Reduction in Rates of Stressful Life Events Preceding Depressive Episodes in the Course of Recurrent Major Depressive...

Stressful life events (SLEs) are a well-established etiologic risk factor for major depressive disorder (MDD). The kindling hypothesis proposes that their role diminishes as episodes recur, with illness becoming progressively autonomous from environmental triggers. It remains unclear whether this reflects true within-person change or a compositional shift-whereby more highly recurrent patients are those whose episodes were stress-independent from the outset.

We analyzed data from life history calendars, a structured method for reconstructing lifetime sequences of depressive episodes and antecedent life events, from 5843 Korean women with recurrent MDD (≥ 2 lifetime episodes) contributing 17,338 episode observations (KOMOGEN-D), with replication in 708 Chinese women contributing 1905 episode observations (CONVERGE).

Consistent with the kindling hypothesis, the proportion of episodes preceded by any SLE declined substantially and monotonically across episode order, from 94.8% (95% CI, 94.2%-95.4%) at the first episode to 77.7% (95% CI, 71.2%-84.2%) at the seventh (OR per episode increase, 0.66; 95% CI, 0.62-0.71). Inter-episodic intervals shortened with episode order (β = -1.50 years; 95% CI, -1.61 to -1.38), indicating that episodes became more frequent. Within-individual analyses revealed that more participants had decreasing than increasing SLE counts across episodes, with more frequent transitions from SLE-associated to non-SLE-associated episodes than the reverse. Stratification by SLE type showed that independent SLEs decreased across episodes, whereas dependent SLEs increased. The main findings were replicated in CONVERGE, although some within-person transition analyses were limited by smaller sample size.

Across two large cohorts collected in different cultural settings, SLE involvement preceding episodes decreased across episode order while the rate of recurrence accelerated, and within-person analyses supported stress-episode decoupling as an individual-level process. These findings provide some of the strongest evidence yet assembled that the course of recurrent MDD is consistent with the kindling hypothesis: episodes become progressively less dependent on external stressors, shifting toward a more autonomous illness. These results have direct implications for stratifying recurrence risk by episode stage and for identifying the point in the illness course at which preventive strategies should shift emphasis from targeting environmental stressors toward sustained pharmacological or psychological relapse prevention.