Clustering of Unhealthy Lifestyle Behaviours and Its Contextual Determinants in Adolescents: A Multilevel Analysis of School-Based Surveys in 45 Countries

<b>Background:</b> This study examined the clustering of unhealthy lifestyle behaviours and their determinants among adolescents across Europe, Central Asia, and North America. <b>Methods:</b> The study included 210,713 adolescents aged 11 to 15 years from 45 countries who participated in the 2018 Health Behaviour in School-aged Children (HBSC) study. Lifestyle behaviours, including physical inactivity, inadequate fruit and vegetable consumption, frequent soft drink consumption, alcohol use, and smoking, were used to examine the clustering of unhealthy behaviours. Multilevel mixed-effects logistic regression was employed to assess the associations between unhealthy behaviour clustering (≥3 unhealthy behaviours) and contextual factors at the individual, family, and school levels. <b>Results:</b> A high prevalence of clustered unhealthy behaviours was observed among adolescents, with 51.5% engaging in three or more unhealthy lifestyle behaviours. The odds increased with age (AOR: 1.79, 95% CI: 1.75, 1.84 for those aged ≥ 15 years), among males (AOR: 1.26, 95% CI: 123, 1.28), and among those experiencing higher academic pressure (AOR: 1.13, 95% CI: 1.09, 1.17 for very high academic pressure). In contrast, the odds were lower among adolescents from a higher family affluence background (AOR: 0.62 95% CI: 0.60, 0.65 for high), among adolescents living with both parents (AOR: 0.83, 95 CI: 0.81, 0.85), those reporting higher family support (AOR: 0.62, 95% CI: 0.60, 0.63 for high), higher peer support at school (AOR: 0.87, 95% CI: 0.84, 0.89 for high), and those reporting higher school satisfaction (AOR: 0.50, 95% CI: 0.48, 0.52 for very high). <b>Conclusions</b>: The study reveals that one in two adolescents engages in three or more unhealthy lifestyle behaviours. It emphasises the need to tackle this public health challenge through multisectoral interventions targeting individual-level and contextual factors at the family and school levels.