LAUSR

Purpose Identifying and understanding modifiable risk and protective factors that can inform early detection and intervention to prevent adolescent emotional problems and harmful behaviours is among the most pressing modern-day public health challenges. This paper describes the rationale, objectives, methods, and anticipated outcomes of the LIFECOURSE study, a multi-level, bio-psychosocial prospective study designed to advance our understanding of factors that shape adolescent mental health and behaviour. Methods Conducted by the Icelandic Centre for Social Research and Analysis at Reykjavik University, LIFECOURSE is a longitudinal population-based developmental study of Icelandic adolescents born in 2004. The study utilizes a comprehensive multi-informant assessment of individual, societal and biological factors measured across the lifespan. Data assembly and collection were conducted from 2016–2020 and utilize both retrospective and prospective data sources: (a) retrospective registry data assembled from seven national databases, (b) prospectively collected social surveys and (c) biomarker samples. Results Of the 3914 eligible adolescents, 60.8% ( n  = 2378) provided informed parental consent and student assent to participate in the study, with approximately half of the participants being female ( n  = 1175, 49.4%) and the majority being born in the capital area ( n  = 1455; 61.2%). The coverage of available data from the national databases and participation in the social surveys ranged from 81.7 to 100%. Conclusions Major gaps remain in our knowledge of how individual, societal and biological factors across the lifespan—from early life to adolescence—interact and shape the risk for emotional problems and harmful behaviours during adolescence. The LIFECOURSE study was designed to address this knowledge gap.