Subjective well-being has become a central issue in the development of public policy. In this context, there are concerns about the adequacy of current measures of economic performance, such as gross domestic product (GDP), to indicate societal well-being [1]. The Organisation of Economic Co-operation and Development (OECD) proposed that subjective well-being should be considered in addition to these objective scales as a complementary indicator of people’s well-being [2]. Following this initiative, several countries have launched challenges to propose a substitute indicator that complements GDP by measuring the progress of society [1,3-7].

Although arguments about the definition of subjective well-being are still in progress, the most widely accepted one is “good mental states, including all of the various evaluations, positive and negative, that people make of their lives, and the affective reactions of people to their experiences” [2]. There is a general consensus among experts that subjective well-being consists of at least two aspects: life evaluation and affect. In addition, several researchers have insisted that the eudemonic aspect, reflecting people’s sense of purpose and engagement, should also be included in subjective well-being [8]. Thus, subjective well-being consists of three dimensions: life evaluation, affect, and eudemonia.

The importance of subjective well-being is not limited to economics. Several studies have indicated that subjective well-being affects the health of the general public. Steptoe et al revealed that impairment of subjective well-being by depression and life stress elevates the risk of premature death [9]. In addition, higher eudemonic well-being may work as a protective factor for health [10-12]. Therefore, improving the subjective well-being of the general public is significant from a public health perspective.

Several interventions, such as a positive events diary [13], life coaching and attainment of goals [14], and positive future thinking [15], have proven effective in the improvement of subjective well-being for nonclinical populations. Furthermore, mindfulness-based intervention (MBI) is another measure that potentially improves people’s subjective well-being. Although MBI was originally developed for the treatment of clinical populations, such as patients with chronic pain [16], depression [17], or anxiety disorders [18], its scope has recently expanded to nonclinical populations. Some studies have already shown its effects on decreasing stress and improving subjective well-being [19-30].

The studies discussed above, however, have several limitations. First, because they tended to target specific populations, such as students [20,22,26,28,29], schoolteachers [21,23], health care professionals [19,27], and workers in the workplace [31-34], the generalizability of the results to the community is limited. Second, although two studies targeted healthy individuals in the community [24,25], they assessed either the life evaluation or affective aspect of subjective well-being rather than all three aspects (ie, cognitive, affective, and eudemonic aspects). Thus, no study has evaluated the eudemonic aspect of well-being, which has been proven to have a relationship with health [35]. Finally, although the effect of mindfulness-based stress reduction (MBSR) on subjective well-being has been evaluated, no study has assessed the effect of mindfulness-based cognitive therapy (MBCT) [36], which is the other major MBI currently practiced. Therefore, we decided to conduct a randomized controlled trial to demonstrate MBCT’s effectiveness on three different aspects of subjective well-being (ie, life evaluation, affect, and eudemonia) for healthy individuals sampled from community residents.

The primary objective of this study is to investigate the effectiveness and cost-effectiveness of MBCT for improving the subjective well-being of healthy individuals in a randomized, wait-list, and controlled trial.

The study is being conducted at Keio University Hospital in Tokyo, Japan. Participants will be recruited through the Center for Stress Research at Keio University (Keio CSR). Eligible participants are people (1) between the ages of 20 and 65 years, (2) without a history of psychiatric disorders or who have been recovered from psychiatric disorders for more than 2 years, (3) with scores lower than 25 on the Satisfaction With Life Scale (SWLS), and (4) who can provide written informed consent.

Participants will be excluded if they (1) are difficult to follow up with 4 months after the start of the intervention, (2) have a past history of MBIs equivalent to the program provided in the study, and (3) have severe physical conditions.

Prospective participants who apply to the study through the form at the Keio CSR’s website will be asked to fill out screening questionnaires via the Web (ie, the first screening). If the participants pass the first screening, they will meet a member of the study team who will conduct a face-to-face interview (ie, the second screening) to establish if they meet the inclusion criteria. The Japanese version of the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), Axis I Disorders [37], will be used for diagnostic assessment. The first, second, and third authors (MS, TK, and AN) will conduct the second screening. The eligibility of the participants will be judged based on the results of this second screening. All participants will provide written informed consent after receiving a detailed explanation of all the procedures and will be able to withdraw their consent at any time without negative consequences.

Eligible participants will be randomly assigned, at a 1:1 ratio, to the MBCT group or the wait-list control group. A computer-generated random number stratified by the baseline score of the SWLS will be allocated to each participant. The Keio Center of Clinical Research Project Management Office, which is not associated with this study, will manage the process of the randomization. The flow diagram of the study participants is shown in Figure 1.

Due to the nature of this psychological intervention, the randomization status of participants and program instructors cannot be blinded. Because all measures obtained through the study period are self-reported, there will be no assessors to judge the state of participants.

Cost-effectiveness will be assessed based on the incremental cost-effectiveness ratio that represents the incremental cost divided by the incremental effectiveness between the groups. With respect to cost, we only include the human resource cost to deliver the sessions, since the study targets healthy individuals. Because the population targeted in the study is composed of healthy individuals, incremental effectiveness will be evaluated primarily using the measures of subjective well-being, such as the SWLS. However, we will also use the quality-adjusted life years mapped from the results of the EQ-5D-5L and so on, representing health-related quality of life as the secondary incremental effectiveness outcome. The analyses will be conducted from a third-party payers’ perspective.

All participants will be asked to complete these psychological self-reporting measures at 4 weeks (ie, the intervention midpoint), 8 weeks (ie, postintervention), and 2 months (ie, 16 weeks) after the completion of the intervention, as well as at their baseline assessments (ie, week 0). The assessment schedule is shown in Table 2.

We performed sample size calculation based on the results of a previous feasibility study that we had conducted, which assessed the feasibility, safety, and effectiveness of MBCT for improving subjective well-being with a single arm. The pre-post difference in the mean score of the SWLS in the study was 3.1 (SD 3.4). With a statistical power of at least 80% and a two-sided 5% significance level, the sample size was calculated to be 20 participants for each arm. Allowing for a dropout rate of approximately 20%, we determined that each arm would need 25 participants, for a total of 50 participants.

A 5% significance level will be used for all statistical analyses. To compare differences in the baseline demographics and clinical characteristics of the two groups, unpaired t tests will be used for the continuous variables and chi-square tests for the categorical variables. The primary and secondary outcomes will be analyzed using an intent-to-treat approach and a mixed-effect model repeat measurement, a method of handling dropouts in longitudinal clinical trials. Stata 14 (StataCorp) will be used to carry out statistical analysis.

When we notice serious adverse events, we will report them to the Ethics Review Committee of the Keio University School of Medicine.

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 participants and patients were approved by the Ethics Review Committee of the Keio University School of Medicine (reference number: 20170258). The study has been registered in the University Hospital Medical Information Network (UMIN) Clinical Trials Registry (UMIN 000031885).

The results of the study will be disseminated at several academic conferences and as published articles in peer-reviewed journals. The study will be implemented and reported in line with the CONSORT (Consolidated Standards Of Reporting Trials) statement.

The datasets are available from the corresponding author upon reasonable request.