The WHO reported that about 8% of the world's population has an emotional disorder (e.g., depression or anxiety), which is one of the leading causes of disability and mortality (1). Patients with emotional disorders often have adverse psychological and physiological effects at the same time, which not only threaten personal health and reduce the quality of life, but also burden families and society (2, 3). At present, the main treatment methods for patients with emotional disorders are psychotherapy and drug therapy. However, clinical drug treatment causes different side effects in patients, along with a high cost of treatment and limited treatment effectiveness (2). Research has shown that, through the development of appropriate mental health projects and plans, early prevention and screening can effectively prevent these mental health problems (2). However, if emotional symptoms are not regulated through intervention, there will be even more negative emotional consequences or they can develop into depression, anxiety, and other emotional disorders (4, 5). Hence, prevention (instead of intervention) among the non-clinical population with emotional symptoms is of great importance.

Mindfulness is an awareness that emerges through a conscious, present, and uncritical way of focusing on the experience that is present from moment to moment (6, 7). Its benefits include enhancing consciousness, strengthening self-regulation, strengthening openness and acceptance of current experience, and looking at problems from different perspectives (6, 7). At present, mindfulness-based interventions include the Buddhist tradition of Vipassana and Zen, which are now standardized group meditation exercises (e.g., mindfulness decompression and mindfulness-based cognitive therapy), and mindfulness-based psychological intervention [e.g., dialectical behavior therapy and Acceptance and Commitment Therapy (ACT)] (8). A large number of studies have confirmed that mindfulness therapy has a strong psychological impact on clinical and non-clinical populations, such as increased attention, reduced stress, less anxiety, and fewer negative emotions (9–12). Therefore, mindfulness therapy is an effective intervention for traditional medicine and psychotherapy globally (2). However, traditional mindfulness exercise takes a long time, learning costs are high, and teachers are relatively scarce. Moreover, effective mindfulness delivery media have been shown not only to assist in face-to-face mindfulness intervention but also to help those who cannot actively seek professional help or are prone to discontinue treatment for some reason (13, 14).

With the continuous development of health-related smartphone apps or smartphones, this emerging field is increasingly becoming a trend. People regularly use smartphones to acquire health knowledge or seek more healthy methods of living from the smartphone, which has enabled people to think about whether it is possible to combine apps in smartphones with psychological research (8). At present, intervention measures based on smartphone apps may further break the space-time limitation of training, improve training motivation, and broaden application prospects (15). Mani et al. (14) evaluated 23 apps in the apple app store found some smartphone apps that specialize in mindfulness intervention have a sharing function or provide access to an app community directly within the app, which can help users share and discuss their mindfulness experiences and challenges in routine exercises, motivate users to participate in health activities, and improve users' mental health level and wellbeing (14). Moreover, the unlimited time and place characteristics of these apps can meet the needs of modern people, which can not only assist in face-to-face mindfulness intervention but can also help those who are unable to seek professional help actively or who are prone to discontinue treatment for some reason, especially young people who enjoy their smartphones but lack the willingness to actively ask for help. Thus, choosing as smartphone app for mindfulness training is the right choice for many people. Studies have shown that electronic health intervention based on mindfulness and relaxation has a positive impact on the physical and mental health of patients with diseases (16). Another study found that mindfulness exercise guided by a smartphone app had a positive effect on relaxing and distracting children with chronic diseases (17). In addition, mindfulness intervention based on network and smartphone device media has been proven effective in reducing stress (18). The above findings indicate that mindfulness-guided exercise by a smartphone app has a positive impact on mental health and physical health.

Therefore, the primary purpose of this study was to analyze the effectiveness of mindfulness exercise guided by a smartphone app on negative emotions and stress in a non-clinical population to provide evidence of mindfulness exercise guided by a smartphone app on mental health.

This study involved a meta-analysis evaluation of the effects of mindfulness intervention guided by a smartphone app on negative emotions (depression and anxiety) and stress on a non-clinical population with emotional symptoms. Specifically, our study showed that mindfulness intervention guided by a smartphone app had a small-to-medium improvement effect on the negative emotions of the non-clinical population with emotional symptoms. The meta-analysis results were as follows: negative emotions (SMD = −0.272), depressive symptoms (SMD = −0.367), and anxiety symptoms (SMD = −0.490). The novel findings based on available evidence indicate that a favorable effect of mindfulness exercise guided by a smartphone app on reducing anxiety was found in the treated group compared to the untreated group. However, more studies with high homogeneity in methodology are needed to confirm these findings. The details of the study follow.

We included items of negative emotion data, four items of depression data (24, 26, 28, 29), and one item of stress data (25) from two studies (22, 23) to analyze the effect of mindfulness exercise guided by a smartphone app on negative emotions. The subjects included were mainly workers, students, nurses, and hospital staff. We speculate that the reason the researchers chose this kind of population is that the experimental subjects were relatively concentrated. Because of the particularity of each work or study, there was a higher chance of reducing negative emotions, especially medical workers. Our meta-analysis found that practitioners who practiced mindfulness exercises guided by a smartphone app exhibited a moderate effect of reduced negative emotions. This result was encouraging and indicates that mindfulness exercise guided by a smartphone app is effective in reducing negative emotions. Similarly, depression and anxiety calculations gave very similar results, both were also believed to be reduced through mindfulness exercise guided by a smartphone app. These benefits from the mindfulness exercise guided by a smartphone app to select text, audio, or video may be provided in these apps to explain mindfulness, which can help users practice mindfulness step by step and can provide long-term, detailed, and instructive mindfulness education for practitioners. Wen et al. found that the generation of negative emotions of medical workers was related not only to stress but also a factor of negative emotions in high-intensity medical work and that practicing mindfulness could help reduce the degree of fatigue of medical workers (23). Carissoli et al. pointed out that the mindfulness intervention time for the mindfulness exercise guided by a smartphone app should be more than 3 weeks to ensure that the practitioners have confidence (22). However, Bostock et al. found that 4 weeks of intervention exercises were not enough. To improve the benefits of mindfulness exercise, and thereby improve depression and anxiety, the development of mindfulness apps is necessary for the future (27).

In terms of reduced stress, we included a total of four studies. The meta-analysis results showed that the p was 0.054, which was higher than 0.05. Besides, the result had high heterogeneity, which led to this result. Potential sources of heterogeneity may include different tools to measure stress from four studies. After detailed analysis and interpretation of each study, Mistretta et al. found that there were significant differences in the stress variables of the mindfulness intervention group guided by the smartphone app, and studies have shown that such interventions are limited in reducing stress (24). A study by Hwang et al. found that mindfulness exercise guided by a smartphone app not only reduced nurses' feelings of pressure but also improved their self-efficacy (28). Therefore, we have reason to believe that mindfulness exercise guided by a smartphone app is a promising method for reducing personal stress.

Although mindfulness intervention with a smartphone app has certain advantages, the quality and intervention effect of many apps still needs to be explored. We speculate that there may be certain reasons why mindfulness exercise guided by a smartphone app has a small effect on students' depression and anxiety: (1) some apps may not thoroughly explain the concept of mindfulness, and some apps may not necessarily be related to mindfulness or meditation in terms of their functions or features. There is still no perfect standard for the concept of mindfulness and the steps of mindfulness training. (2) The functions of smartphone apps related to mindfulness training are limited, and most of them are aimed at short-term individual practices. There is no app for mindfulness professionals or those who want to carry out mindfulness training for a long time. Moreover, there is no possibility of group education or the practice of mindfulness. Therefore, although the smartphone app is a useful auxiliary medium for mindfulness intervention, its potential still needs to be explored to a large extent while improving its existing functions.

There were limitations to this study. First, the study data were retrieved in November 9, 2021, and the findings of possible related studies (ongoing studies, manuscripts under review, and studies published after that date) were excluded. Second, we only investigated the effect of mindfulness exercise guided by a smartphone app on the negative emotions and stress of a non-clinical population with emotional symptoms, but we did not investigate neural mechanism-related research. Third, only eight studies were included in this study; these relatively small number of studies translated to less overall real data, which may have affected the quality of research. Fourth, owing to the limited number of studies included, it was difficult to conduct subgroup analysis on intervention time and long-term effect after the intervention.

The results indicate that mindfulness exercise guided by a smartphone app shows potential advantages in reducing depression and anxiety in a non-clinical population with emotional symptoms. This suggests that mindfulness exercise guided by a smartphone app is of great significance in preventing emotional disorders and promoting mental health.

The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author/s.

JW, YM, and ZR contributed to the conception and design of the review. JW and YZ applied the search strategy. JW and KZ applied the selection criteria. ZZ and ZR completed an assessment of the risk of bias. YM analyzed and interpreted the data. JW and YM wrote this manuscript. YQ edited this manuscript. ZR is responsible for the overall project. All authors have read and approved the manuscript.

Research Foundation for Young Teacher of Shenzhen University (grant number QNJS0274); High-Level Scientific Research Foundation for the Introduction of Talent of Shenzhen University (grant number RC00228); High-Level Scientific Research Foundation for the Introduction of Talent of Shanwei Institute of Technology (grant number SKQD2021B-028); and the Natural Science Featured Innovation Projects in Ordinary Universities in Guangdong Province (grant number 2021KTSCX297).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer SL declared a shared affiliation with one of the authors, KZ, to the handling editor at the time of review.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.