How adolescent depressive symptoms are associated with premature mortality: Behavioral and socioeconomic pathways across the life course.

Premature mortality in young adulthood has become a growing public health concern in the United States, yet it remains unclear whether vulnerability to early death originates as early as adolescence. Although depressive symptoms are highly prevalent during adolescence and linked to long-term health and socioeconomic disadvantages, their prospective association with premature mortality remains poorly understood. This study examined whether depressive symptoms experienced during adolescence predict premature mortality in young adulthood and whether health behaviors and socioeconomic status in early adulthood help explain this association. Data were drawn from Waves I and III of the National Longitudinal Study of Adolescent to Adult Health, along with the Mortality Outcomes Surveillance System established in Wave V (N = 14,320). Cox proportional hazards models estimated the association between adolescent depressive symptoms and premature mortality, and cause-specific Cox proportional hazards models evaluated deaths due to disease, suicide, and external causes. Mediation analyses tested health behaviors and socioeconomic factors as mechanisms. Higher adolescent depressive symptoms were associated with increased risk of all-cause premature mortality in young adulthood. Cause-specific models showed that this association was concentrated in deaths due to external causes, with no significant associations for disease-related deaths or suicide. Cigarette smoking, marijuana use, lower educational attainment, and reduced employment in early adulthood accounted for part of the association for all-cause mortality. For external-cause mortality, however, health behaviors-specifically cigarette smoking and marijuana use-emerged as the prominent mediating pathways. Findings suggest that adolescent depressive symptoms may be associated with an increased vulnerability to premature mortality, in part through behavioral and socioeconomic pathways that emerge in early adulthood. Strengthening early mental health identification and support could reduce long-term disparities in survival.