A total of 5 studies [22-25,38] involving 690 university students assessed stress as the outcome. Among the 5 studies, 4 [22-24,38] used the Perceived Stress Scale (PSS) [41], and 1 [25] used the 21-item Depression, Anxiety, and Stress Scale (DASS-21) [42]. Owing to the different measurement tools used in the studies, SMD was chosen for the meta-analysis. A fixed-effect model was selected for the statistical analysis, as low heterogeneity was observed between the studies (I²=39%, P=.16). It was found that stress decreased significantly in the experimental group (SMD –0.41, 95% CI –0.59 to –0.23; P<.001) compared with that in the control group (Figure 4).

A total of 4 studies [25,26,38,40] involving 617 university students assessed anxiety as the outcome. Among the 4 studies, 3 [26,38,40] used the State-Trait Anxiety Inventory (STAI) [43], and 1 [25] used the DASS-21 [42]. SMD was chosen owing to the different types of measurement tools used in the studies. A fixed-effect model was selected for the statistical analysis, as low heterogeneity was observed between the studies (I²=37%, P=.19). It was found that anxiety decreased significantly in the experimental group (SMD –0.29, 95% CI –0.50 to –0.09; P=.004) compared with that in the control group (Figure 5).

A total of 5 studies [22,25,27,38,40] involving 556 university students assessed depression. Among the 5 studies, 2 [27,40] used the 9-item Patient Health Questionnaire (PHQ-9) [44] and the other 3 [22,25,38] used the Center for Epidemiological Studies’ Depression Scale (CES-D) [45], the Quick Inventory of Depressive Symptomatology Self-Report (QIDS-SR) [46], and the DASS-21 [42] separately. Owing to the different measurement tools used in the studies, SMD was chosen for the meta-analysis. No statistical significance was found between the experimental and control groups (SMD –0.14, 95% CI –0.30 to 0.03; P=.11). Moreover, significant heterogeneity (I²=72%, P=.006) was observed between the 5 studies. Sensitivity analysis was performed on the outcome, but no individual study was found to qualitatively affect the results. Subgroup analysis was conducted to determine the differences between the studies. The use of either waitlist control or traditional face-to-face intervention in the control group was identified as the source of heterogeneity: specifically, the waitlist control subgroup (SMD –0.33, 95% CI –0.53 to –0.13; P=.002) versus the face-to-face subgroup (SMD 0.29, 95% CI –0.01 to 0.59; P=.06). The results showed that the effects of MMM and traditional face-to-face mindfulness meditation on depression were similar (Figure 6).

Four studies [22,24,39,40] involving 400 university students assessed anxiety as the outcome. Among the 4 studies, 2 [39,40] used the Warwick-Edinburgh Mental Well-Being Scale (WEMWBS) [47], and the remaining 2 [22,24] used the WHO-Five Well-Being Index (WHO-5) [48] and the General Well-being Schedule (GWBS) [49]. SMD was chosen owing to different types of measurement tools used in the studies. A fixed-effect model was selected for the statistical analysis, as small heterogeneity among studies was observed between the studies (I²=25%, P=.26). It was found that well-being increased significantly in the experimental group (SMD 0.30, 95% CI 0.11-0.50; P=.003) compared with the control group (Figure 7).

Four studies [23,24,26,27] involving 348 university students assessed mindfulness. All 4 studies used the Five Factor Mindfulness Questionnaire (FFMQ) [50]. Mean difference was chosen for the meta-analysis, and it was found that mindfulness increased significantly in the experimental group (SMD 2.66, 95% CI 0.77-4.55; P=.006) compared with the control group. However, significant heterogeneity (I²=88%, P<.001) was observed between the 4 studies. Sensitivity analysis was performed on the outcome, but no individual study was found to qualitatively affect the results. Subgroup analysis was conducted to determine the differences between the studies. Support from a company may be the source of the heterogeneity, specifically the “without company support” subgroup (SMD 17.60, 95% CI 11.32-23.87; P<.001) versus the “with company support” subgroup (SMD 1.17, 95% CI –0.82 to 3.15; P=.25). The results showed that MMM without company support significantly improved mindfulness (P<.001; Figure 8).

A total of 3 studies [22,27,37] involving 302 university students assessed resilience as the outcome. Two studies [27,37] used the Wagnild Resilience Scale (WRS) [51] and 1 [22] used the Connor-Davidson Resilience Scale (CD-RISC) [52]. SMD was selected owing to different types of measurement tools used in the studies. A fixed-effect model was selected for the statistical analysis, as low heterogeneity was observed between the studies (I²=12%, P=.32). No statistical significance was found between the experimental group and the control group (SMD –0.06, 95% CI –0.26 to 0.15; P=.59; Figure 9).

The results showed that the quality of evidence ranged from moderate to low. The between-rater κ coefficient was 100% (P=.001), indicating perfect between-rater agreement during the evaluation process. The quality of the evidence is summarized in Table 2.

The primary outcome of our study was the effectiveness of MMM in reducing stress, anxiety, and depression among university students. These 3 psychological problems were reported as significant factors influencing students’ academic performance and physical health, such as back pains, headaches, and irritable bowel syndrome [54]. Thus, developing effective mental health management strategies to address the aforementioned psychological issues is essential [23].

Stress is an individuals’ natural reflection in the face of tension, which may lead to worry, restlessness, among others [55]. This study showed a significant reduction in stress among university students in the MMM intervention group (SMD –0.41, 95% CI –0.59 to –0.23; P<.001), which is similar to the findings of previous studies [22,23,56]. Possible reasons for this outcome exist. For example, previous studies proved the positive effectiveness of traditional mindfulness therapy in reducing stress among university students [57,58]. Mindfulness meditation through smartphone apps may improve muscle relaxation and diaphragm breathing, focus attention on different parts of the body, raise noncritical awareness of events occurring continuously, and enhance self-reflection [59]. In addition, MMM requires less resources (in terms of cost, personnel, or buildings), as it can be easily accessed through smartphones, regardless of economic and other constraints [60]. In particular, MMM involves minimal time and space constraints, as university students can just turn on their smartphones to receive mindfulness treatment anytime and anywhere at their convenience, instead of setting a fixed time and place for unified concentration, such as in traditional methods. Such advantages can help students obtain increased and convenient treatment, which may be a highly practical way to reduce stress [23].

Anxiety refers to an unpleasant complex emotional state, such as tension, uneasiness, and worry, caused by imminent or possible danger or threat [61]. This study revealed that university students in the experimental group were able to lower their anxiety level compared with those in the control group (SMD –0.29, 95% CI –0.50 to –0.09; P=.004), which is consistent with previous findings [40,58]. The possible causes were analyzed as follows: university students often feel stigmatized when they reveal having mental issues, and may be reluctant to seek treatment in the school hospital or psychological counseling center from fear of being seen by classmates or teachers, who may label them as having mental health problems, which can further aggravate their anxiety and other problems [62]. Through mobile devices, students can receive treatment remotely, thus avoiding the embarrassment of face-to-face contact [38]. Intervention through mobile devices may have several advantages, such as usefulness, convenience, and ease of use; additionally, it is more popular among and easily accepted by university students [63]. This improved engagement and accessibility in anxious individuals who may prefer apps to face-to-face group mindfulness programs. Interestingly, a previous study reported that smartphone-aided psychological treatments can decrease anxiety among users [64], which may be another reason for the outcomes.

The main clinical characteristics of depression are manifested mainly as depressed moods, slow thinking, reduced language and movement, and retardation [65]. This study showed no statistical difference in depression between university students in the experimental group and those in the control group. Heterogeneity was detected between the studies (I²=72%, P=.006), whereas the sensitivity analysis indicated that no single study qualitatively affected the combined results. Subgroup analysis was performed to identify the potential causes of the heterogeneity. For the experimental design process, in the case of similar interventions in the experimental group, 3 of the 5 studies set the control group as a waitlist control, and the other 2 studies used traditional face-to-face mindfulness meditation. Thus, it can be concluded that the “face-to-face mindfulness meditation” group (SMD 0.29, 95% CI –0.01 to 0.59; P=.06) was superior to the “waitlist control” group (SMD –0.33, 95% CI –0.53 to –0.13; P=.002) in terms of reduced symptoms of depression. This result is in line with previous findings [25,27]. A reason for this outcome maybe that MMM and traditional mindfulness meditation methods can effectively alleviate the depressive symptoms of university students and have the same effect size [25,27]; thus, no significant difference was observed between the MMM and traditional intervention control groups. Meanwhile, no intervention measures were used in the waitlist control group; thus, the depressive symptoms of university students in this group did not change significantly [22]. Therefore, a significant difference existed between the experimental and control groups.

The secondary outcome of our study was the effectiveness of MMM in increasing well-being, mindfulness, and resilience among university students. The 3 outcomes had a close positive correlation with mental health [66]. Improving well-being, mindfulness, and resilience can help university students to effectively deal with mental distress, such as stress, anxiety, and depression [67].

Well-being refers to a series of joyful emotions subjectively generated by individuals based on their sense of satisfaction and security [68]. Compared with university students in the control group, MMM may strengthen the well-being of those in the experimental group (SMD 0.30, 95% CI 0.11-0.50; P=.003), which is in line with the findings of previous studies [22,24]. A possible reason is that the advantage of the MMM intervention is the rigorous smartphone intervention, because the standardized guidance scheme and objective compliance measures of the participants in the experimental group were provided by apps; thus, the intervention method was homogeneous [1]. Likewise, a recent meta-analysis showed that 67% of positive psychological interventions are conducted in the form of self-help. This form is similar to the advantage offered by MMM based on smartphone apps, as university students could choose an intervention performed based on their needs [69]. Smartphone-based self-intervention programs allow university students to avoid certain risks and restrictions related to traditional methods, such as time, resource, flexibility, accessibility, and availability constraints [70]. Such programs also meet the requirements of the WHO, especially the use of electronic and mobile health technologies [71].

Mindfulness is perceived in a specific way, that is, conscious awareness, living in the present, and not making judgments [72]. Our study revealed a significant improvement in the mindfulness of university students in the MMM intervention group. Heterogeneity was detected between the studies (I²=88%, P<.001), and the sensitivity analysis suggested that no single study qualitatively affected the combined results. Subgroup analysis was performed to identify the potential causes of the heterogeneity. In the design process, 2 of the 4 studies were funded or technically guided by professional companies, whereas the other 2 did not obtain business funding or guidance. Thus, it can be concluded that the “without company support” group (SMD 17.60, 95% CI 11.32-23.87; P<.001) was superior to the “with company support” group (SMD 1.17, 95% CI –0.82 to 3.15; P=.25) in raising the level of mindfulness. This result is in line with previous findings [23,26]. Besides, the results of the studies funded or technically guided by companies may have risks of bias [33]. Thus, caution should be exercised when interpreting such findings. Research supports this study’s idea that a significant advantage of MMM is the objective recording of the number of meditation sessions completed by university students by an app instead of self-reporting [73].

Changes in psychological resilience among university students were also observed. Resilience refers to an individuals’ ability to recover from negative experiences and adapt flexibly to the changing external environment [74]. The results indicated no statistical difference between the 2 groups (SMD –0.06, 95% CI –0.26 to 0.15; P=.59), which are in line with those of previous studies [22,27,37]. A possible reason for this outcome may be that resilience-based interventions emphasize individuals’ and community members’ strength and ability to recover from physical, emotional, or environment stress [75]. A positive correlation was observed between psychological resilience and education level [76]. University students have a high education level; therefore, it was assumed in this study that university students had high psychological resilience before seeking the MMM intervention.