The Kyungpook National University School of Medicine conducted mental health assessments on students annually from 2009, and the data used in this study were drawn from three grades (premedical first grade, medical first grade, medical third grade) from 2017 to 2020. The students responded to self-report questionnaires through a computer-based test. In the case of the results of the subjects who performed the tests more than once as follow-up observations, only the first test results were analyzed.

In proportion to the sex distribution of all medical students, the data of 866 students, consisting of 613 men (70.8%) and 253 women (29.2%), were included in the final analysis. According to the distribution by grade, 356 (41.1%) were first-year premedical students, 297 (34.3%) were first-year medical students, and 213 (24.6%) were third-year medical students.

This study was approved by the Institutional Review Board of Kyungpook National University School of Medicine (IRB No. 2021-0086). All of the subjects were fully informed about the aims and methods of the study, participated voluntarily, and gave written informed consent prior to their participation in this study.

The Perceived Stress Scale (PSS) is an instrument used to measure the level of stress experienced over the past month. In this study, we used the Korean version of the PSS, which has a Cronbach’s α value of 0.82 [30]. A total of 10 questions are evaluated along a scale of 0 (never) to 4 (very often) points. Questions 4, 5, 7, and 8 are negative questions and are back-scored. The total range is 0 to 40 points. The higher the total score, the greater the perceived level of stress.

The Connor-Davidson Resilience Scale (CD-RISC) is used to evaluate resilience related to coping skills in stressful events. The Korean version of the CD-RISC features excellent internal consistency and was developed in 2010 (Cronbach’s α>0.9) [31]. It consists of a total of 25 questions, and each item is evaluated with a score of 0 (not at all) to 4 (extremely) points. The scores of all items are summed, with a higher score indicating greater psychological resilience.

The Rosenberg Self-Esteem Scale is a measurement that evaluates an individual’s self-esteem, which is the level to which one respects oneself and the level to which one considers oneself worthwhile. A total of 10 questions are evaluated with a score of 0 (not at all) to 3 (extremely) points, and Questions 3, 5, 8, 9, and 10 are scored inversely. Higher scores indicate higher self-esteem. In this study, the scale tool which was developed by Rosenberg and cited by Yoo et al. [32] was used (Cronbach’s α=0.86).

For each addictive behavior (internet, smartphone, and alcohol use), we used Pearson’s chi-square test to compare the sex and grade-level differences in the prevalence of high-risk and potential-risk groups. A one-way analysis of variance was used to compare the differences in the levels of the addictive behaviors and psychological variables (stress, resilience, and self-esteem) among the three groups (premedical first grade, medical first grade, medical third grade). The same differences were also tested between male and female students by means of a t-test.

To analyze the relationship between addictive behaviors and psychological variables, zero-order and partial correlation analyses with sex and grade corrections were performed. For the purpose of correcting for multiple testing, the Bonferroni correction was applied to statistical significance calculations.

Since stress, resilience, and self-esteem are overlapping and correlated concepts, various mediation models need to be considered. However, this study focused on the roles of resilience and self-esteem as mediators in the relationship between stress and addictive behaviors, based on a previously confirmed mediation model [25]. The effects of self-esteem and resilience as mediators of the association between stress and addictive behaviors were analyzed via a parallel mediation model after controlling for sex and grade. This analysis was completed with the Statistical Package for Social Sciences (SPSS) PROCESS macro, version 3.5 (model 4). The bootstrapping method was used in this analysis. The calculated confidence intervals (CIs) were used to determine whether each effect (i.e., direct, indirect) was statistically significant. For each effect, we examined the 95% CI and if the value of 0 did not fall within the range of the CI for that effect, then the effect was deemed to be statistically significant.

We performed all statistical analyses using SPSS, version 20.0 (IBM Corp., Armonk, NY, USA). For these analyses, a two-sided test at the 0.05 level was used to evaluate statistical significance.

Table 1 represents the prevalence of addiction in internet, smartphone, and alcohol use. Among the entire sample of students, the prevalence of potential-risk and high-risk users was 5.8%, and 1.7% for internet use, and 5.4% and 2.2% for smartphone use, respectively. Moreover, for alcohol use, the prevalence was higher than that of the other addictive behaviors, with the prevalence of at-risk drinking group being 22.6% and the prevalence of the high risk-drinking group being 5.3%.

In terms of grade, the risky internet users, who met the high-risk or potential-risk categories, increased from 4.8% to 8.4% to 10.8% as they were going up in grade (χ²=7.5, p=0.023). The risky alcohol users also tended to increase from 23.9% to 28.3% to 34.3% (χ²=7.18, p=0.028). In contrast, the number of risky smartphone users showed no statistical difference according to grade. Additionally, there was no sex difference in the prevalence of risky users of the internet and smartphone, while the prevalence of risky alcohol users was higher in females than in males (χ²=13.79, p<0.001).

Table 2 shows the quantitative differences by grade and sex for each addiction behavior. For grade-level differences, the first-year premedical students showed significantly lower scores on internet and smartphone use than both the first and third-year medical students did. However, there was no grade-level difference in alcohol use. Regarding the difference between the sexes, males reported higher scores than females in the internet and alcohol use but not in the smartphone use.

Among psychological variables, perceived stress in the first-year premedical students was significantly lower than that in observed the other two grades, whereas resilience and self-esteem in the first-year premedical students were higher than those observed in the first-year medical students. Meanwhile, self-esteem was the only variable that showed a significant sex difference, with scores being higher in males than in females.

Table 3 shows the correlations between the psychological variables and the addictive behaviors. Stress was positively correlated with internet use and smartphone use (all Ps<0.001). Resilience was negatively correlated with internet use and smartphone use (all Ps<0.001). Self-esteem was also negatively correlated with internet use and smartphone use (all Ps<0.001). These relationships remained significant after controlling for sex and grade. However, the level of alcohol use was not correlated with stress, resilience, or self-esteem, regardless of whether sex and grade were controlled.

The regression model for each addictive behavior was found to be statistically significant (all Ps<0.001). In addition, for the analysis of statistical power, the R² values associated with the F-tests of the addictive behavior models were: in the internet use model, 0.27 (self-esteem as the outcome), 0.16 (resilience as the outcome), and 0.25 (internet use as the outcome); in the smartphone use model, 0.27 (self-esteem as the outcome), 0.16 (resilience as the outcome) and 0.24 (smartphone use as the outcome); and in the alcohol use model, 0.27 (self-esteem as the outcome), 0.16 (resilience as the outcome), and 0.05 (alcohol use as the outcome). According to the standard for R² values proposed by Cohen [33], the statistical power of our study is above the medium level (R²=0.13), with the exception of the alcohol use model.

The mediating effects of resilience and self-esteem on stress and each addiction behavior were different (Table 4). For internet use, resilience and self-esteem mediate the relationship between stress and internet use. In addition, the sum of the indirect effects was 0.20, which was statistically significant, as the 95% CI (0.15-0.24) did not include 0. For smartphone use, a statistically significant indirect effect of stress on smartphone use was revealed through resilience but not through self-esteem. Moreover, the sum of the indirect effects was 0.18, which was statistically significant, as the 95% CI (0.13-0.24) did not include 0. On the other hand, for alcohol use, the 95% CIs for the indirect effect contained 0, suggesting that neither resilience nor self-esteem was a significant mediator on the effect of stress on alcohol use. Figure 1 depicts the summary of the relationship between stress, resilience, self-esteem, and each addiction behavior.

In the literature, the prevalence of addictive behaviors of medical students varies greatly from study to study [5,10-14]. For risky users, the prevalence was 5.6%-52.4% for internet, 4.4%-60.3% for smartphones, and 15.4%-45.5% for alcohol [5,10-14]. These discrepancies between studies may be due to differences in the measurement scale (including cut-off values), the educational environments, the sample size and distribution, and the socio-cultural backgrounds. However, the prevalence of risky internet use and alcohol use in our study seems to be similar to that of the Korean general adult population in other surveys using the same measurement scale (internet use: 5.8%, and alcohol use: 33.2%) [15,16]. Thus, the prevalence in this study is indicative of potential public health concerns regarding addictive behaviors among medical students.

In this study, qualitative and quantitative analyses demonstrated characteristic changes of use pattern among three grades. The mean scores of internet and smartphone use were higher in the first and third graders of the medical school than in the first graders of the premedical school. These findings indicated that the general use of the internet and smartphone was increased during this period. In contrast, an increase in the proportion of risky users was not observed in smartphone use, though it was in internet use, as grade increased.

The first graders of the premedical school who took the painful entrance exam enjoyed the joy of experienced entering medical school, so their level of stress were low, and their internet and smartphone use was believed to be less than that of other grades [20]. In fact, consistent with previous study [34], perceived stress was found to be higher in the first and third graders of the medical school than in the first graders of the premedical school in this study. These observations support the notion that the internet and smartphone are used as means by which to reduce stress from negative emotions [35]. Another explanation of the general increase of internet and smartphone use may be due to heightened accessibility, as university students can access the internet and smartphone more freely than high school students can. Third, social influences should also be considered. Internet use and smartphone use (being connected online) have become social norms, and there are expectations of constant reachability [36]. According to Erikson’s developmental stages, the developmental task of early adulthood is to expand the sense of intimacy by forming meaningful interpersonal associations with others while increasing interest in others [37]. In this process of psychosocial development, it is a process in which the use of the internet or smartphone itself reacts to social conformity as a result of peer pressure [38]. In addition, based on the social learning theory, the use of the internet and smartphone can also be viewed as a process of adapting to social life by modeling social surroundings [39]. Therefore, in the process of adapting to university life, it can be considered that the use of the internet and smartphone would gradually increase. Although both internet and smartphone use increased, the prevalence of risky users only increased with respect to internet use. We assume that risky internet users may include internet users for entertainment purpose, such as multi-user online games or gambling games, which may be more addictive than smartphone [40]. Future studies are needed to see what kinds of contents lead risky internet users.

On the other hand, although no significant differences in the mean scores of alcohol use were found, risky alcohol users increased from 23.9% to 28.3% to 34.3% as grade level increased, and this prevalence was higher than that of other addictive behaviors in this study. Unlike internet and smartphone use, alcohol did not show generally increased use according to grade partially because exposure to alcohol is less frequent than internet and smartphone use. Nevertheless, the reason why the proportion of risky alcohol users increases is that alcohol addiction may be more biologically susceptible than the other addiction behaviors. Last but not least, it should be noted that there were no statistical differences between the first and third medical students in the mean scores of all addictive uses and psychological variables in this study.

Consistent with previous studies [40], males generally reported to use the internet more than females in this study. However, there was no difference in the prevalence of risky users. These results could be explained by differences in the internet usage preferences of males and females. Whereas females prefer social network services, males prefer to use the internet for entertainment purposes, such as multi-user online games, which may be more addictive [40]. For smartphone use, there were no sex differences in general use or in the prevalence of risky users. Regarding alcohol use, the mean score of females was lower while the prevalence in the risk drinking group is higher in females than in males. Interpretation of these results should be cautious because the cutoff value of risky drinking is lower in for females than for males. However, this difference may not come solely from different cutoff values. In fact, the sex gap in the prevalence of alcohol use disorder has been rapidly decreasing over time in South Korea. In particular, the prevalence of alcohol use disorder among young women is increasing [41], which may be indicative of a phenomenon caused by an increase in women’s social advancement and socio-cultural changes, such as the shift to a more permissive drinking culture.

There were significant correlations between stress and internet use and smartphone use, and these associations were well shown in regression analysis. Stress is thought to play a role in the development of addiction by increasing craving and motivation toward the addictive behavior [42]. The association between stress and addictive behaviors may be bidirectional; such addictive behaviors may be used as a means of reducing stress, and blunted stress responses may confer an increased risk of engaging in addictive behaviors [42].

On the other hand, in the regression analysis, there were no association was observed between alcohol and stress as in the previous study [7], and this was the same in correlation analysis. Based on studies showing that alcohol is used as a kind of countermeasure to unpleasant things or situations and that alcohol has the effect of self-treatment in buffering stress in life [43], it was thought that stress affected alcohol use. However, from a neurobiological point of view, alcohol (substance addiction) directly affects the dopamine system of the brain, whereas behavioral addictions only indirectly affect these systems [44]. Also, alcohol, unlike behavioral addiction, is accompanied by a physiologically distinct and medically serious withdrawal condition [44]. In these respects, alcohol could be considered to have a greater effect on addiction. Moreover, alcohol use seems to be more genetically innate than behavioral addictions (e.g., internet use) [45]. Therefore, it could be considered that alcohol causes addiction through a much more complex and diverse pathway that stress alone cannot explain.

Aside from directly affecting addictive behaviors, stress also had indirect effects through resilience and self-esteem in this study. That is, resilience acted as mediating role with respect to the effect of stress on internet use and smartphone use, and self-esteem acted as mediating role with respect to the effect of stress on internet use. The medical students who perceived high stress had lower resilience or self-esteem, resulting in higher levels of addictive behaviors, while those who perceived low stress had higher resilience or self-esteem, contributing to lower levels of addictive behaviors. Resilience and self-esteem were associated with positive emotions, which protect mental health by controlling the negative effects of stress [46,47]. Moreover, it was found that people with high resilience and people with high self-esteem possess many psychological resources, including tranquility, optimism, and openness [46,48], and are more likely to find positive meaning in problems that they have to face [46,48]. Based on the protective factor model [49], these positive personal attributes reduce the negative influence of stress on adaptive behaviors. Thus, people with high resilience and people with high self-esteem are less likely to engage in addictive behaviors.

According to the results of this study, it would be helpful to provide premedical students with education focused on the primary prevention of addiction. For junior medical students who go through drastic changes in their learning systems, the management of their academic performance and its associated stress is critical. For senior medical students, school authorities need to focus more on the detection and treatment of students at risk because we observed that there were no general increases in addictive behaviors between first and third grade medical students. Moreover, intervention strategies to enhance resilience and self-esteem should be considered, especially with respect to internet and smartphone use, as the improvement of resilience and self-esteem is crucial in alleviating maladaptive coping and in further promoting coping mechanisms [48], resulting in lower levels of addictive behaviors.

This study has several limitations. First, since our study was a cross-sectional study, we were unable to determine definite causal relations among stress, resilience or self-esteem, and addictive behaviors. Second, the data were obtained through self-reported questionnaires, which could lead to response bias. Third, the ratio of male and female students in this study was approximately 7:3. Although it was proportional to the proportion of the total student distribution, there were a possibility of selection bias. Thus, we have tried to control sex as a covariate in the correlation analysis and mediation analysis. Fourth, due to a lack of data on other variables, including living status, academic performance, and psychological symptoms, the relationships between these factors and addictive behaviors were not considered. Fifth, since this study focused on students from a single medical school, we should be careful in generalizing our results. Further prospective studies of medical students of all grades, including those attending other universities, are needed to compensate for our limitations. Nevertheless, our study has the following strengths. For the first time, we investigated the prevalence of various addictive behaviors by grade and their associations with stress through resilience and self-esteem on various addictive behaviors in Korean medical students.

In conclusion, our study suggests that addictions in medical students are as prevalent as among the general population and that the prevalence may increase with increasing grade in medical school. We also suggest that internet use and smartphone use may be better explained by stress than alcohol use, with resilience and self-esteem acting as mediators in their relationships. This study may provide valuable information for the relevant university and medical school authorities responsible for managing addictive behaviors in medical students.