Depression symptom trajectories and self-care variability over the year in 4801 Swedish adults.

Depression is heterogeneous in severity and symptom dynamics. The present study examined whether distinct within-year trajectories of depression symptoms exist and how they relate to self-care behaviours. In this longitudinal study, 4801 individuals (Mage = 35.6 years, 18-81 years, 72.7% women) completed monthly assessments of depression (PHQ-9; 30,740 observations) and quarterly assessments on self-care behaviours (sleep and rhythm, leisure and activity, nutritional aids, social activities, and substance use) (9296 observations) between July 2020-June 2022. Growth mixture modelling identified five depression trajectories: three stable classes - Mild (n = 1419, 29.6%), Moderate (n = 1463, 30.5%), Severe (n = 1587, 33.1%) - and two seasonal classes - Winter-worsening (n = 215, 4.5%) and Summer-worsening (n = 117, 2.4%). Generalized additive mixed effect models showed marked within-year changes in self-care among the seasonal classes. The Summer-worsening class declined in daily rhythm, sleep sufficiency, and enjoyment of leisure activities during summer. The Winter-worsening class showed milder declines but during winter, and additionally included reduced physical exercise. Self-care behaviours remained relatively stable across the year in the Stable classes, with especially clear between-class differences in sleep sufficiency, daily rhythm, exercise, and enjoyment of leisure activities. Within-person analyses showed that months with higher-than-usual depression coincided with poorer-than-usual daily rhythm, hygiene, sleep sufficiency, and enjoyment of leisure activities. These patterns point to pragmatic, time-sensitive targets, where promoting stable routines in areas of sleep, leisure, and physical activities ahead of peaks may help prevent symptom escalation. For individuals with persistently severe depression, core self-care behaviours (sleep, daily rhythm, social engagement and enjoyment of leisure activities) remain priority treatment targets year-round.