Participants will receive a 12-hour iMBCT-I treatment. MBCT-I consists of weekly 1.5-h sessions over 8 weeks online through the Tencent Meeting, with mindfulness practice as homework six times a week.

The iMBCT-I program was adapted from the original format of Segal et al., which targeted mainly depression and consisted of eight 2.5-hour sessions held on a weekly basis (20). The modification mainly followed the MBCT-I in Wong SY and colleagues’ research, making it tailored for CID patients (22). Due to the limitation that Tencent Meeting displays a maximum of 25 members’ videos per page, we set the maximum group capacity to 20 individuals to ensure that all members can consistently maintain face-to-face interaction online.

The iMBCT-I program will be conducted by certified instructors with over 2 years of experience in teaching MBCT. Prior to the treatment, an initial orientation session will be held to clarify the objectives and tasks for the 8-week duration and to facilitate mutual acquaintance among group members. Thereafter, the weekly sessions will be conducted according to the respective theme. Themes of iMBCT-I are Awareness and Automatic Pilot (week 1), Recognizing the Dysfunctional Beliefs in Insomnia (week 2), Thoughts Are Not Facts (week 3), A New Perspective (week 4), Awareness is the Start of Change (week 5), Allowing/Letting Be (week 6), “How Can I Best Take Care of Myself?” (week 7) and Maintaining and Extending New Learning (week 8). The program includes sequential instruction in mindfulness practices such as body scan, mindful eating (raisin exercise), pleasant/unpleasant events calendar, sitting meditation, “seeing” or “hearing” exercise, 3-minute breathing space, mindful stretching, and walking. In addition, the iMBCT-I program includes both cognitive and behavioral elements. The cognitive component of iMBCT-I primarily includes psycho-education related to sleep hygiene, covering the nature of sleep and insomnia, which are factors influencing sleep and good/bad sleep habits. Simultaneously, participants are taught to identify ruminative or dysfunctional thoughts associated with insomnia, foster awareness of these thoughts, explore the accompanying feelings and emotions that emerge in response to insomnia, and approach all of them with an accepting and nonjudgmental mindset. Unlike CBT-I, the philosophy of iMBCT-I is to cultivate an accepting, nonjudgmental relationship with those beliefs, thoughts and emotions instead of challenging them. The behavioral components include sleep hygiene, sleep restriction and stimulus control, following the guidelines outlined in the CBT-I manual. Approximately 80% of the course time is dedicated to the mindfulness component, whereas the remaining 20% focuses on the CBT-I component.

Participants will receive a 1.5-hour initial sleep hygiene education session online through the Tencent Meeting. The online sleep hygiene education session will be carried out according to the Sleep Health Management Handbook recommended by the Chinese National Health Commission (41). It delivers standardized content covering insomnia symptoms and their impact, prevalence and underlying causes. In addition, it provides guidance on when to seek medical assistance and offers basic lifestyle, environmental, and behavioral strategies to improve sleep quality.

The choice of a one-time SHE session as the control condition aligns with prior studies investigating other cognitive-behavioral interventions for insomnia (10, 42). While SHE differs in contact time from the iMBCT-I program, it serves as an active control condition that provides standardized, evidence-based sleep health knowledge without including structured mindfulness or cognitive-behavioral techniques. This approach allows us to isolate the specific effects of iMBCT-I from general educational benefits while maintaining ecological validity.

Participants in the SHE group will be attention-matched with those in the iMBCT-I group to control for expectancy and engagement effects. First, both groups will receive standardized informed consent, which clearly states: “This study compares two different approaches to improving sleep. You will be randomly assigned to one of the following: Program A – improving sleep through iMBCT-I, or Program B – improving sleep through SHE. Both are evidence-based, but it is currently unclear which is more suitable for most people.” This framing is intended to equalize treatment expectancy across groups. Second, both interventions will be delivered in an online group format via Tencent Meeting. Third, to maintain comparable levels of engagement and attention, participants in the SHE group will be asked to keep sleep diaries, just as in the iMBCT-I group. Research assistants will send daily reminders via smartphone to facilitate compliance. Considering that the iMBCT-I group will receive seven additional weeks of structured intervention, the SHE group will be administered seven weekly follow-up questionnaires to maintain engagement parity. These questionnaires will include items such as “How has your sleep been over the past week?” and “Which aspects of the sleep hygiene education have you applied?” Fourth, both groups will receive the same incentive: a free actigraphy upon completion of the study. Finally, post-intervention satisfaction assessments will be conducted for both groups to evaluate their subjective experiences with the respective interventions.

In this study, the Insomnia Severity Index (ISI) will be used to measure the severity, nature and impact of insomnia (43). It consists of 7 items and is rated on a 5-point scale ranging from 0 (no problem) to 4 (very severe problem). A total score of 8–14 suggests subclinical insomnia, and a total score over 14 indicates clinical insomnia. A reduction in ISI scores of 8 or more points from baseline is regarded as a response to treatment, and an absolute score on the ISI of 7 points or less is regarded as remission (44, 45). The Chinese version of ISI was translated and validated by Yang et al. and its Cronbach’s α was 0.94 (46). And it is supported to be a valid outcome measure for CBT-I by literature (47).

At baseline, demographics (e.g. age, gender, marital status, educational background, income), related clinical data (e.g. use of medication) and descriptive data on lifestyle practices (e.g. smoking and alcohol use).

Sleep quality is assessed by the Pittsburgh Sleep Quality Index (PSQI). The PSQI is a self-rated questionnaire comprising 19 individual items that generate seven component scores: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication and daytime dysfunction (48). These components are then summed to a total score, which ranges from 0 to 21, with higher scores indicating poorer sleep quality. The Chinese version demonstrated high internal consistency, and its Cronbach’s α was 0.83 (49).

The Five Facet Mindfulness Questionnaire (FFMQ) is a 39-item instrument that measures five distinct facets of mindfulness, namely observing, describing, acting with awareness, non-judging, and non-reacting (50). It is scored using a 5-point Likert scale, ranging from 1 (never or very rarely true) to 5 (very often or always true). Those have greater mindfulness levels have higher total scores. The FFMQ has been translated into Chinese version and widely used in China. The Cronbach’s α of the Chinese version was 0.83 for the community sample and 0.80 for the clinical sample (51).

The Patient Health Questionnaire-9 (PHQ-9), a globally used tool to screen and measure the severity of depression, is applied to measure the depressive symptoms of CID patients in this study (52). It consists of 9 items, with a 4-point Likert scoring system, ranging from 0 (not at all) to 3 (nearly every day). The total score varies from 0 to 27. Scores of 5, 10, 15, and 20 represent mild, moderate, moderately severe, and severe depression, respectively (52). In Chinese population, the Cronbach’s α was 0.86 (53).

The Generalized Anxiety Disorder 7-item scale (GAD-7) is used to assess anxious levels by evaluating the frequency of being bothered by specific symptoms over the past two weeks (54). Each item is scored from 0 (not at all) to 3 (nearly every day). The total score ranges from 0 to 21. Scores of 5, 10, 15 represent mild, moderate and severe anxiety, respectively (54). GAD-7 has been validated among Chinese population, and the Cronbach’s α was 0.90 (55).

To assess health related quality of life, the SF-12 Health Survey is used, which contains 12 items and 2 subscales: physical component summary (PCS) and mental component summary (MCS) (56). Through standardized transformation models, these scores are converted into normalized scores ranging from 0 to 100, with higher scores suggesting better health related quality of life. The psychometric properties have been confirmed for Chinese population, with Cronbach’s α being 0.86 (57).

The Attitudes Toward Seeking Professional Psychological Help Scale-Short Form (ATSPPH-SF) is a revised 10-items instrument designed to assess attitudes toward psychotherapy (58). The scale comprises three dimensions: openness to seeking professional help, perceived effectiveness of professional help and preference for independent problem-solving. Each item is rated on a 4-point Likert scale (0 = strong disagreement and 3 = strong agreement), with some items reverse-scored. Higher total scores demonstrate more positive attitude toward psychotherapy. The ATSPPH-SF has been translated and validated among Chinese population, with Cronbach’s α values ranging from 0.71 to 0.82 for its subscales and total score (59). In order to collect the attitude towards online psychotherapy, an adapted version of ATSPPH-SF is applied, with the term “psychotherapy” being replaced by “online training” thoroughly (60).

To assess sleep-related cognition, the Dysfunctional Beliefs and Attitudes about Sleep Scale 16-item version (DBAS-16) is used (61). Items are scored on a 5-point Likert scale (1=strongly agree and 5= strongly disagree), with lower scores indicating severer dysfunctional beliefs and attitudes. The DBAS-16 comprises four subscales, namely consequences of insomnia, sleep worry, sleep expectations, and medication. The DBAS-16 has been validated among Chinese population, with a Cronbach’s α value of 0.80 (62).

Sleep parameters include sleep onset latency (SOL), wakefulness after sleep onset (WASO), total sleep time (TST), sleep efficiency (SE) defined as the ratio of TST to total time spent in bed (TIB) and sleep perception index (SPI). Data will be collected through subjective entries in the sleep diary and objectively recorded by actigraphy (HUAWEI Smartwatch). Actigraphy can provide relatively accurate sleep parameter data while allowing for at-home monitoring. Its advantages include cost-effectiveness, convenience, portability and higher adherence, making it widely used in both clinical research and practice (63). Additionally, the actigraphy will analyze sleep states, including deep sleep, light sleep and rapid eye movement (REM) sleep. According to the research carried in Beth Israel Deaconess Medical Center in Harvard Medical School, the sleep states analyzed in HUAWEI Smartwatch achieved an accuracy of 79-92%, when the Electrocardiogram based Cardiopulmonary Coupling analysis (ECG-based CPC) was employed as true-event reference (64). Participants were required to keep daily sleep dairies and provide the actigraphy data during a 2-week baseline period, during the 8-week treatment and for 2 weeks prior to the scheduled follow-up assessment at 20 weeks, respectively. Sleep diaries will be recorded via smartphone and research assistants will send daily reminders via the smartphone to encourage participants to complete their entries on time. SPI is estimated using total sleep time (in hours) as perceived by the participants (via sleep diaries) divided by the total sleep time (in hours) measured by actigraphy (65).

Other measures include the motivation, frequency, duration and preference time of mindfulness practice in the MBCT-I group which is recorded during treatment and follow-up. Once the treatment is completed, we will investigate the intervention satisfaction of participants in both groups on arrangement, homework, leaders, atmosphere, effectiveness and technical difficulties. Medication use including changes in medication will be monitored in baseline, week 8 and week 20.

Retention rate (number and proportion that attended each class) of participants in MBCT-I group are documented. And reasons for non-attendance will be recorded. Participants who attended six or more iMBCT-I sessions will be considered as having completed the intervention. For those who did not complete the intervention, researchers would conduct interviews to inquire about the relevant reasons. In addition, the completion of the sleep diary, actigraphy usage, and the number of sessions attended are collected as indicators of adherence.

We will record the possible adverse events in detail during the intervention period, including the time of occurrence, duration, and treatment measures of the adverse events. Common adverse events of iMBCT-I may include anxiety, emotional or physical discomfort, sleep disruption and daytime sleepiness, and these possible conditions will relieve or disappear as the intervention progresses. Serious adverse events will be reported to the Tongji Hospital of Tongji University Institutional Review Board in a timely manner.

Changes between groups in ISI scores from baseline to week 8 will be evaluated using paired t-tests (for normally distributed data) or paired Mann-Whitney U tests (for non-normally distributed data). The between group effect sizes (Cohen’s d) will be calculated using the mean differences from baseline and the SDs of the two groups at week 8.

A Univariable linear regression will be conducted to evaluate the effect of MBCT-I on ISI score reduction. The change in ISI scores from baseline to week 8 will be used as the dependent variable, while the intervention group (MBCT-I vs. SHE) will be included as the independent categorical variable. The regression coefficient (B) will represent the estimated effect of MBCT-I on ISI score reduction.

To account for potential confounders, a multivariable linear regression analysis will be performed, adjusting for covariates including gender, age, marital status, educational background, and baseline ISI scores.

Changes between groups in scores of PSQI, FFMQ, PHQ-9, GAD-7, SF-12, ATSPPH-SF and DBAS-16, insomnia remission rate and all sleep parameters values from baseline to week 8 will be evaluated using paired t-tests (for normally distributed data)/Mann-Whitney U tests (for non-normally distributed data). Mixed-effect models for repeated measures will be used to evaluate the effects of the online MBCT-I on scores of ISI, PSQI, FFMQ, PHQ-9, GAD-7, SF-12, ATSPPH-SF and DBAS-16 as well as all sleep parameters values over time (from baseline to week 20). The model will include treatment group, time, treatment-by-time interaction and baseline covariates.

In order to identify predictors of effectiveness, subgroup analyses will be conducted to compare the efficacy of iMBCT-I among participants with different characteristics, such as demographics, mindfulness levels (FFMQ) and attitudes towards psychotherapy (ATSPPH-SF). Additionally, the relationship between the number of attended sessions and treatment efficacy will be explored using regression analysis, with session attendance as an independent variable and ISI score reduction as the dependent variable.

Structural equation models will be applied to identify possible mediators and moderators of intervention efficacy such as mindfulness levels (FFMQ) and attitudes towards psychotherapy (ATSPPH-SF) at baseline.