Depression follows seasonal patterns in some people, new Swedish study shows
Researchers tracking over 4,800 adults for two years found that depression isn't always stable—for some people, symptoms worsen predictably in summer or winter, while their self-care habits collapse during those periods. The finding could reshape how employers and health systems support workers and design preventative interventions.
Originaltitel: Depression symptom trajectories and self-care variability over the year in 4801 Swedish adults
<p>Depression is heterogeneous in severity and symptom dynamics. This study tested 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 a measure of depression (PHQ-9; 30,740 observations) and quarterly 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 between seasonal classes. The Summer-worsening class declined in daily rhythm, sleep sufficiency, and leisure activities during summer. The Winter-worsening class showed milder declines but in winter, additionally including reduced exercise. Self-care was relatively stable across the year in the Stable classes, with especially clear difference between classes in sleep sufficiency, daily rhythm, exercise, and leisure activities. Within-person analyses showed that months with higher-than-usual depression coincided with poorer-than-usual daily rhythm, hygiene, sleep sufficiency, and 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 persistently severe depression, core self-care behaviours (sleep, daily rhythm, social and leisure engagement) remain priority treatment targets year-round.</p>