To our knowledge, this is the first study using self-reported depressive and anxiety severity to separately investigate the relationship between current SR-SI and depressive and anxiety severity in patients with MDD and those with BPD. We found that depression severity had a positive association with increased risk for SR-SI in both patients with MDD and those with BPD although the magnitude of correlation was stronger in BPD than in MDD with R2=0.91 versus R2=0.64 (Figure 2B and 2C).
In contrast, anxiety severity had differential
associations with current SR-SI in MDD and BPD with no overall significant correlation between anxiety severity and current SR-SI in MDD (Figure 2B1), but significant linear correlation in BPD (Figure 2C1).
The finding of positive correlation between depressive symptom severity and current SR-SI is consistent with previous studies in different populations [7
]. A stronger correlation between depressive severity and current SR-SI in BPD than in MDD in the present study supports previous findings that differences in suicidality may exist between patients with MDD and those with BPD [3
]. The differences include a higher suicide rate in BPD than in MDD [3
] and more lethal suicide attempts in BPD than in MDD, especially in males [8
The positive correlation between anxiety symptom severity and current SR-SI in BPD is expected, but lack of correlation between anxiety symptom severity and current SR-SI in MDD is somewhat unexpected. These findings are not contradictory to most previous studies. As shown in Figure 2A, if analyzed the correlation between anxiety severity and current SR-SI as one group, the finding is consistent previous studies, i.e., levels of anxiety are associated with suicidal ideation [15
] and anxiety disorder increased risk for suicidal behavior [2
]. However, a previous clinical study in patients with BPD found that patients with or without anxiety disorders had no difference in the rate of previous suicide [45
]. Anxiety disorder was not associated with past suicide attempts or the severity of suicidal ideations. The inconsistency among these previous studies could be due to the studied population. More importantly, the majority of previous studies used lifetime anxiety disorder as a risk factor(s) [2
]. Only a few used anxiety severity [14
]. Some studies were cross-sectional [2
]; some were prospective [26
]; and others were retrospective [42
]. Clearly, it is difficult, if not impossible, to compare the results from these studies. Meanwhile, in present study SAS only includes symptoms of generalized anxiety and panic attacks, the symptoms of other anxiety disorders could not be measured.
Regardless, our results do suggest that anxiety symptom severity had differential associations with current SR-SI in patients with MDD and those with BPD, i.e., a “plateau” effect in MDD and a “linear” effect in BPD (Table 3 and Figure 2). Because there were only a small number of patients with severe anxiety symptoms in MDD, it remain unclear if higher anxiety symptoms would cause a decrease in current SR-SI compared to those with mild anxiety symptoms. Increase in anxiety severity with decreased risk for suicide attempt was speculated in an epidemiological study [46
The difference between MDD and BPD in suicidality was also reflected by the association between the number of comorbidities and current SR-SI, and between the number of comorbidities and past SA (Table 2). Those with ≥ 4 current comorbidities were associated with increased risk for current SR-SI and past SA in BPD (Table 2), suggesting that there might be a cumulative effect of comorbidities on suicidality in BPD as previously reported in epidemiological studies [2
]. In MDD, ≥ 3 comorbidities were associated with numerical increases in current SR-SI, but not with past SA (Table 2). Our previous studies have shown that patients with MDD had a fewer number of comorbidities than those with BPD [24
]. Fewer comorbidities in MDD and the “nonlinear” association of anxiety severity with current SR-SI in MDD are consistent with a lower rate of current SI in MDD than in BPD in the present study (Figure 1).
However, the similar rates of past SA in MDD and BPD (Figure 1) appeared to contradict these findings. Some epidemiological studies found that impulsivity and anxiety turned suicidal ideation to SA [2
]. In a study of the World Mental Health Surveys, parental generalized anxiety and depression were the only predictors of the onset and persistence of suicidal plans among offspring with ideation, whereas parental antisocial personality and panic disorder were the only predictors the onset of persistence of suicide attempts among ideators [46
]. Parental GAD had protective effect against planned suicide attempt among ideators, which was speculated that the high degree of worry might decrease the likelihood of carrying out the planned suicidal behavior. In the present study, patients with MDD and higher SAS scores having a lower rate of SR-SI than those with a lower SAS scores appeared to be consistent with this previous observation. It is possible that anxiety severity may also play different roles in other suicidal behaviors including SA in patients with MDD and those with BPD.
Our results suggest that the assessment of suicidality should be disease specific, especially when severe anxiety is a major concern. For patients with BPD, aggressive treatment of anxiety symptoms may reduce suicidal ideation, a precursor of most suicide attempt and suicide [2
]. For patients with MDD, attention should be paid to those even with mild anxiety symptoms. Since depressive symptoms had positive correlation with SI in both MDD and BPD, aggressive treatments of depression and anxiety may reduce the risk of suicidal ideation and other suicidal behavior [48