Bipolar depression and suicidal ideation: Moderators and mediators of a complex relationship

Introduction: Not all patients with bipolar depression have suicidal ideation (SI). This study examines some factors that link bipolar depression to SI. Methods: 482 individuals with bipolar I or II were randomized to either lithium or quetiapine plus adjunctive personalized therapy in a 24 week comparative effectiveness trial. Severity of depression and SI were assessed with the Bipolar Inventory of Symptoms Scale (BISS). We examined potential moderators (age, gender, age of illness onset, bipolar type, comorbid anxiety, substance use, past suicide attempts, childhood abuse and treatment arm) and mediators (severity of anxiety, mania, irritability, impairment in functioning (LIFE-RIFT) and satisfaction and enjoyment of life (Q-LES-Q)) of the effect of depression on SI. Statistical analyses were conducted using generalized estimating equations with repeated measures. Results: Bipolar type and past suicide attempts moderated the effect of depression on SI. Life satisfaction mediated the effect of depression and SI. The relationship between anxiety, depression and SI was complex due to the high level of correlation. Treatment with lithium or quetiapine did not moderate the effect of depression on SI. Limitations: Suicide assessment was only done using an item on BISS. Patient population was not specifically chosen for high suicide risk. Discussion: Individuals with Bipolar II experienced more SI with lower levels of depression severity. A history of suicide predisposed patients to higher levels of SI given the same severity of depression. Reduced life satisfaction mediates the effect of depression on SI and may be a target for therapeutic interventions.