Life course socioeconomic positions (SEP) and their association with the trajectory of depressive symptoms from mid to later adult life: Korean Longitudinal Study of Ageing (KLoSA)

Socioeconomic adversity across the life course can shape mental health in later life. This thesis examines the relationship between life course socioeconomic position (SEP) and trajectories of depressive symptoms in older Korean adults, using data from the Korean Longitudinal Study of Ageing (KLoSA). The analysis applies life course models - critical/sensitive period, cumulative disadvantage, and social mobility, to test how socioeconomic conditions at different life stages affect late-life depressive symptoms risk. SEP was measured at five key life points (father’s education in early life; own education in young adulthood; occupations at ages 30 and 40 in mid-life; and current occupation in later life). Depressive symptoms were assessed by the CES-D 10 scale. Cross-sectional logistic regression (2006 baseline) and multilevel growth curve modelling (2006–2020) were used, stratified by sex and cohort. The findings show that adult SEP, especially one’s own education and current occupational status, emerge as the most robust correlates of depressive symptoms, whereas early-life SEP alone is a weaker predictor once later life SEP is accounted for. Cumulative socioeconomic disadvantage across multiple life stages exhibits a dose–response relationship with higher depressive symptom levels in later life. In addition, individuals who experienced upward mobility (improved SEP over time) tend to have fewer depressive symptoms, although this does not fully offset the negative impact of early disadvantage. Cohort differences suggest that younger women had more similar earlylife SEP to their male-counterparts (indicating some convergence), yet pronounced disparities in mid- and later life SEP persist, sustaining inequalities in depression.