Does Insomnia Increase the Risk of Suicide in Hospitalized Patients with Major Depressive Disorder? A Nationwide Inpatient Analysis from 2006 to 2015

Introduction. Insomnia is an important symptom associated with major depressive disorder (MDD). In addition, it is one of the risk factors for suicide. Studies have shown the relationship be-tween insomnia and suicidal behavior in patients with MDD. However, this association has not been evaluated in a large sample of hospitalized patients. Objectives. To evaluate the suicidal be-havior in MDD patients with insomnia compared to those without insomnia. Methods. From the National Inpatient Sample (NIS 2006-2015) database using the ICD-9 code, patients' data were obtained with the primary diagnosis of MDD and comorbid diagnosis of insomnia disorders (MDD+I). These patients were compared with MDD patients without insomnia disorders (MDD-I) by performing a 1:2 match for the primary diagnosis code. Suicidal ideation/attempt da-ta were compared between the groups by multivariate logistic regression analysis. Results. After the diagnostic code matching, 139061 patients were included in the MDD+I group and 276496 patients in the MDD-I group. MDD+I patients were older (47 years vs. 45 years, p < 0.001) com-pared to the MDD-I group. The rate of suicidal ideation/attempt was 56.0% in the MDD+I group and 42.0% in the MDD-I group (p < 0.001). After adjusting for age, sex, race, borderline personal-ity disorders, anxiety disorders, and substance use disorders, 'insomnia' was associated with 1.71 times higher odds of suicidal behavior among MDD patients admitted to the hospital. (Odds ratio: 1.71, 95% confidence interval 1.60-1.82, p < 0.001). Conclusions. Insomnia among MDD patients is significantly associated with the risk of suicide. MDD patients with insomnia need to be closely monitored for suicidal behavior.