This study has identified that mild to severe distress in interpersonal relationships was strongly associated with the 1-year risk of MDD among first-year college students. However, the independent predictive relationship between severe interpersonal distress and MDD incidence disappeared after controlling for baseline PHQ-9 scores. This indicates that the impact of interpersonal relationship on MDD incidence may be mediated by depressive symptoms. There was a multiplicative interaction between Dealing with People and PHQ-9 in relation to the risk of MDD, suggesting that the effect of distress in Dealing with People on MDD incidence was moderated by baseline depression. The distress in Dealing with People may increase the risk of MDD only among those with depressive symptoms.
The results of this analysis are consistent with previous studies. The etiology and pathogenesis of MDD are very complex and have not been fully elucidated. It may result from the joint action of many factors, such as the biological, psychological and social environment. Social behaviors and interpersonal relationship are indispensable parts of the social environment. It has been suggested that interpersonal style may account for some of the heterogeneity observed during MDD [25]. Depression has variations in interpersonal relationships. Thus, understanding and explaining the occurrence of depression needs to explore the role of interpersonal relationship factors in it [26]. There is a positive correlation between interpersonal conflict and depression severity [27]. Social dysfunction is sometimes the first sign of MDD and may lead to progressive social dysfunction [28]. For college students, one of the primary sources of stress is interpersonal conflict [29]. Physiological mechanisms suggest that increased inflammation in response to interpersonal life stress may increase the risk of depression in adolescents [30]. The findings of our study and of previous studies indicated that interpersonal relationships may be a predictor or a precursor of MDD among first-year medical students.
Among the first-year students with depression, interpersonal problems are more obvious. Poor interpersonal relationships are characteristic of a current MDD [17]. This also fits the theory that depressed people are more sensitive to interpersonal relationships [31]. Baseline depressive symptoms may play a mediating role in the effect of poor interpersonal relationship on MDD incidence. The mediating effect may be more significant in the group with more severe depressive symptoms. Thus, it may be partly explained that in the multivariate logistic regression analysis of this study, the influence of higher scores of 15–28 disappeared after adjusting PHQ-9, while lower scores of 9–14 still showed that interpersonal disturbance was a risk factor of MDD. There is a common interpersonal disturbance in patients with MDD [32], and the disturbance and depressive symptoms may influence each other [33].
On the four dimensions of interpersonal relationship, we have found that high scores were associated with high rates of the new-onset of MDD. However, the associations attenuated after controlling for the effect of baseline PHQ-9 score, except for Dealing with People. The scale adopted in this study focuses on the psychological barriers in communicating with the opposite sex. However, another cohort study has shown that a breakup with the opposite sex is a risk factor for major depressive episodes in adolescents [34]. Specific problems in relation to "dealing with people" are "Always try to make yourself appreciated", "Overly envious of others", "To be ostracized or fooled by others" and so on. These characteristics are similar to those of interpersonal dependence. Excessive interpersonal dependence has been linked to some mental illnesses, especially MDD [35]. It is also possible the significant interaction between Dealing with People and PHQ-9 scores was found by chance. Future studies are needed to confirm that the distress of Dealing with People and the risk of MDD only exist in people with depressive symptoms.
This study has some implications for the prevention and treatment of MDD. On the one hand, adjusting interpersonal relationships is crucial for preventing the onset of MDD in first-year students. Studies have shown that increasing the duration of a positive relationship is beneficial for the mental health [36]. To be specific, for intimate relationships, parents should be more supportive of their children and reduce negative parent-child interactions [37]. Conversation is how young people prefer; we can ease depression by talking with others [38]. Additionally, interpersonal psychotherapy (IPT) may be adopted to prevent minor and moderate depression, which is supported by solid evidence [39, 40]. In the future, it would be beneficial to develop different approaches to improve and maintain the interpersonal relationship among people with depression.
The strengths of this study include a prospective cohort study design which can better examine the relationship between interpersonal relationships and new-onset of MDD in first-year college students. Few studies had focused on the interpersonal relationship and the risk of MDD in this population. Although many theories report that interpersonal relationships might contribute to the development of depressive symptoms, there have been few large cohort studies to provide robust evidence. This study also adjusted for multiple confounding factors to minimize the confounding effects. In addition, the study population is first-year students. Freshmen are at a unique stage of their transition from family and school relationships to larger social relationships. Thus, this analysis provided evidence about the association between interpersonal relationship and MDD from the developmental and life course perspective.
There were several limitations in this study. First, self-report tools may have certain subjective effects and recall bias. Secondly, the etiology of MDD is complex, and many factors were not able to be included in the analysis. Thirdly, the time interval from baseline to follow-up in this study was one year, and the impact of interpersonal relationships on the new onset of major depression could be longer term. Future studies with longer follow-up period would be helpful. Finally, this study was conducted only in Shandong, China, which may be influenced by geographical and socio-economic factors. In addition, college freshmen are concentrated in medical schools, which may limit the generalization of the findings. Longitudinal studies on this topic in different regions and different university settings are needed.