Relationship between insomnia and depression in a community sample depends on habitual sleep duration.

Sleep disturbances, such as short sleep duration and insomnia, are core features of depression. However, it is unclear if sleep duration and insomnia have an interactive effect on depression severity or individual symptoms. Data were drawn from a community sample (N = 1007) containing responses on the Insomnia Severity Index, Patient Health Questionnaire-9 (PHQ-9), and average sleep duration. Regression analyses determined the prevalence risks (PR) of symptoms of depression based on insomnia severity and sleep duration. Depression severity was related to insomnia severity (PR 1.09, p < 0.001) and short sleep duration (PR 1.52, p < 0.001), but the interaction between the two was negative (PR 0.97, p < 0.001). Insomnia severity increased the prevalence risk of all individual depression symptoms between 8 and 15%, while sleep duration increased the prevalence risk of appetite dysregulation (PR 1.86, p < 0.001), fatigue (PR 1.51, p < 0.001), difficulty concentrating (PR 1.61, p = 0.003), feelings of failure (PR 1.58, p = 0.002), and suicidal behavior (PR 2.54, p = 0.01). The interaction of sleep duration and insomnia was negative and ranged between 3 and 6%. In clinically significant depression (PHQ >=10), only insomnia severity increased the prevalence risk of depression severity (PR 1.02, p = 0.001). Insomnia and short sleep predict prevalent depression, but their interactive effect was negative. Thus, while insomnia had a greater association with depression severity and symptoms, this association was dependent on habitual sleep duration.