The finding was that stressful life events affect suicide risk in patients with MDD indirectly through distress tolerance. This finding provided a new psychopathology perspective on the prevention and intervention of suicide risk in patients with MDD.
Overall, the rate of suicide risk in patients with MDD was 75.2%, higher than in previous study[12]. This might due to sample selection bias that the majority of the MDD cohort were young patients. Young age was considered as one of the risk factors of suicide[33]. Compared to patients with MDD without suicide risk, patients with MDD with suicide risk had more severe depressive symptoms and more exposure to stressful life events. Patients with MDD exposed to stressful life events are more likely influenced by negative emotions which increased suicide risk. This finding was in line with previous study[12]. In addition, among patients with MDD, those with suicide risk had significantly lower levels of distress tolerance than those without suicide risk. Moreover, logistic regression analyses result showed that distress tolerance was a protective factor for suicide risk in patients with MDD. The finding of this study suggested that distress tolerance is an important indicator for the prevention and intervention of suicide in patients with MDD. Previous study also suggested that distress tolerance was considered as a feasibility indicator for suicide prevention[34].
As excepted, this study found that stressful life events were positively related with suicide risk. This finding was in line in with previous studies[12, 17]. The result showed that distress tolerance was negatively related with depressive symptoms. Lower levels of distress tolerance was associated with more severe psychological symptoms and outcomes[17]. Clinical studies have confirmed that improving distress tolerance can effectively reduce depressive symptoms, and distress tolerance has gradually become an important intervention indicator of psychotherapy[35]. Besides, it was found that distress tolerance was negatively related with stressful life events and suicide risk. Suicidal behavior has been conceptualized as a response to stress[36]. Not all individuals who have experienced stressful life events is at risk of suicide, which may be related to the individual's own ability to endure the negative emotions when exposed to stressful life events. Patients with MDD exposed to stressful life events experienced higher levels of negative emotion, which may reduce levels of distress tolerance. Individuals who can not withstand the negative emotion are more likely to be engaged in maladaptive coping strategies (such as suicide behavior) to avoid negative emotional states[34, 37]. Lower levels of distress tolerance was associated with increased risk of suicide. This was in line with the theory of suicide cube model proposed by Shneidman that one of reasons for committing to suicide is that individuals can not withstand distress status[38].
The mediation effect analyses results showed that stressful life events can positively predict suicide risk in patients with MDD. And distress tolerance can negatively predict suicide risk in patients with MDD. This finding of distress tolerance as a predictor of suicide risk was in line with a nonclinical sample study[25]. In addition, mediation analysis revealed a significant indirect effect of stressful life events on suicide risk, and the effect was completely mediated through distress tolerance. And the ratio of the mediating effect to the total effect was 60.0%. Hence, stressful life events affect suicide risk in patients with MDD indirectly through distress tolerance. Stressful life events are uncontrollable external environmental factor. Reducing the risk of suicide caused by life events by increasing the levels of distress tolerance in patients with MDD is a feasibility strategy.
This study provided a new perspective for the clinical intervention practice of suicide in patients with MDD. Clinicians should attach importance to the assessment of the levels of distress tolerance in patients with MDD, to facilitate the early identification of suicide risk and suicide prevention and intervention. Improving the levels of distress tolerance of patients with MDD can buffer the impact of stressful life events, then decrease the suicide risk. Base on the existing literature and the finding of the current study, further suicide prevention and intervention strategies should focus on increasing the levels of distress tolerance in patients with MDD.
There were several limitations to the present study. Firstly, this study was a cross-sectional study, where the stressful life events were collected retrospectively and recall bias might influence the results. Future studies should employ a longitudinal design to investigate the effect of distress tolerance on the relationship between stressful life events and suicide risk. Secondly, the study was conducted in a clinical sample of patients with MDD, which consequently limited the generalizability of the present findings to the healthy population. Future should examine to what extent the relationships generalize to the general population. Thirdly, the small sample size and single-center sampling limited the generalizability of the results. Finally, there were many factors that potentially affected risk of suicide in patients with MDD (e. g., the levels of social support and personality characteristics), and more other influencing factors will need to be considered in future studies.