Sleep duration, but not insomnia, predicts the 2-year course of depressive and anxiety disorders

OBJECTIVE: To examine the predictive role of insomnia and sleep duration on the 2-year course of depressive and anxiety disorders.

METHOD: This study is a secondary data analysis based on data from the baseline (2004-2007) and 2-year assessment of the Netherlands Study of Depression and Anxiety. Participants were 1,069 individuals with DSM-IV-based depressive and/or anxiety disorders at baseline. Sleep measures included insomnia (Women’s Health Initiative Insomnia Rating Scale score ≥ 9) and sleep duration (categorized as short [≤ 6 hours], normal [7-9 hours], or long [≥ 10 hours]). Outcome measures were persistence of DSM-IV depressive and anxiety disorders (current diagnosis at 2-year follow-up), time to remission, and clinical course trajectory of symptoms (early sustained remission, late remission/recurrence, and chronic course). Logistic regression analyses were adjusted for sociodemographic characteristics and chronic medical disorders, psychotropic medications, and severity of depressive and anxiety symptoms.

RESULTS: The effect of insomnia on persistence of depressive and/or anxiety disorders (OR = 1.50; 95% CI, 1.16-1.94) was explained by severity of baseline depressive/anxiety symptoms (adjusted OR with severity = 1.04; 95% CI, 0.79-1.37). Long sleep duration was independently associated with persistence of depression/anxiety even after adjusting for severity of psychiatric symptoms (OR = 2.52; 95% CI, 1.27-4.99). For short sleep duration, the independent association with persistence of combined depression/anxiety showed a trend toward significance (OR = 1.32; 95% CI, 0.98-1.78), and a significant association for the persistence of depressive disorders (OR = 1.49; 95% CI, 1.11-2.00). Both short and long sleep duration were independently associated with a chronic course trajectory (short sleep: OR = 1.50; 95% CI, 1.04-2.16; long sleep: OR = 2.91, 95% CI, 1.22-6.93).

DISCUSSION: Both short and long sleep duration-but not insomnia-are important predictors of a chronic course, independent of symptom severity. It is to be determined whether treating these sleep conditions results in more favorable outcomes of depression and anxiety.