Subsyndromal depression in the United States: prevalence, course, and risk for incident psychiatric outcomes

Background Subsyndromal depression (SD) may increase risk for incident major depressive and other disorders, as well as suicidality. However, little is known about the prevalence, course, and correlates of SD in the US general adult population. Method Structured diagnostic interviews were conducted to assess DSM-IV Axis I and II disorders in a nationally representative sample of 34 653 US adults who were interviewed at two time-points 3 years apart. Results A total of 11.6% of US adults met study criteria for lifetime SD at Wave 1. The majority (9.3%) had <5 total symptoms required for a diagnosis of major depression; the remainder (2.3%) reported ⩾5 symptoms required for a diagnosis of major depression, but denied clinically significant distress or functional impairment. SD at Wave 1 was associated with increased likelihood of developing incident major depression [odds ratios (ORs) 1.72–2.05], as well as dysthymia, social phobia, and generalized anxiety disorder (GAD) at Wave 2 (ORs 1.41–2.92). Among respondents with SD at Wave 1, Cluster A and B personality disorders, and worse mental health status were associated with increased likelihood of developing incident major depression at Wave 2. Conclusions SD is prevalent in the US population, and associated with elevated rates of Axis I and II psychopathology, increased psychosocial disability, and risk for incident major depression, dysthymia, social phobia, and GAD. These results underscore the importance of a dimensional conceptualization of depressive symptoms, as SD may serve as an early prognostic indicator of incident major depression and related disorders, and could help identify individuals who may benefit from preventive interventions.