Examining the influence of episode number and age of onset on individual depressive symptoms across episodes of major depression

Major depression is characterized by an episodic course with symptom manifestations differing across episodes. Previous work has found that symptom presentation differs across age. However, studies of symptom presentation have largely focused on symptoms in individual episodes, requiring further investigation of longitudinal symptom change. This study explored the impact of the initial age of onset, the number of episodes, and age of onset of each episode on individual depressive symptoms, while accounting for episode severity. We used data from the Oregon Adolescent Depression Project (N = 629) examining participants with at least one major depressive episode, assessed by diagnostic interview, across a 15-year follow-up. Multilevel logistic regression models revealed that approximately 20–25% of the main effects were significant and some were qualified by cross-level interactions. However, only a few associations remained robust after correcting for multiple comparisons. Specifically, older initial age of onset was associated with fatigue, younger initial age of onset for the first episode was associated with suicidal ideation, and a lower episode number was associated with weight loss. These findings highlight potential initial age of onset and scar effects influencing symptom manifestation, but require replication.