College students are undergoing a significant transition as they progress from adolescence to adulthood [1], making them more vulnerable to behavioral and psychological health problems due to their immaturity and lower self-regulatory skills [2]. Depressive symptom is one of the most prevalent psychiatric illnesses in this population. The pooled prevalence of generalized depressive symptoms among college students was reported to be 33.6% [3]. Concurrently, smartphone addiction is currently recognized as a public health problem, especially among college students [4]. It is defined by the excessive use of smartphones and an inability to regulate that use [5]. As a subtype of internet addiction [6], it exhibits neurobiological features akin to other addictive behaviors [7], including preoccupation, loss of control, tolerance, withdrawal, and relapse [8]. Epidemiological studies have highlighted a high prevalence of smartphone addiction among college students, ranging from 12.8% in Spain [4] to 59% in Egypt [9], with a reported prevalence of 52.8% in China [10].

Given the high prevalence of depressive symptoms and smartphone addiction among college students, researchers have increasingly focused on the potential interplay between the two conditions [11,12]. Several studies have documented a positive relationship between depressive symptoms and smartphone addiction [11]. Individuals with depressive symptoms use their smartphones repeatedly to alleviate their mood symptoms, which in turn leads to smartphone addiction [13]. Conversely, depressive symptoms may be a side-effect of smartphone addiction, which can cause neuroplastic changes in the brain and result in mood disorders [14]. Moreover, a bidirectional relationship has also been found that two conditions mutually reinforce each other’s adverse consequences [12]. This bidirectionality is consistent with the broader literature on psychiatric comorbidity, which shows that addictive disorders often co-occur with depressive symptoms [15]. For instance, 25% of individuals with substance use disorder have a comorbid depressive disorder [16]. Based on the bidirectional models of comorbidity, the ongoing and interactive effects of psychiatric disorders account for increased rates of comorbidity [17]. Therefore, we thought that the comorbidity between smartphone addiction and depressive symptoms might exist. However, this comorbidity has not yet been well studied.

While direct research on the comorbidity between smartphone addiction and depressive symptoms is limited, insights can be drawn from studies on internet addiction. Previous studies have observed comorbidity between internet addiction and depressive symptoms, with prevalence rates ranging from 0% to 75% [18]. According to common factor models, such high rates of comorbidity result from shared vulnerabilities to both disorders [17], such as dysfunctions in dopaminergic pathways [19] and transcription factors like brain-derived neurotrophic factor (BDNF) [15]. In addition, males [20], weekly hours of internet use [21], and negative peer relationships [22] have been identified as predictors of the increased risk of comorbidity between internet addiction and depressive symptoms. Given the conceptual and behavioral overlap features between internet and smartphone use [23], we thought that smartphone addiction and depressive symptoms might share similar biological mechanisms and risk profiles.

Notably, individuals with comorbidity showed more severe psychopathological impairments [24]. It is often associated with poor prognosis, leading to more severe clinical features and a greater medical burden than either condition alone [25]. Understanding the occurrence of this comorbidity and recognizing its associated profiles are critical for the proper prevention and treatment of behavioral addiction and psychological problems [15]. Therefore, it is necessary to analyze the prevalence of comorbidity between smartphone addiction and depressive symptoms, as well as the related factors. However, research comparing the correlates of smartphone addiction only, depressive symptoms only, and comorbidity among college students is lacking.

To address these gaps, this study aimed to assess the prevalence of comorbid smartphone addiction and depressive symptoms and to identify the shared and distinct factors of single and comorbid problems among college students. The outcomes of this study will provide a foundation for future research on comorbidity and enhance our understanding of the relationship between smartphone addiction and depressive symptoms. Moreover, the findings will offer valuable insights for developing preventive strategies, thereby facilitating early identification and intervention to improve the mental health outcomes of college students.

This study examined the prevalence of smartphone addiction alone, depressive symptoms alone, and their comorbidity among college students, as well as associated factors. The results indicated that the prevalence of smartphone addiction was 30.5%, while the comorbidity was 25.3%, exceeding the 8.9% with depressive symptoms alone among college students. Four, five, and ten risk factors were associated with smartphone addiction only, depressive symptoms only, and their comorbidity, respectively. Higher frequency of mobile phone use in lessons and lower level of school belonging were the common predictors of all three disease outcomes. Generally, exposure to more risk factors increased the likelihood of these outcomes, with a 92% probability of comorbidity among medical students exposed to all ten risk factors.

Compared with other studies, our study found that college students had a slightly higher prevalence of smartphone addiction alone (30.5%) but a lower rate of depressive symptoms alone (8.9%). A systematic review showed that the prevalence of smartphone addiction in young people was 23.3% [29]. This highlights potential public health concerns linked to smartphone use among college students [30]. Furthermore, the prevalence of depressive symptoms only in our study sample was lower than that in previous studies, such as in Nigeria (9%) [31], Iran (37%) [32], and Africa (40.1%) [3]. The discrepancies in the figures can be attributed to the use of different measurement methods and sample sizes. Notably, compared to the study on the comorbidity of internet addiction and mood symptoms (13.6%) [33], college students have slightly higher rate of the comorbidity of smartphone addiction and depressive symptoms (25.3%). One study found that the prevalence of the comorbid depressive symptoms among individuals with addictive behaviors was 2.59 times higher than among individuals without addictive behaviors [25]. The high comorbidity rate indicates a growing mental health crisis among college students. Depressive symptoms with comorbid addictive behavior may lead to greater academic impairment, reduced quality of life, and huge psychiatric burden [25]. Addressing smartphone addiction and depressive symptoms in isolation may overlook their interaction. Therefore, it is crucial to recognize and address this comorbidity in order to prevent severe clinical outcomes in college students.

Our findings revealed that smartphone addiction and depressive symptoms share overlapping pathogenic factors. After correction for multiple tests, males had a higher risk of comorbid smartphone addiction and depressive symptoms, which is consistent with previous studies on internet addiction and depressive symptoms [34,35]. Compared to females, males tend to spend more time on online gaming by using smartphones, adopt social interaction avoidance strategies [36], and are more prone to addiction. However, some studies have reported the opposite conclusion [37,38]. Meanwhile, other studies have found no sex difference in the comorbidity of addictive behaviors and depressive symptoms [30,39]. Thus, these inconsistent findings need to be further explored to determine how sex affects this comorbidity.

Notably, our study demonstrated that students from families with more than one child were a significant predictor of suffering from both smartphone addiction only and comorbidity. This support prior research indicating that students with siblings are more susceptible to addictive behaviors [40] and depressive symptoms [2]. Moreover, lower-middle-level family income is a high risk of depressive symptoms only and comorbidity. Previous findings have indicated that high-income levels are significantly associated with a lower risk of depressive symptoms [41,42]. Besides, individuals from families with lower-middle-level income are more susceptible to smartphone addiction [43]. One possible reason for this is that students from low-income families see smartphones as a way to escape from the psychological burden of their daily life [43]. However, this finding is inconsistent with other studies that students from higher income families spend more time on their smartphones [44].

This study identified a link between excessive internet daily use (>7 hour) and smartphone addiction, consistent with previous research [45]. Poor self-control and self-regulation in smartphone use can foster problematic habits [46]. Excessive internet daily use was also a contributing factor to the comorbid smartphone addiction and depressive symptoms, potentially explained by the compensatory internet use theory [13]. Individuals may use smartphones excessively to cope with negative emotional situations and to fulfill psychological needs that may not be met in the real world [13]. In addition, the frequency of mobile phone use in lessons was correlated with all three outcomes. College students with smartphone addiction tend to use their phones frequently in class [47]. As highlighted in an integrative review, excessive smartphone use in lessons distracts students from their focus, impairs their academic performance, and may increase their vulnerability to depression [48].

Consistent with previous studies, poor parent-child relationships were related to elevated depressive symptoms among college students [49,50] and to the co-occurrence of depressive symptoms and smartphone addiction. Emotional warmth is a fundamental aspect of a good parent-child relationship [51]. Those with strained parent-child relationships often exhibit poorer emotion regulation skills and perceive less emotional support, making them more vulnerable to depressive symptoms [49]. Furthermore, negative parenting styles were associated with depressive symptoms only. Individuals who experienced less parental warmth and more parental rejection were at an increased risk of depression [52]. In line with the study on the comorbidity on internet addiction and depressive symptoms [53], negative parenting styles were also the risk factors for the overlap of smartphone addiction and depressive symptoms. Satisfying basic psychological needs is crucial for adolescent development [54]; however, negative parenting styles, such as parental rejection, can undermine these needs [55]. Lacking family support and facing emotional rejection, students are more prone to psychological issues and may turn to excessive smartphone use to compensate for these unmet needs, which can lead to addictive behavior.

In addition, we also found that poor roommate relationships were associated with depressive symptoms. Both poor classmate relationship and poor roommate relationship were linked with the risk of comorbid smartphone addiction and depressive symptoms. College students are heavily influenced by their peers in school [56]. Students with poor peer relationships may experience less social support and greater isolation, leading to diminished social connectedness [57]. Lower social connectedness has been found to be correlated with mental health problems [58] and higher health-risk behaviors. Notably, school belonging was a significant predictor of all three outcomes. In line with prior research, college students with a strong school belonging were less likely to develop smartphone addiction [59]. A sense of belonging influences individuals’ cognition, emotions, and behaviors [60]. When the sense of belonging cannot satisfy students’ needs in school, a series of negative outcomes could occur, such as depressive symptoms and addictive behaviors.