Adolescent behavioural intentions: Secondary outcomes from a cluster randomized controlled trial of the Health4Life school-based lifestyle modification intervention.

Intervention: Health4Life: a school-based eHealth intervention targeting multiple health behaviour change (MHBC).

Research question: Does Health4Life impact secondary outcomes of self-reported intentions regarding six lifestyle behaviours in adolescents (alcohol use, tobacco smoking, screentime, physical activity, discretionary beverage consumption, and sleep)?

Methods: We implemented a cluster randomized controlled trial within secondary schools across three Australian states. Schools were randomly assigned (1:1) to receive either the Health4Life intervention, which consisted of a six-module, web-based program and accompanying smartphone app, or an active control (standard health education). Randomization was stratified by site and school gender composition (using Blockrand in R). All students aged 11-13 years who attended the participating schools and were fluent in English were eligible. Students completed self-report questionnaires at baseline, post-intervention, 12 months, and 24 months. Outcomes were intentions to try alcohol, try tobacco, reduce screentime, engage in physical activity on most or all days, swap discretionary beverages for water, and meet sleep guidelines. Mixed effects models estimated between-group differences in the outcomes over 24 months.

Results: Immediately post-intervention, Health4Life significantly reduced intentions to try alcohol and tobacco and increased intentions for longer sleep and reduced screentime compared to control. Intervention effects on screentime intentions persisted at 12 months but not at 24 months. No lasting effects were observed on intentions for physical activity or discretionary beverage consumption.

Conclusion: Health4Life shows promise in influencing adolescent intentions across various MHBC areas, especially immediately after intervention. However, further investigation is needed to sustain these intention changes beyond short term to facilitate behaviour change.