Mindfulness has been practiced for centuries in the context of Buddhism and contemplative Christianity [1,2]. Nonetheless, research in this area has only flourished globally over the last two decades [3,4]. According to Kabat-Zinn [5], mindfulness refers to the awareness arising frompaying attention nonjudgmentally to present-moment experiences such as emotions, thoughts, and body sensations. Numerous studies have shown that mindfulness has health benefits including better quality of life, better sleep quality, lower stress, less anxiety and depressive symptoms [6–9], and greater life satisfaction [10,11]. In addition, mindfulness also fosters greater spirituality. For instance, a meta-analytic study showed that after attending interventions such as mindfulness-based cognitive therapy (MBCT; [12]) and mindfulness-based cancer recovery (MBCR; [13]), participants from diverse clinical and nonclinical samples experienced greater spirituality [14]. As such, studies to date have shown that mindfulness is broadly linked to better spirituality, health, and well-being.

According to Pesut [15], spirituality has two dimensions including a relationship to a supreme being or God, as well as intrapersonal and interpersonal connectedness. Kreitzer et al. [16] further explained that spirituality overarches multiple components including serenity, which is defined as the spiritual state of inner peace, regardless of the experience of positive and negative life events [16–18]. More specifically, serenity is a three sub-dimensional construct including acceptance of self and uncontrollable events, ability to tap into the inner haven of peace, and trust in the meaningfulness and profoundness of life [16]. As such, serenity highlights individuals’ connectedness within the self, to other people, and to nature, which are crucial for well-being and mental health [16]. Previous research indicated that greater mindfulness was linked to greater internal peace and harmony [19,20]. After attending mindfulness-based programs, such as the MBSR [21], health care practitioners reported increased serenity [22–24]. Importantly, Shapiro et al. [25] theorized that mindfulness practice enables a shift of perspectives that foster an accepting attitude toward negative emotions, an ability to enter the space of inner calmness, and a recognition of meaningful values, all of which point to greater serenity. Individuals who are more mindful are also more able to experience intense emotions with less reactivity and more objectivity. That is, mindfulness enables individuals to remain calm and non-reactive, despite an awareness of strong emotions [16,18]. Previous research suggested that the stability of inner peace brought by spirituality was related to positive well-being outcomes, including fewer depressive symptoms and greater life satisfaction [26–28]. Other studies differentially indicated various aspects of serenity (e.g., acceptance of self and events beyond one’s control, inner peace, and faith in the meaningfulness of life and larger plan) as mediators between mindfulness and well-being outcomes [19,29,30]. As a unifying construct, serenity may serve as a mediator between mindfulness facets and well-being outcomes, including depressive symptoms and life satisfaction.

The Five Facets Mindfulness Questionnaire (FFMQ; [31]) is commonly used to measure mindfulness. It encompasses facets including observing, nonjudging of inner experience, describing, acting with awareness, and nonreacting to inner experience. According to Baer et al. [32], observing refers to attending to or noticing experiences internally and externally, namely sounds, emotions, and thoughts. Nonjudging of inner experience refers to adopting a nonevaluative position towards inner experiences, such as feelings and thoughts. Describing involves the labeling of inner experiences using words. Acting with awareness refers to attending to present-moment activities rather than being on autopilot. Finally, nonreacting to inner experience involves the inclination to let inner experiences (e.g., thoughts and feelings) come and go, instead of being taken away by them.

Although the longstanding literature has identified the positive associations between mindfulness and well-being outcomes [8–10], emerging studies have highlighted differential contributions of each mindfulness facet on psychological well-being [33–36]. For example, a study found that contradictory to other facets, observing was positively associated with psychological distress [33]. The authors speculated that the greater tendency to observe experiences may lead to anxiety or panic, particularly if the experiences are perceived as negative or dangerous. Another study suggested that observing may be indicative of maladaptive self-attention, which may impede nonjudgmental moment-to-moment awareness and give rise to greater distress [36]. Furthermore, a study involving a nonclinical sample indicated that after controlling for age, gender, and meditation practices, observing and describing did not predict psychological distress, whereas the other three facets of mindfulness, including nonjudging, nonreacting, and acting with awareness, were significant predictors of distress [33]. Baer [37] posited that for individuals without an experience of meditation, observation and attention to the present moment may be impulsive and judgmental. On the contrary, mindfulness practices may enable meditators to observe openly and acceptingly [37]. Therefore, observing may be positively related to well-being outcomes among meditators. However, a study reported that observing was related to greater rumination and lower attentional control, and that the indirect effects of observing on mental and physical health complaints via greater body awareness and nonattachment were significant among samples with or without meditation experience [38]. As such, the association between observing and well-being among meditators and non-meditators remains inconsistent and unclear. As for the other mindfulness facets, Bergin and Pakenham [33] reported positive relations between all facets of mindfulness and life satisfaction, except for nonreacting. Given the inconsistency and scarcity of the findings especially among regular meditators, it is crucial to examine the unique contribution of each mindfulness facet to psychological well-being.

Guided by Shapiro et al.’s [25] theory on mindfulness, the present study investigated serenity as a mediator between mindfulness facets and well-being outcomes, including depressive symptoms and life satisfaction, among mindfulness practitioners. Of note, a majority of studies in this area involved samples from the community, university or clinical settings [27,28,30,39,40]. Relatively few studies have examined the role of mindfulness on mental health among meditators, particularly in diverse Chinese contexts. Among the studies conducted in the Chinese context, findings did show that dispositional mindfulness was linked to depression and life satisfaction [6,10,41] and that an aspect of serenity (i.e., self-acceptance) did mediate the association between mindfulness and mental health among emerging adults between 17 and 25 years of age in Hong Kong [26]. Nevertheless, more work is needed to understand the role of the unifying construct of serenity encompassing inner haven of peace, acceptance of self and uncontrollable events, and trust in the meaningfulness and profoundness of life.

Based on theory [25], the present study hypothesized that serenity would mediate the association between mindfulness facets and psychological well-being, including depressive symptoms and life satisfaction, among Chinese mindfulness practitioners. Importantly, facets of mindfulness including nonjudging and nonreacting to inner experience, noticing and describing inner experience with clarity, and being aware of and attending to the present moment were expected to foster psychological functioning, including serenity. However, previous studies did reveal mixed findings between mindfulness facets such as observing and psychological distress [33,36,37], depending on people’s experience of meditation [37]. Notably, as meditators were likely to observe their inner experience open-mindedly with curiosity, they might report better psychological functioning, including serenity and mental health. To understand the effect of meditation experience, supplementary analyses were conducted. Specifically, we tested a moderated mediation model, with hours of meditation per week as a moderator between mindfulness facets and psychological functioning, including serenity, depressive symptoms, and life satisfaction.

Table 2 shows the correlations, means, and SDs of the variables. Given that the correlations between the subscales of serenity were high, with rs ranging from 0.70 to 0.90, ps < 0.001 (see Table 2), a latent variable of serenity was formed. The structural model fit adequately to the data, χ²(279) = 384.79, p < 0.001, CFI = 0.94, TLI = 0.93, RMSEA = 0.06; SRMR = 0.06 (see Table 3 and Fig. 1 for details). Latent variables including serenity, depressive symptoms, and life satisfaction were significantly indicated by their respective manifest indicators, ps < 0.001. After controlling for age, gender, income, years of education, meditation experience, and hours of meditation per week, two facets of mindfulness including describing and nonreacting were positively associated with serenity (B = 0.16, SE = 0.06, β = 0.18, p = 0.009 and B = 0.59, SE = 0.06, β = 0.71, p < 0.001, respectively). Serenity was, in turn, negatively related to depressive symptoms (B = −0.40, SE = 0.19, β = −0.40, p = 0.036) and positively related to life satisfaction (B = 1.98, SE = 0.34, β = 1.03, p < 0.001). In addition, two other facets of mindfulness were associated with depressive symptoms. Specifically, observing was positively related to depressive symptoms (B = 0.21, SE = 0.07, β = 0.28, p = 0.004), whereas nonjudging was negatively related to depressive symptoms (B = −0.23, SE = 0.07, β = −0.26, p = 0.001).

Based on the above findings, the indirect effects between two facets of mindfulness, including describing and nonreacting, and depressive symptoms and life satisfaction through serenity were investigated. Based on 5000 bootstrap samples with replacement, the 95% confidence interval (CI) indicated that the unstandardized indirect effect between describing and depressive symptoms did not include a zero (CI: [−0.21, −0.001]). However, the 95% CI indicated that the unstandardized indirect effect between nonreacting and depressive symptoms included a zero (CI: [−0.56, 0.04]). As for life satisfaction, based on 5000 bootstrap samples with replacement, the 95% confidence interval (CI) indicated that the unstandardized indirect effect between describing and life satisfaction did not include a zero (CI: [0.06, 0.36]). In addition, the 95% CI indicated that the unstandardized indirect effect between nonreacting and life satisfaction did not include a zero (CI: [0.46, 1.11]). Hence, serenity mediated between describing and life satisfaction. Serenity also mediated between two facets of mindfulness, including describing and nonreacting, and life satisfaction.

Supplementary analysis was further conducted by examining the moderation effects of hours of meditation practice per week on the relation between mindfulness facets and well-being (i.e., depressive symptoms and life satisfaction), with serenity as a mediator. More specifically, the interaction terms were computed by centering and multiplying each facet of mindfulness and hours of meditation practice per week. To conduct the moderated mediation analysis, mindfulness facets, hours of meditation practice per week, and the interaction terms were entered as predictors of serenity, depressive symptoms, and life satisfaction. Findings revealed that the moderated mediation model did not fit adequately to the data, χ²(360) = 838.07, p < 0.001, CFI = 0.68, TLI = 0.63, RMSEA = 0.11; SRMR = 0.23. As such, the moderated mediation model was not supported.

Guided by Shapiro et al.’s [25] theory on mindfulness, this study examined serenity as a mediating process between mindfulness facets and psychological outcomes. The present findings provided incremental support to suggest serenity as a mediator between two facets of mindfulness [31], namely describing and nonreacting to inner experience, and life satisfaction. Serenity also mediated the relation between describing and depressive symptoms. In addition, direct associations were evidenced between mindfulness facets (i.e., observing and nonjudging of inner experience) and depressive symptoms. Altogether, the findings revealed mindfulness facets as major correlates of serenity and psychological outcomes among Chinese mindfulness practitioners, over and above the effects of age, gender, education, household income, experience of meditation, as well as hours of meditation each week.

In this study, serenity was associated with mindfulness facets (i.e., describing and nonreacting to inner experience) and psychological well-being. When people were capable of describing clearly and responding skillfully (vs. reacting mindlessly) to their experiences, they were also more likely to have greater serenity, e.g., accept themselves and uncontrollable events, touch the inner haven of peace, and trust that life is meaningful and profound [16]. Between the two mindfulness facets, the strength of association between nonreacting to inner experience and serenity was particularly strong, suggesting that the ability to pause, to “step back” without being taken over by inner experience, and to let go were especially crucial to shifting perspectives that foster serenity (see also [25]). Hence, to promote serenity, researchers, educators, and mindfulness practitioners should pay close attention to the role of nonreacting to inner experience.

Somewhat surprisingly, other facets of mindfulness including observing, nonjudging of inner experience, and acting with awareness were unrelated to the spiritual state of serenity. Even though the mindfulness facets were intercorrelated, their relations with serenity did not bear out after describing and nonreacting to inner experience were taken into account. Nonjudging of inner experience and observing were, instead, directly related to depressive symptoms, a core indicator of mental health. Consistent with previous research [34,51,52], when people were more judgmental and critical of their inner experience (e.g., “my thoughts are good, bad, or inappropriate”) and of how they should be (e.g., “I shouldn’t feel this way”), they were more likely to have greater depressive symptoms. Nevertheless, when people were more observant of their experiences internally and externally, they were also more likely to have greater depressive symptoms. The findings corroborated previous research [33,36] to suggest that observing was positively related to depressive symptoms. As speculated by Tran et al. [36], perhaps observing was indicative of maladaptive self-attention that gave rise to depressive symptoms. Although Baer [37] argued that people without meditation experiences might observe the present judgmentally and impulsively, whereas practitioners might observe with openness and acceptance, in this study we found a positive link between observing and depressive symptoms among practitioners with a regular meditation practice (See [53] and [38] for similar findings). In addition, our SEM findings revealed that observing was not related to nonjudging of inner experience at all (see Fig. 1). Given that observing was moderately related to describing (r = 0.57, p < 0.001) and nonreacting to inner experience (r = 0.44, p < 0.001), the finding between observing and depressive symptoms could also be the result of multicollinearity. Hence, the study of observing and depression among people with and without meditation experience warrants future investigation.

Interestingly, acting with awareness was not related to serenity, depressive symptoms, or life satisfaction. That is, the ability to pay attention without distractions, daydreaming, or worrying was not related to serenity and psychological functioning, particularly when other mindfulness facets were taken into account. The null finding was intriguing, as it diverged from existing findings between mindful attention awareness [54], mind wandering, and psychological well-being [55,56]. It also contradicted previous findings between mindful awareness and serenity based on samples from the Western contexts [16,28]. Given that our participants were meditators, it is possible that advanced mindfulness skills, such as nonreacting and nonjudging [57], had a stronger effect on psychological functioning. This might overshadow the effect of acting with awareness, which is a fundamental mindfulness skill that involves the arising awareness from paying attention to the present moment. To fully understand the link between acting with awareness and serenity, or the lack thereof, researchers should pay a closer attention to the use of assessments (e.g., FFMQ; [31] vs. Mindfulness Attention and Awareness Scale, MAAS; [54]), the role of culture (e.g., collectivistic vs. individualistic cultures), and sample characteristics (e.g., people with and without experiences of meditation, clinical samples, non-clinical samples).

Although Baer [37] argued that the effects of mindfulness facets could differ between meditators and non-meditators, in this study the hours of meditation per week did not moderate the associations between mindfulness and psychological functioning. Given that all of our participants practiced meditation, perhaps the hours of meditation were not the most crucial in changing the relation between mindfulness and psychological functioning. Alternatively, it could be that the statistical power of this study was insufficient to draw meaningful conclusions on the moderated mediation model. As such, future studies should include a larger sample for conducting complex moderated mediation analyses.

Consistent with previous findings [16,28], the core aspects of serenity were related to both depressive symptoms and life satisfaction. These findings suggested an important link between spiritual health and psychological well-being. In addition, serenity served as a potential mechanism between the mindfulness facets of describing and nonreacting to inner experience and psychological well-being. Supporting the literature, the findings inform researchers, educators, and mindfulness and mental health practitioners of the relevance of being mindful and serene in mental health.

The present study has several limitations. First of all, the utilization of a self-report questionnaire had resulted in method bias [58]. Thus, future studies should include multiple methods and multiple informants to reduce potential biases. Second, due to the cross-sectional design of the present study, we were unable to draw conclusions on the temporal sequence between the study variables. Future research should utilize a longitudinal design in testing mediation [59]. Third, although nonreacting to inner experience and aspects of serenity are theoretically distinct variables, their zero-order correlations were large [60], ranging between rs = 0.70 and 0.84 (see Table 2). According to Baer et al. [32 p. 330], nonreacting to inner experience refers to “the tendency to allow thoughts and feelings to come and go, without getting caught up in or carried away by them.” As an overarching construct, serenity refers to the spiritual state of inner peace, regardless of the experience of positive and negative life events [16]. Although both constructs suggest nonreactivity to experiences, the mindfulness facet of nonreacting points primarily to inner experiences (e.g., thoughts, and feelings), whereas serenity involves spiritual states regardless of internal vs. external experiences or stimuli. Serenity further involves an added layer of peace, trust, and acceptance beyond nonreactivity. Despite the potential differences, future research should distinguish or clarify theoretically and empirically the relation between non-reactivity and serenity. Moreover, the participants in this study were self-reported meditators with an average practice of 2.98 years (SD = 4.13 years). As such, the generalizability of the present findings to other samples was limited. Future studies should replicate the present findings in diverse samples, such as clinical samples, community samples, and samples from diverse cultural contexts. Next, given the theoretical considerations [16] and the strong correlations between the subscales of serenity (See Table 2), serenity was examined as a latent construct. However, serenity subscales including inner haven of peace, acceptance of self and uncontrollable events, and trust in the meaningfulness and profoundness of life may be differentiated across different cultural contexts. Hence, future studies may recruit a larger sample to further examine the unique relations between dimensions of mindfulness and serenity, respectively. Moreover, given previous research found significant associations between mindfulness, life satisfaction, and depressive symptoms [61–64], the present study aimed to replicate the findings and examine the incremental value of serenity. Nevertheless, other variables of psychological well-being such as anxiety, perceived stress, self-regulation, emotional stability, and self-esteem might also be linked to mindfulness and serenity. As such, future studies should examine a wide range of psychological outcomes to add generalizability and specificity to the present findings. Finally, in this study, the recruitment of mindfulness practitioners took place in a meditation event and most of the study participants were women. Hence, future work is necessary to increase generalizability.

Despite the above limitations, the present study lends preliminary support to Shapiro et al.’s [25] theory on mindfulness and broadens the literature involving serenity as a process between mindfulness facets and psychological outcomes. As practical implications, educators and mental health practitioners should attend to the relations between various facets of mindfulness, serenity, and mental health. Notably, describing and nonreacting to inner experience may foster serenity, which is linked to well-being outcomes including better life satisfaction and fewer depressive symptoms. In terms of research implications, theoretical and empirical studies are necessary to clarify why, how, and when mindfulness facets are linked to serenity and mental health. Translational research gearing towards enhancing mindfulness and serenity also merits future investigations.