Optimising a digital parent-based intervention to improve adolescent health risk behaviours in families living in socio-economically disadvantaged communities: findings from the Health4Life Parents & Teens factorial randomised trial.

BACKGROUND

Adolescence is a critical period when health risk behaviours contributing to long-term disease burden emerge. Parent-based interventions show promise, yet engagement is often low and few exist for socioeconomically disadvantaged communities. We applied the Multiphase Optimisation Strategy (MOST) to identify a maximally effective, minimally burdensome digital intervention to support parents to improve adolescent health risk behaviours.

METHODS

A 2 × 2 × 2 × 2 factorial randomised trial was conducted with parents of adolescents (aged 11-15 years), living in a disadvantaged area of New South Wales, Australia (quintiles 1-2, Index of Relative Socio-economic Disadvantage). Participants were recruited via social media and in community settings and randomised to 1 of 16 experimental conditions via a Blockrand-generated scheme in R. All participants received access to six online modules targeting key health risk behaviours (core component). Four components were experimentally tested (present vs absent): text messages, tailored feedback, stress management training, and telehealth coaching, resulting in 16 possible intervention combinations. Participants and researchers were not masked to allocation. The primary outcome was 3-month change in parental encouragement of adolescent health habits (Health Habits subscale of Parenting to Reduce Adolescent Depression Anxiety Scale; possible range 0-12). Parent-reported perceived effort of completing each component was examined (5-point scale: 'no effort at all' to 'huge effort'). The trial was prospectively registered (ACTRN12624001492549; 20/12/2024).

FINDINGS: Between April 23 and October 22 2025, we recruited and randomised 303 participants. One withdrew after randomisation, and ten were removed during analysis, resulting in 292 parents at baseline and 231 (79%) at follow-up. Tailored feedback (B = 0.21, p = 0.054, mean difference = 0.42, 95% CI = -0.01 to 0.85, Cohen's d = 0.26) and telehealth coaching (B = 0.31, p = 0.0051, mean difference = 0.62, 95% CI = 0.19 to 1.04, Cohen's d = 0.38) improved parental encouragement, while text messages had a negative effect (B = -0.33, p < 0.0026, mean difference = -0.66, 95% CI = -1.09 to -0.23, Cohen's d = -0.41). Telehealth coaching yielded the greatest improvements, but highest perceived effort (mean = 2.4/5, SD = 1.2). Tailored feedback achieved comparable gains, with significantly lower effort (mean = 2.1/5, SD = 1.0; p = 0.03). The optimised intervention comprised online modules and tailored feedback. No adverse events were reported.

INTERPRETATION: Using a highly efficient MOST factorial design, we identified a low-burden, highly scalable intervention for parents living in disadvantaged communities, ready for evaluation in a definitive randomised controlled trial.

FUNDING: Medical Research Future Fund (2021535).