Mental Health Antecedents and Correlates of 2 Distinct Developmental Pathways to Suicidal Ideation

Importance Suicidal ideation is increasingly common in youth. Trajectories and associated mental health symptoms across development remain poorly understood. Objective To describe trajectories of suicidal ideation from early adolescence to young adulthood and identify preceding and co-occurring mental health symptoms to inform optimal prevention. Design, Setting, and Participants This cohort study used data from a contemporary, longitudinal cohort study, the Québec Longitudinal Study of Child Development (QLSCD), including reports from participants, parents, and teachers. The QLSCD is a population-based birth cohort study of 2120 singletons born between 1997 and 1998 in Québec, Canada, and followed up to age 25 years (2023). Data were analyzed from September 2024 to February 2025. Main Outcomes and Measures Serious suicidal ideation in the past 12 months was assessed by a question to participants at ages 13, 15, 17, 20, 23, and 25 years. Exposures Mental health symptoms (eg, internalizing, externalizing) as reported by parents, teachers, and self-reports on validated questionnaires and standardized across 5 developmental periods: preschool (3-5 years), childhood (6-12 years), early adolescence (13 years), mid-late adolescence (15-17 years), and young adulthood (20-25 years). Results A total of 1635 participants (845 female [51.7%]; participant number is weighted to account for selective attrition) provided answers on suicidal ideation, with survey weights applied. A total of 3 trajectories were identified: minimal/no ideation (1433 [87.6%]), onset in early adolescence (117 [7.1%]), and onset in young adulthood (86 [5.2%]). Relative to minimal/no ideation, onset in early adolescence was associated with elevated symptoms across nearly all mental health indicators from childhood through adulthood. This included both internalizing (eg, childhood depressive symptoms: risk ratio [RR], 1.75; 95% CI, 1.45-2.05) and externalizing (eg, childhood disruptive symptoms: RR, 1.60; 95% CI, 1.29-1.91) symptoms and maternal antisocial symptoms (RR, 1.39; 95% CI, 1.11-1.66). In contrast, onset of suicidal ideation in young adulthood was associated with internalizing symptoms (eg, mid-late adolescence depressive symptoms: RR, 1.84; 95% CI, 1.28-2.39) emerging in adolescence and worsening mental distress in young adulthood. Conclusions and Relevance Results of this cohort study revealed 2 pathways to suicidal ideation: onset in early adolescence, with persistent childhood internalizing/externalizing symptoms, and onset in young adulthood linked to internalizing symptoms emerging in adolescence without prior distress. Findings suggest timely addressing of mental health symptoms and developmental stage-specific prevention.