Objective. The progression to depression in children with attention-deficit/hyperactivity disorder (ADHD) is not clearly understood. To clarify this relationship, we tested the following hypotheses in a population-based study: (1) children with ADHD have a higher risk of developing depression than children without ADHD; (2) the pathway from ADHD to depression is mediated (partly) through anxiety and disruptive behavior disorders; and (3) mediation through anxiety is more prevalent in girls, and mediation through disruptive behavior disorders is more prevalent in boys. Method. From October 2008 to September 2010, the Composite International Diagnostic Interview was used to assess ADHD, major depressive episodes, anxiety disorders, and disruptive behavior disorders in 1,584 participants from the TRacking Adolescents' Individual Lives Survey (TRAILS) cohort. Cox regression was used to model the effects of ADHD, anxiety, and disruptive behaviors on depression. Risk of and pathways to depression were studied in both children with ADHD and children with subthreshold ADHD. Results. Comorbid depression was present in 36% of children with a diagnosis of ADHD, 24% of children with subthreshold ADHD, and 14% of children with no ADHD. Anxiety and disruptive behaviors mediated 32% of depression in ADHD. Pathways through anxiety and disruptive behavior disorders were independent of gender. Disruptive behavior disorder was a stronger mediator than anxiety for both genders (all P < .01). Conclusions. These findings may help forewarn of impending depression and therefore allow opportunities for interventions when comorbid anxiety and/or disruptive behavior disorders are present in a child with ADHD.
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