In recent decades, as wireless network technology has become more pervasive and smartphone functionalities have advanced, there has been a noticeable trend towards younger individuals using smartphones. This trend has brought to light the issue of smartphone addiction among adolescents. Smartphone addiction is characterized by an inability to control phone use (1), leading to physiological issues like headaches and difficulty concentrating, as well as emotional challenges such as anxiety, depression, and reduced social adaptability (2, 3).Research has indicated that the global reporting rate of smartphone addiction was 28.3%, with variations observed across different cultural backgrounds, ranging from 10% to 31% (4). Eastern cultural backgrounds tend to report higher rates of smartphone addiction compared to Western cultures (5).

Another issue associated with smartphone addiction is the insufficient physical activity observed among adolescents globally (6). This lack of activity hinders the attainment of normal growth and development standards and has emerged as a significant public health concern. Research highlighted by Hallal showed that over 80% of adolescents worldwide failed to achieve the recommended 60 minutes of moderate-to-vigorous physical activity daily (7).

These aforementioned issues may be closely related to depression among adolescents. Depression, as one of the most prevalent mental disorders, affects approximately 350 million people of various ages worldwide. It is anticipated that by 2030, depression will constitute the largest global disease burden, posing a significant public health challenge to the international community (8). Adolescent depression is often considered to be a precursor of the adult depression and can lead to enduring social and psychological harm (9). Adolescents are particularly vulnerable to depression due to genetic, social, and environmental factors, resulting in a higher incidence compared to other age groups. Recent studies indicated a strong correlation between smartphone addiction, insufficient physical activity and psychological symptoms such as anxiety and depression. Tang et al. (2018) observed that adolescents and young adults addicted to mobile phones exhibited increased mental vulnerability, heightening their risk of depression (10). Additionally, individuals in Asian countries with smartphone addiction tended to have higher rates of depression compared to those in the United States. This suggested that cultural factors and environmental context should also not be ignored when exploring the impact of smartphone addiction and physical inactivity on adolescent mental health. Research among British adolescents aged 11-14 revealed a negative association between physical activity and depressive symptoms: increasing weekly exercise by 60 minutes reduced the risk of developing depressive symptoms by 8% (11). Furthermore, Kim et al. (2020) demonstrated that moderate-to-vigorous physical activity moderates the relationship between screen time and depressive symptoms (12). Studies on Chinese college students by Feng et al. (2014) and Wu et al. (2015) similarly found that those with both smartphone addiction and insufficient physical activity had a higher likelihood and severity of depressive symptoms (13, 14). However, there remains a paucity of research investigating the combined impact of smartphone addiction and insufficient physical activity on depressive symptoms, particularly in adolescents.

This study examined the prevalence of smartphone addiction, physical activity level, and depressive symptoms among secondary school students. It analyzed how smartphone addiction and insufficient physical activity impacted depressive symptoms. Additionally, it explored whether increased physical activity could mitigate the negative effects of smartphone addiction on depressive symptoms. The aim of this study is to provide insights for effective interventions targeting adolescent depression.

During adolescence, individuals undergo rapid psychological development, making them particularly susceptible to external influences that can result in various degrees of psychological issues. In this study, the prevalence of depressive symptoms among participants was 36.2%, significantly higher than both the 8% reported globally in previous studies on adolescent depression and the 26.3% prevalence observed among Chinese adolescents (22, 23). Despite potential influences from factors such as questionnaire tools, economic development, and social culture, this study consistently highlighted a high incidence of depressive symptoms among adolescents, underscoring the critical need for enhanced mental health interventions and improved adolescent mental health care. In addition, the study further revealed that adolescents who were non-only children or experience insufficient sleep duration demonstrated notably higher reporting rates of depressive symptoms, corroborating findings from prior research (24, 25).Future attention should prioritize the mental health needs of non-only children and adolescents with inadequate sleep duration, recognizing these factors as significant predictors of depression.

With the proliferation of smartphone technology, adolescents increasingly engage in activities such as communication, studying, and entertainment via smartphones. However, due to their ongoing development of self-control mechanisms, adolescents often struggle with smartphone addiction. This study found a 19.2% prevalence of smartphone addiction among participants. Smartphone addiction not only negatively impacts physical health, such as reduced vision and poorer sleep quality, but it can also contribute to various psychological issues including anxiety, depression, and reduced social adaptability (2, 26). This phenomenon poses significant public health challenges globally (27). Moreover, the study identified smartphone addiction as an independent risk factor for depressive symptoms, with significantly higher reporting rates among those addicted compared to non-addicted peers, aligning with previous research by Park et al. (2018) (28). The social replacement hypothesis posits that excessive smartphone use displaces real social interactions, potentially leading to negative emotions like depression (26, 29). Additionally, disruptions to circadian rhythms caused by smartphone use can impair neuroendocrine function, further predisposing adolescents to depressive symptoms (30). These findings highlight the urgent need for interventions targeting adolescent smartphone addiction. Strategies may include promoting face-to-face social interactions and offering educational resources to cultivate healthy smartphone use habits (31–33).

Notably, smartphone addiction often coexists with insufficient physical activity. The study reported prevalence rates of 37.7% for high physical activity, 39.1% for moderate physical activity, and 23.3% for insufficient physical activity among participants, reflecting a significant deviation from the UN’s recommended standards for adolescent physical activity. Prolonged physical inactivity not only contributes to physical ailments such as overweight and obesity but also serves as a key factor in the development of psychological disorders, including depressive symptoms (11). Thus, enhancing adolescent physical activity levels holds considerable importance for promoting both physical and mental well-being. Therefore, we recommend that physical activity promotion be included in public health strategies for adolescents. Schools and communities can work together to provide more accessible opportunities for sports and outdoor activities, which can both prevent physical health problems and improve mental health (34, 35).

This study also examined the combined effect of smartphone addiction and physical activity on the incidence of depressive symptoms. Compared to the students experiencing either smartphone addiction or insufficient physical activity alone, those affected by both conditions reported a higher prevalence of depressive symptoms. This finding was supported by previous research conducted by Liu et al. (2019) and Xie et al. (2019) (36, 37). When adolescents exhibited smartphone addiction, their likelihood of experiencing depressive symptoms was markedly elevated irrespective of their level of physical activity. This suggests that smartphone addiction exerts a more pronounced negative influence than insufficient physical activity, although higher levels of physical activity may partially mitigate the detrimental effects of smartphone addiction on adolescents’ depressive symptoms. The underlying rationale may stem from the possibility that smartphone addiction contributes to reduced physical activity levels, thereby nullifying the protective benefits of physical activity on mental health (38). In sight of this, interventions should not target smartphone addiction or physical inactivity in isolation, but also address both factors simultaneously, and policymakers and educators should develop comprehensive interventions to encourage reduced smartphone use and increased physical activity, providing practical solutions for incorporating healthy behaviors into adolescents’ daily lives. For example, schools and healthcare providers should implement targeted programs to educate adolescents about the importance of balancing smartphone use and physical activity, while encouraging daily physical activity, such as team sports or outdoor recreation, to help adolescents adopt a healthier daily lifestyle. In addition, parents should be educated about the signs of smartphone addiction and its impact on mental health, and provided with strategies regarding setting healthy boundaries in balancing smartphone use. By combining these strategies in both school and home environments, it is hoped that a more supportive environment can be created for adolescents to reduce their risk of developing or exacerbating depressive symptoms.

This study not only addresses a theoretical gap by providing a comprehensive analysis of smartphone addiction and physical activity, but also offers significant practical implications. The analysis of the combined effects of smartphone addiction and physical activity on depressive symptoms provides new insights for policymakers, urging the integration of support from all sectors of society to develop more effective, multifaceted intervention strategies aimed at addressing the increasing prevalence of adolescent depression. Furthermore, this study identifies additional key factors contributing to adolescent depression, including being a non-only child and sleep deprivation. These findings underscore the necessity for individualized interventions targeting these specific risk factors. Policymakers and mental health professionals can utilize these insights to design more targeted, evidence-based strategies to better mitigate the onset of adolescent depression. Additionally, the exploration of the interaction between various behavioral and demographic factors in the development of depression emphasizes the importance of a holistic approach to adolescent mental health. Several limitations of this study also need to be addressed. Firstly, the data were cross-sectional, precluding definitive conclusions regarding the causal relationships among smartphone addiction, physical activity, and depressive symptoms. Secondly, the study sample was confined to two secondary schools selected through cluster sampling, potentially limiting its generalizability to the broader adolescent population. Lastly, apart from height and weight, all variables were self-reported, which introduces the possibility of recall bias and reporting inaccuracies. Future studies should incorporate more objective assessment tools and adopt prospective methodologies to enhance data accuracy.

In summary, the prevalence of depressive symptoms among adolescents is substantial, with both smartphone addiction and insufficient physical activity posing significant challenges. A combined effect of smartphone addiction and insufficient physical activity on depressive symptoms was observed. Controlling smartphone addiction was found to be crucial in reducing the occurrence and progression of depressive symptoms in adolescents. Increasing levels of physical activity could partially mitigate the adverse effects of smartphone addiction on depressive symptoms. Therefore, comprehensive interventions targeting both smartphone addiction and physical activity are crucial for effectively managing the incidence and progression of depressive symptoms in adolescents.