Loneliness as an active ingredient in preventing or alleviating youth anxiety and depression: a critical interpretative synthesis incorporating principles from rapid realist reviews.

Loneliness is a relatively common problem in young people (14-24 years) and predicts the onset of depression and anxiety. Interventions to reduce loneliness thus have significant potential as active ingredients in strategies to prevent or alleviate anxiety and depression among young people. Previous reviews have focused on quantitative evidence and have not examined potential mechanisms that could be targets for intervention strategies. To build on this work, in this review we aimed to combine qualitative and quantitative evidence with stakeholder views to identify interventions that appear worth testing for their potential effectiveness in reducing loneliness, anxiety and depression in young people aged 14-24 years, and provide insights into the potential mechanisms of action. We conducted a Critical Interpretative Synthesis, a systematic review method that iteratively synthesises qualitative and quantitative evidence and is explicitly focused on building theory through a critical approach to the evidence that questions underlying assumptions. Literature searches were performed using nine databases, and eight additional databases were searched for theses and grey literature. Charity and policy websites were searched for content relevant to interventions for youth loneliness. We incorporated elements of Rapid Realistic Review approaches by consulting with young people and academic experts to feed into search strategies and the resulting conceptual framework, in which we aimed to set out which interventions appear potentially promising in terms of theoretical and empirical underpinnings and which fit with stakeholder views. We reviewed effectiveness data and quality ratings for the included randomised controlled trials only. Through synthesising 27 studies (total participants n = 105,649; range 1-102,072 in different studies) and grey literature, and iteratively consulting with stakeholders, a conceptual framework was developed. A range of 'Intrapersonal' (e.g. therapy that changes thinking and behaviour), 'Interpersonal' (e.g. improving social skills), and 'Social' Strategies (e.g. enhancing social support, and providing opportunities for social contact) seem worth testing further for their potential to help young people address loneliness, thereby preventing or alleviating depression and/or anxiety. Such strategies should be co-designed with young people and personalised to fit individual needs. Plausible mechanisms of action are facilitating sustained social support, providing opportunities for young people to socialise with peers who share similar experiences, and changing thinking and behaviour, for instance through building positive attitudes to themselves and others. The most convincing evidence of effectiveness was found in support of Intrapersonal Strategies: two randomised controlled studies quality-rated as 'good' found decreases in loneliness associated with different forms of therapy (Cognitive Behavioural Therapy or peer network counselling), although power calculations were not reported, and effect sizes were small or missing. Strategies to address loneliness and prevent or alleviate anxiety and depression need to be co-designed and personalised. Promising elements to incorporate into these strategies are social support, including from peers with similar experiences, and psychological therapy.