Differences in incidence of suicide attempts between bipolar I and II disorders and major depressive disorder.

OBJECTIVES: Whether risk of suicide attempts (SAs) differs between patients with bipolar disorder (BD) and patients with major depressive disorder (MDD) is unclear. We investigated whether cumulative risk differences are due to dissimilarities in time spent in high-risk states, incidence per unit time in high-risk states, or both.
METHODS: Incidence rates for SAs during various illness phases, based on prospective life charts, were compared between patients from the Jorvi Bipolar Study (n = 176; 18 months) and the Vantaa Depression Study (n = 249; five years). Risk factors and their interactions with diagnosis were investigated with Cox proportional hazards models.
RESULTS: By 18 months, 19.9% of patients with BD versus 9.5% of patients with MDD had attempted suicide. However, patients with BD spent 4.6% of the time in mixed episodes, and more time in major depressive episodes (MDEs) (35% versus 21%, respectively) and in subthreshold depression (39% versus 31%, respectively) than those with MDD. Compared with full remission, the combined incidence rates of SAs were 5-, 25-, and 65-fold in subthreshold depression, MDEs, and BD mixed states, respectively. Between cohorts, incidence of attempts was not different during comparable symptom states. In Cox models, hazard was elevated during MDEs and subthreshold depression, and among patients with preceding SAs, female patients, those with poor social support, and those aged < 40 years, but was unrelated to BD diagnosis.
CONCLUSIONS: The observed higher cumulative incidence of SAs among patients with BD than among those with MDD is mostly due to patients with BD spending more time in high-risk illness phases, not to differences in incidence during these phases, or to bipolarity itself. BD mixed phases contribute to differences involving very high incidence, but short duration. Diminishing the time spent in high-risk phases is crucial for prevention.