Reducing recreational screen-time in adolescents: the 'Switch-off 4 Healthy Minds' randomised controlled trial

Research Doctorate - Doctor of Philosophy (PhD)Background: Secular decreases in physical activity and increases in recreational screen-time among young people are cause for concern. Both physical inactivity and excessive recreational screen-time are independently associated with poor physical, social and psychological health in adolescence. As adolescence marks a key period for establishing health behaviours, there is a need to identify effective and scalable interventions to address both physical inactivity and excessive recreational screen-time. Although an abundance of interventions have been conducted to increase young people’s physical activity, fewer studies have examined the impact of interventions designed to reduce recreational screen-time, especially in adolescent populations. Of those studies that have examined screen-time reduction in young people, few interventions have been designed to be ‘scalable’ or adopted a theoretical framework to assist in the identification of behaviour change mechanisms. Thesis objectives: Presented as a series of studies, this thesis by publication aims to address current gaps in the literature. The principal focus of this thesis is the development and evaluation of the ‘Switch-off 4 Healthy Minds’ (S4HM) intervention, which was evaluated using a cluster randomised controlled trial (RCT) in a sample of Australian adolescents. Further, this thesis presents a series of related studies investigating secondary aims, which are briefly described below. Given the chronology of the research included within this thesis, and the importance of providing context to the primary aim, the Secondary aims will be presented first and are listed in order below. <i>Secondary aim 1: Review the evidence of associations between physical activity, screen-time and mental health outcomes in adolescents</i> The aim of this chapter was to examine associations between health behaviours (i.e., physical activity and recreational screen-time) and indicators of mental health among adolescents. The original objective was to conduct a novel systematic review of studies that had examined the association between recreational screen-time and self-concept. However, as too few studies were identified in the preliminary search, an alternate systematic review focused on physical activity and physical self-concept (general and sub-domains) was conducted. Included studies were identified through a structured search of six electronic databases with no date restrictions. In total, 111 studies were qualitatively and 64 were quantitatively synthesised. Potential moderators examined included; sex, age and study design. Perceived competence was most strongly associated with physical activity (r = 0.30, 95% CI = 0.24 to 0.35, p < 0.001), followed by perceived fitness (r = 0.26, 95% CI = 0.20 to 0.32, p < 0.001), general physical self-concept (r = 0.25, 95% CI = 0.16 to 0.34, p < 0.001) and perceived physical appearance (r = 0.12, 95% CI = 0.08 to 0.16, p < 0.001). Sex was a significant moderator for general physical self-concept and age for perceived appearance as well as perceived competence. No significant moderators were found for perceived fitness. Overall, significant associations of a medium effect size were present between general physical self-concept, perceived competence, perceived fitness and physical activity in young people. <i>Secondary aim 2: To provide a rationale and present the study protocol for the ‘Switch-off 4 Healthy Minds’ (S4HM) intervention: A cluster randomised controlled trial to reduce recreational screen-time in adolescents</i> The aim of chapter 3 was to describe the methods used in the S4HM intervention and to provide justification for the examination of each outcome. The primary outcome of the S4HM intervention was recreational screen-time. Secondary outcomes consisted of mental health indicators including; physical self-concept, psychological well-being, psychological difficulties and psychological distress. Objectively measured physical activity (accelerometry), body mass index (BMI) and hypothesised mediators of behaviour change (autonomous motivation, controlled motivation, and amotivation) were explored. The 6-month multi-component intervention was designed to encourage adolescents to manage their recreational screen-time using a range of evidence-based strategies. Grounded in Self-determination Theory (SDT), the S4HM intervention included the following components: an interactive seminar for students, eHealth messaging, behavioural contract and parental newsletters. This chapter highlighted the lack of screen-time interventions among adolescents and projected future research was needed to determine if reducing screen-time aids the prevention and treatment of physical inactivity and mental health in youth. <i>Secondary aim 3: To examine longitudinal associations between changes in screen-time and mental health outcomes in adolescents</i> The aim of this chapter was to explore longitudinal associations between changes in recreational screen-time (both total and device specific) and mental health outcomes (mental well-being and ill-being) in a sample of Australian adolescents. A subsequent aim was to examine the association between non-recreational screen-time (computer use for homework) and mental health. Recreational screen-time (television, DVD, computer, tablet and mobile phone use), non-recreational screen-time and mental health indicators (physical self-concept, psychological well-being and psychological difficulties) were reported on two occasions (Time 1 and Time 2) over the first year of secondary school. After adjusting for relevant covariates (Time 1 measurements, group allocation, school clustering, sex, socio-economic status, Time 1 body mass index (BMI) and Time 1 physical activity), multi-level linear mixed models were conducted. Changes in total recreational screen-time (β = -.09 p = .048) and tablet/phone use (β = -.18, p < .001) were negatively associated with physical self-concept. Changes in total recreational screen-time (β = -.20, p = .001) and computer use (β = -.23, p = .003) were negatively associated with psychological well-being. A positive association was found with television/DVD use and psychological difficulties (β = .16, p = .015). No associations were found between indicators of mental health and screen use for homework purposes. Findings suggest different devices have distinct associations with mental health outcomes. While this study did not provide causal evidence for the detrimental effect of screen-time on mental health, findings suggest reducing screen-time may improve mental health in young people. <i>Primary aim 1: To evaluate the effects of the S4HM intervention by examining outcomes and potential mediators in a cluster RCT</i> The aim of this chapter was to evaluate the impact of the S4HM intervention in adolescents. The primary outcome was recreational screen-time and secondary outcomes included mental health indicators, physical activity, and BMI. Eligible participants reported exceeding recreational screen-time recommendations (i.e., > 2 hours/day). In total, 322 adolescents (mean age = 14.4 ± 0.6 years) from eight secondary schools in New South Wales, Australia were recruited. The S4HM intervention was a cluster RCT with study measures at baseline and 6-months (post-intervention). Outcome analyses were conducted using linear mixed models. Meditation analyses were conducted to determine if changes in motivation mediated the intervention effect using a product-of-coefficient test. At post intervention, significant reductions in screen-time occurred in both groups, with a greater reduction observed in the intervention group (-50 min/day versus -29 minutes, p <.05 for both). However, the adjusted difference in change between groups was not statistically significant (mean = -21.3 min/day, p = 0.255). There were no significant intervention effects for mental health outcomes, physical activity or BMI. It was found that the intervention effect was partially mediated by increases in autonomous motivation to limit screen-time but not controlled motivation