title: Depression and generalized anxiety disorder: cumulative and sequential comorbidity in a birth cohort followed prospectively to age 32 years.
abstract: BACKGROUND
  The close association between generalized anxiety disorder (GAD) and major depressive disorder (MDD) prompts questions about how to characterize this association in future diagnostic systems. Most information about GAD-MDD comorbidity comes from patient samples and retrospective surveys.
  
  
  OBJECTIVE
  To revisit the sequential and cumulative comorbidity between GAD and MDD using data from a prospective longitudinal cohort.
  
  
  METHODS
  Prospective longitudinal cohort study.
  
  
  METHODS
  New Zealand.
  
  
  METHODS
  The representative 1972-1973 Dunedin birth cohort of 1037 members was followed up to age 32 years with 96% retention.
  
  
  METHODS
  Research diagnoses of anxiety and depression were made at ages 11, 13, 15, 18, 21, 26, and 32 years. Mental health services were reported on a life history calendar.
  
  
  RESULTS
  Sequentially, anxiety began before or concurrently in 37% of depression cases, but depression began before or concurrently in 32% of anxiety cases. Cumulatively, 72% of lifetime anxiety cases had a history of depression, but 48% of lifetime depression cases had anxiety. During adulthood, 12% of the cohort had comorbid GAD + MDD, of whom 66% had recurrent MDD, 47% had recurrent GAD, 64% reported using mental health services, 47% took psychiatric medication, 8% were hospitalized, and 11% attempted suicide. In this comorbid group, depression onset occurred first in one third of the participants, anxiety onset occurred first in one third, and depression and anxiety onset began concurrently in one third.
  
  
  CONCLUSIONS
  Challenging the prevailing notion that generalized anxiety usually precedes depression and eventually develops into depression, these findings show that the reverse pattern occurs almost as often. The GAD-MDD relation is strong, suggesting that the disorders could be classified in 1 category of distress disorders. Their developmental relation seems more symmetrical than heretofore presumed, suggesting that MDD is not necessarily primary over GAD in diagnostic hierarchy. This prospective study suggests that the lifetime prevalence of GAD and MDD may be underestimated by retrospective surveys and that comorbid GAD + MDD constitutes a greater mental health burden than previously thought.
authors.affiliation: Institute of Psychiatry, King's College London, De Crespigny Park, London SE5 8AF, UK. t.moffitt@iop.kcl.ac.uk
authors.forename: Terrie E
authors.initials: TE
authors.lastname: Moffitt
authors.forename: HonaLee
authors.initials: H
authors.lastname: Harrington
authors.forename: Avshalom
authors.initials: A
authors.lastname: Caspi
authors.forename: Julia
authors.initials: J
authors.lastname: Kim-Cohen
authors.forename: David
authors.initials: D
authors.lastname: Goldberg
authors.forename: Alice M
authors.initials: AM
authors.lastname: Gregory
authors.forename: Richie
authors.initials: R
authors.lastname: Poulton
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D017668:Age of Onset; D001008:Anxiety Disorders / Q000175:diagnosis / Q000453:epidemiology*; D002648:Child; D015897:Comorbidity; D003865:Major Depressive Disorder / Q000175:diagnosis / Q000453:epidemiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008605:Mental Health Services / Q000706:statistics & numerical data; D009520:New Zealand / Q000453:epidemiology; D015995:Prevalence; D011446:Prospective Studies; D017678:Sex Distribution; D012737:Sex Factors; D013406:Suicide, Attempted / Q000706:statistics & numerical data