Sustained High-Loneliness States in Persistent Depressive Disorder: An Ecological Momentary Assessment Study

Loneliness is a risk factor for mental disorders. While transient loneliness states are thought to serve as an adaptive signal motivating social reconnection, elevated loneliness states that persist may turn maladaptive. Yet, how the level and persistence of loneliness states differ among individuals with and without mental disorders remains unclear. We used ecological momentary assessment (EMA) to characterize state loneliness in inpatients with persistent depressive disorder (PDD; n = 58) and in healthy controls (HCs; n = 42), deriving two theoretically motivated indices: mean level and duration of high-loneliness states. Trait loneliness (UCLA Loneliness Scale) and recalled early adversity (Childhood Trauma Questionnaire; emotional neglect and abuse) were also assessed. As hypothesized, inpatients with PDD reported higher mean state loneliness and longer high-loneliness states, lasting 3.5 consecutive prompts on average. Inpatients with PDD were also less likely to leave a high-loneliness state at the next assessment, adjusted for current level of loneliness. State emotional isolation (the momentary perception of lacking people to turn to) emerged as the most consistent correlate of trait loneliness and was associated with recalled emotional neglect. These exploratory findings suggest that early emotional adversity may contribute to emotional isolation in daily life and, in turn, to trait loneliness in PDD, requiring prospective testing.