Sociodemographic and Lifestyle Factors Associated with Adolescent Mental Ill-Health: a Decision Tree Analysis.

Mental ill-health is a leading contributor to adolescent disease burden, with females and socioeconomically disadvantaged youth facing higher rates of mental disorders. Adolescence is a key period for the development of lifestyle risk factors for mental disorder, which are increasingly being recognized as important and novel population-level preventive intervention targets. We used decision trees to examine combinations of sociodemographic factors and the "big six" lifestyle behaviours (poor sleep, physical inactivity, sedentary screen time, poor diet, alcohol use and smoking) prospectively associated with worse anxiety, depression and psychological distress scores. We examined survey data from 3978 Australian adolescents (mean age 14.6 at baseline) who participated in the Health4Life study in 2021 and 2022. CART decision trees were run to rank the relative importance of each risk factor and to identify combinations of risk factors that characterize groups with highest anxiety (PROMIS-AP), depression (PHQ-8A) and psychological distress (K6) scores 1 year later. Gender was the primary differentiator of risk, with cisgender females and gender diverse adolescents having consistently worse mental ill-health scores than cisgender males. Inadequate sleep and excessive sedentary recreational screen time were consistently the top lifestyle factors and often emerged in combination to characterize higher risk groups. These findings offer new insights into relative importance of various lifestyle risk factors in adolescent mental health and highlight both the increased risk from engaging in combinations of unhealthy lifestyle behaviours and the need for targeted prevention and early intervention initiatives to reduce the gender gap in adolescent mental health.