Social connection interventions and depression in young adults: a systematic review and meta-analysis

The study addresses whether social connection interventions can reduce depression and improve social connection or reduce loneliness among young adults (18–24 years) in the general population. Early adulthood is marked by developmental transitions and societal changes (e.g., mobility, technology) that heighten vulnerability to loneliness and depression. Loneliness strongly predicts adverse mental health, including depression, and has increased over decades, with young adults particularly affected, notably during the COVID-19 pandemic. Despite the link between social connection and mental health, most intervention research targets children/adolescents, older adults, or clinical populations, leaving a gap for non-clinical young adults. This review aims to identify social connection/loneliness interventions for young adults and evaluate their effectiveness on depression and social connection/loneliness outcomes.

Background evidence shows a robust association between loneliness and depression, with loneliness in young adults predicting later antidepressant use and poorer outcomes. Loneliness peaks in younger and older age groups and has increased among emerging adults over time; pandemic-era studies reported larger rises in loneliness and depression among young adults than other ages. Social capital is protective against depression, yet intervention literature has focused mainly on youth in school settings, older adults, or clinical samples. Existing school-based mental health promotion work suggests educational settings can be viable for implementation, but there is limited evidence specific to 18–24-year-olds in general populations, pointing to an important gap this review seeks to address.

Design: Systematic review and meta-analysis following PRISMA, pre-registered on PROSPERO (CRD42023395595). Data sources: PubMed, Scopus, PsycInfo; English-language studies from 01/01/2000 to 01/01/2023 using terms related to young adults, social interventions/connectedness, depression, and RCTs. Eligibility: Quantitative peer-reviewed studies including 18–24-year-olds from the general population; interventions explicitly aiming to increase social connections or reduce loneliness (in-person or online); inclusion of a comparison group; outcomes included validated measures of depression (primary) and social connection/loneliness (secondary). Excluded: qualitative studies, reviews, editorials, commentaries, book chapters, clinical patient samples, and interventions exclusively using psychological therapies (e.g., CBT, mindfulness, ACT) without an explicit social connection focus. Screening/selection: Titles/abstracts screened (one reviewer), full-text assessment (primary reviewer with 10% double-screened; 100% agreement). Reference lists checked; corresponding authors contacted for additional eligible studies. Data extraction: Conducted independently by two authors using a piloted Excel form; extracted study characteristics, population descriptors, intervention details (mode, duration, dosage), measures, findings, and funding; discrepancies resolved by a third author. Risk of bias: RCTs assessed with Cochrane RoB 2.0; non-randomised studies with ROBINS-I; dual independent assessment with consensus resolution. Synthesis and analysis: Narrative synthesis with subgrouping by delivery modality (in-person vs online) and sample type (higher education students vs others). Random-effects meta-analyses using standardised mean differences (SMD) for depression and loneliness; heterogeneity assessed with I²; funnel plots visually inspected (Egger’s not used due to <10 studies). Subgroup effects presented by modality/sample; sensitivity analyses excluded studies with serious risk of bias.

- Study yield: 6 studies included (3 RCTs; 3 non-randomised), conducted in USA (3), Canada, Australia, South Korea; samples largely higher education students (5 studies); one study with youth involved in street life. - Interventions: 4 group-based, 1 app-based (individual), 1 single-session reading/reflection (individual); durations from single session to 10 weeks. - Risk of bias: RCTs mostly had some concerns; non-RCTs ranged from moderate to serious risk due to confounding, deviations, missing data, and measurement biases. - Depression (all included studies): Overall reduction associated with interventions (SMD = -0.22; 95% CI -0.35 to -0.08; p=0.002; I²=0.0%). - Depression (sensitivity excluding serious risk of bias studies): SMD = -0.19; 95% CI -0.33 to -0.05; p=0.008; I²=0.0%. - Subgroups for depression: • In-person interventions with higher education students: SMD = -0.19; 95% CI -0.34 to -0.03; p=0.020. • Online app (Nod): SMD = -0.27; 95% CI -0.54 to -0.00; p=0.048. • Youth involved in street life: SMD = -0.64; 95% CI -1.71 to 0.42; p=0.235 (not significant). - Loneliness (pooled, 3 studies): No significant overall effect (SMD = -0.10; 95% CI -0.24 to 0.05; p=0.188; I²=0.0%). - Social connection outcomes: Generally beneficial effects across diverse measures (belongingness, social functioning, interpersonal relationships, social support), though the Nod app showed no overall effect on social connection indices despite interaction effects benefiting students with higher baseline loneliness/depression. - Notably absent: No study tested whether changes in social connection/loneliness mediated improvements in depression.

Findings indicate that social connection interventions for non-clinical young adults can yield small but meaningful reductions in depressive symptoms, with negligible statistical heterogeneity. While pooled effects on loneliness were not significant, several individual studies improved social connection-related outcomes, suggesting interventions can enhance aspects of social connectedness even if loneliness reductions are not uniformly detected across measures/timepoints. Engagement appears critical: the app-based intervention showed limited overall social connection effects amid low challenge completion, hinting that facilitated, group-based formats may outperform self-directed approaches for social connection outcomes. Differential benefits emerged for subgroups: greater effects were observed among students with higher baseline loneliness/depression, those from lower socioeconomic backgrounds, transfer students, and some racially minoritized groups (e.g., Black students in a social belonging intervention). These patterns suggest targeted prevention strategies may boost impact. However, evidence is largely confined to higher education settings in high-income contexts, with limited generalizability to non-student or higher-risk populations (e.g., street-involved youth), where engagement barriers and broader social determinants complicate effects on depression. Importantly, no included study examined whether improvements in social connection/loneliness mediated depression reductions, leaving mechanisms of change untested.

Social connection interventions show promise for reducing depressive symptoms and improving some social connection outcomes among young adults, particularly in higher education settings, with small overall effects. Evidence remains limited in scope and quality. Future research should recruit larger, more diverse samples beyond universities (including workplaces and NEET populations), employ longer follow-up, compare online, in-person, self-directed, and group-based formats, target groups at elevated social or mental health risk, and test mechanisms (e.g., whether enhancing social connection/loneliness mediates depression changes).

- Small number of eligible studies and predominance of higher education samples from high-income settings limit generalizability. - Risk of bias concerns across studies (some concerns to serious), including confounding, deviations from intended interventions, missing data, outcome measurement, and inability to blind participants. - Heterogeneity of social connection measures precluded pooled analyses for most social outcomes; loneliness pooled analyses included only three studies. - Grey literature and qualitative studies were excluded, potentially introducing publication bias and limiting insights into acceptability and implementation processes. - Low engagement in the app-based intervention may have attenuated effects; mechanisms linking social connection changes to depression were not tested.