with reminder emails sent within one week at each time point. The study timeline is presented in Table 1.

Primary outcome

Secondary outcome

Sample size

Sample size determination was meticulously conducted to adhere to stringent methodological standards, guided by the recommended minimal important difference (MID) for noninferiority trial designs, as elucidated by Hwang & Morikawa (1999). We set the noninferiority margin at half of the MID, equivalent to an eight-point reduction on the Insomnia Severity Index (ISI), based on the seminal work of Morin et al. (2011). With a significance level (α) of 0.05 and a power level of 80%, our power analysis was conducted meticulously to ensure robustness. Accounting for a projected 25% dropout rate, our calculated sample size of 134 participants was determined with precision to guarantee adequate statistical power.

Randomization

A permuted block randomization schedule was generated using a computerized random number generator and a random sequence of block sizes (i.e., 4, 6, and 8). The randomization schedule was stored in a secure location, and only authorized personnel had access to it. The independent investigator was responsible for assigning participants to the study arms. The randomization schedule was stored securely, and only authorized personnel had access to it. The treatment allocation was concealed from both the researchers and the participants until all posttreatment assessments had been completed.

Harms

Although CBT-I and MBSR are generally safe treatments for insomnia, the potential for adverse events and harm were systematically monitored throughout the trial. Participants who exhibited heightened psychological distress, temporary sleep disruption, worsening insomnia, depersonalization, or other concerns were offered support by licensed clinical psychologists and general practitioners through both email and telephone consultations. The clinical team underwent comprehensive training in psychological assessments, structured interviews, and ethical considerations in clinical research.

Statistical analyses

All statistical analyses were conducted using the SPSS software (version 25; IBM Corp., Armonk, NY, USA). Two-tailed tests were employed, with a significance level (alpha) set at 0.05, except for the noninferiority analysis, which utilized a one-tailed test. Adopting an intent-to-treat (ITT) approach, all initially randomized participants were included, irrespective of withdrawal or dropout. Missing data were handled through imputation using the last observation carried forward (LOCF) method, substituting missing data points with the most recent recorded values. Descriptive statistics were utilized to calculate demographic characteristics and outcome measures. Categorical variables were analyzed using chi-square tests, while continuous variables were examined using with independent t tests. Program feasibility and acceptability were assessed through the recruitment rate, retention rate, and client satisfaction using the CSQ-I.

In the context of a noninferiority trial, the F-statistic test and the corresponding p-value were applied to assess the variance between the two treatment groups. This step is pivotal because differing variances can influence the power of the noninferiority test. A 95% confidence interval (CI) approach was employed to test the noninferiority of the IMBSR in compared with the ICBT-I, with a noninferiority margin set at 4 points on the ISI score (Mascha & Sessler, 2011). The p value estimates the likelihood that the mean ISI score for IMBSR is significantly smaller than the mean for ICBT-I plus the noninferiority margin of 4.0, assuming that the null hypothesis is valid. In this instance, the null hypothesis posits that the experimental intervention (IMBSR) is inferior to the standard treatment (ICBT-I) by a margin equal to or greater than 4 points on the ISI. Noninferiority was confirmed if the upper bound of the one-tailed 95% CI of the mean difference between the groups on ISI score was less than 4 points in favor of the ICBT-I.

To compare the efficacy of ICBT-I with that of IMBSR, univariate analysis of covariance (ANCOVA) was performed on the ISI, PHQ-9, and FFMQ-15, with Time1 data serving as a covariate to mitigate bias (i.e., preexisting group disparities). The assumptions, including a normal distribution, equal error variances, and homoscedasticity, were verified before conducting the ANCOVA. Treatment effects are presented in terms of Cohen’s d and partial eta-squared (η²p) values. Paired t tests were computed to evaluate within-group changes between Time 1 and Time 2. The number of participants exhibiting subthreshold insomnia at Time 2 was also reported.

Descriptive characteristics

The descriptive characteristics of the sample are presented in Table 2. At baseline, t tests revealed no significant differences in continuous variables, indicating successful randomization. The study included 134 clinical nurses aged 25 to 48 years (M = 33.12 years; SD = 5.53). This sample population had a significant association with marital status (χ² = 9.67, p = 0.002), with a larger proportion being in relationships (64.9%, n = 87) than single (35.1%, n = 47). The retention rate was 55%, with 77.6% (n = 104) of participants completing the study. At Time 2, 82% (n =55) of the ICBT-I participants and 73% (n =49) of the IMBSR participants completed the programs. The CSQ-I showed high satisfaction with the ICBT-I (M = 26.37, SD = 4.87) and the IMBSR (M = 27.69, SD =3.99).

Treatment results

According to the pretreatment data, there was no significant difference in variance between the two treatment groups (F-statistic = 0.28, P = .59). At Time 2, the estimated marginal mean ISI score for the IMBSR (M = 14.99) exceeded that of the ICBT-I (M = 10.93) by 4.06 points. The upper limit of the one-tailed 95% CI for the mean difference is 4.88, which was greater than the non-inferiority margin of 4. The p-value of 0.46 indicates that there is not sufficient evidence to reject the null hypothesis of inferiority, indicating that the IMBSR did not prove to be noninferior to the ICBT-I in reducing ISI scores at Time 2.

To ensure the robustness of the analysis, no violations of ANCOVA assumptions were identified (P > .05). The ICBT-I demonstrated significantly lower insomnia severity and depression scores than did the IMBSR. An ANCOVA was conducted to assess the effect of the intervention on insomnia severity, controlling for baseline scores. The analysis revealed a significant main effect of the intervention, F(1, 131) = 51.88, p < .001, η² p = .28. The effect size was large, indicating a substantial impact of the intervention on insomnia severity. The ANCOVA results highlighted a substantial decrease in the ISI score (F(1, 131) = 61.52, P < 0.001, η²p = 0.32, Cohen’s d =1.30, 95% CI [0.92–1.68]) and a lower PHQ-9 score (F (1, 131) =28.65, P < 0.001, η²p = 0.14, Cohen’s d = 0.71, 95% CI [0.34–1.08]) for the ICBT-I. Conversely, the IMBSR participants reported higher mindfulness scores at Time 2 (F (1, 131) = 20.14, P < 0.001, η²p = 0.13, Cohen’s d =  − 0.67, 95% CI [−1.01 to −0.32]).

Within-group differences showed that both the IMBSR and ICBT-I were effective at reducing insomnia severity and depression severity and improving mindfulness. At Time 2, the paired t test results showed that IMBSR led to significant reductions in insomnia severity (t (66) = 7.64, p < .001) and depression severity (t (66) = 5.15, p < .001) and improvements in mindfulness (t (66) = 8.32, p < .001). At Time 2, the paired t test results showed that ICBT-I led to significant reductions in insomnia severity (t (66) = 13.58, p < .001) and depression severity (t (66) = 11.56, p < .001) and improvements in mindfulness (t(66) = 2.32, p = .02). Additionally, a total of 83 participants (62.0% of the sample, n = 134) reported ISI scores lower than 15, indicating no moderate clinical insomnia. Within the treatment groups, there were 30 participants (44.8%) in the IMBSR group and 53 participants (79.1%) in the ICBT-I group. These findings suggest that a significantly greater proportion of participants in the ICBT-I group achieved scores indicative of no moderate clinical insomnia than did those in the IMBSR group. The means and standard deviations for the treatment outcomes are presented in Table 3.

Limitations

The novel aspects of this study contribute to its clinical and theoretical significance. However, the study also has some limitations. One primary limitation of this trial was the absence of a placebo group. A placebo group would have allowed for a more robust evaluation of the specific effects of ICBT-I and IMBSR. The lack of objective and biological measures (e.g., actigraphy or polysomnography) was another limitation of this trial. Without follow-up data, we were unable to evaluate the long-term effects of the programs. Further studies with follow-up data are needed to determine the long-term durability of ICBT-I and IMBSR. The nurses were generally familiar with sleep hygiene and RCTs. Therefore, as well-educated participants, they may have been able to obtain more benefits from the delivered programs. Both programs were conducted via the internet. Therefore, the nurses were not limited by physical, geographical, or occupational problems, which increased the generalizability of the study. However, nurses without internet access were excluded from participation. Additionally, the online format may have made it more difficult for the therapists to monitor participants’ progress. The researchers took into account a potential 25% dropout rate when determining the sample size, resulting in a sample of 134 participants. This careful consideration of attrition rates enhances the study’s generalizability and its capacity to withstand participant attrition.