Impulsive and Aggressive Behaviors
We found that impulsive and aggressive behaviors were associated with the risk of suicide in depression and that this effect was more important among younger cases (18 to 40 years). On the other hand, impulsive and aggressive behaviors were not direct predictors of suicide. It seems that these personality traits probably underlie the main predictors. This vision is supported by the positive correlation found between impulsive and aggressive behaviors and cluster B personality disorder and alcohol and drug abuse/dependence. It is possible to speculate that a developmental cascade may start with a biological predisposition to higher levels of impulsive and aggressive behaviors. Having a higher level of impulsive and aggressive behavior may, in turn, increase the risk of developing a cluster B personality disorder that, per se, could lead to an increased risk of substance abuse/dependence (66–68). This developmental hypothesis of suicidal behavior is also supported by at least one other study showing that borderline personality disorder alone was not a risk factor for suicide (30), but when it was comorbid with severe depression, the risk of dying by suicide was increased close to 450 times.
Age Effects
The effect of age on the mediating role of impulsive and aggressive behaviors and substance abuse/dependence on the risk of suicide was suggested by the stratified analyses. We have further explored this effect by investigating how these risk factors interacted with age in the regression model; however, the interactions were not retained in the final model. This is explained by the fact that although impulsive and aggressive behaviors and substance abuse/dependence are not significant risk factors in subjects older than 40, their effect is in a similar direction. In other words, these variables do not have opposite effects according to age.