Strengthening public health research on urban green and blue space interventions: the GIFT framework for theory development

Urban green and blue space (UGBS) interventions are increasingly promoted as strategies to improve population health and reduce health inequities. Yet the evidence needed to guide policy and practice remains difficult to interpret because evaluations often report mixed findings, with limited understanding of how and why health impacts vary. This partly reflects a lack of explicit programme theory specifying how interventions are expected to generate health outcomes, and why effects may differ across population groups and contexts. Without a robust, evidence-informed understanding of how interventions produce effects, policy and practice may rely on insufficiently tested assumptions about expected health benefits from UGBS interventions. This Viewpoint introduces the Green and blue space Intervention Framework for Theory development (GIFT), which supports the development of programme theory for UGBS intervention studies. GIFT was developed through a survey, workshop, and iterative feedback involving 25 international researchers. It provides guiding questions covering intervention components, pathways and mechanisms, population variation, contextual conditions, outcomes and timescales. By providing a shared approach to articulating how UGBS interventions are expected to work, GIFT can support more theory-informed evaluations, improve interpretation of findings, strengthen judgements about transferability, and generate more actionable evidence for effective and equitable UGBS interventions.