Effectiveness of a nature-based social prescribing intervention on loneliness and health-related quality of life among vulnerable urban adults (RECETAS-BCN): an observer-blinded randomised controlled trial.

Background: Loneliness is a major public health problem disproportionately affecting vulnerable populations and has well-recognised health consequences. The RECETAS-BCN study tests the effectiveness of 'Friends in Nature (FiN)', a facilitator-led group and nature-based social prescribing (NBSP) intervention, built on existing evidence, to reduce loneliness and improve health-related quality of life (HRQoL) among adults. Methods: In this observer-blinded, parallel randomised controlled trial, we recruited lonely adults (18+), from 12 neighbourhoods with low socioeconomic levels in the Barcelona metropolitan region of Spain. Participants were randomised (1:1) into two NBSP pathways: 1) group-based sessions 1x/week for nine weeks (intervention arm, n = 160), and 2) active signposting (active-control arm, n = 160). Co-primary outcomes were loneliness (De Jong Gierveld Loneliness Scale = DJGLS) and HRQoL (15D). Outcomes were assessed at M0, M3 (primary endpoint), M6, and M12. Trial registration #NCT05488496 at ClinicalTrials.gov. Findings: Between January 10, 2023, and June 11, 2024, 320 (78%) of 411 screened adults (80% female; median age 62.8 years) were randomised. Early dropouts were lower in the intervention arm compared to the active-control arm (14% versus 28%, p = 0.002). One participant in the intervention arm had an adverse event. No significant changes were observed in HRQoL. At M3, both groups showed significant loneliness reductions by 10.5 percent (overall mean change: -0.73; 95% CI -1.04 to -0.42), but no significant between-group difference was observed (0.30; 95% CI -0.26 to 0.86; p = 0.296). Moderation analyses revealed a significant interaction for the baseline composite emotional wellbeing score (CSEW, p = 0.003), indicating that the FiN intervention was significantly more effective than signposting for participants with higher baseline loneliness and lower CSEW. Interpretation: Results suggest that both NBSP pathways alleviated loneliness but did not change HRQoL. These reductions in loneliness continued to increase through one year of follow up. Results point to the promising benefits of NBSP interventions for reducing loneliness in cities. Funding: European Commission H2020 programme.