To co-develop the Stay-At-Work (SAW) intervention, a person-centred, interdisciplinary, cross-sectoral vocational rehabilitation (VR) programme for individuals on, or at risk of, sick leave due to chronic low back pain (CLBP) and to advance methodological understanding of how evidence, qualitative insights, stakeholder input and programme theory can be systematically integrated and operationalised into concrete intervention components.

A three-stage intervention development study, guided by the Medical Research Council framework for complex interventions, involving evidence review and stakeholder consultation (previously reported); multistakeholder co-design; and prototyping in clinical settings.

The intervention was developed within a Danish public healthcare and welfare context, involving a secondary care spinal service, municipal employment services (n=3), municipal rehabilitation services (n=3) and general practice.

Stage 1: 17 individuals on long-term sick leave due to CLBP participated in interviews and focus groups. Stages 2 and 3: The co-design group included individuals living with CLBP (n=2); clinicians from a secondary care spine service (n=2) and municipal rehabilitation services (n=6); general practitioners (n=2); municipal employment service professionals (n=3) and local managers (n=3); and employer and employee representatives (n=2). Participants were purposively recruited based on their roles and experience in VR and return-to-work processes and contributed across different stages of intervention development.

The SAW intervention consists of eight structured activities, developed through multistakeholder co-design and underpinned by a programme theory with four core mechanisms: (1) strengthened interprofessional and cross-sectoral understanding and collaboration; (2) stronger alignment around functional capacity and work ability; (3) addressing psychological vulnerability through systematic screening and support; and (4) enhanced coordination of care and rehabilitation efforts across services.

Stakeholder input from the co-design group informed the intervention’s content and procedures, thereby improving alignment with local contexts and strengthening cross-sector collaboration. Some proposals were excluded due to inconsistency with clinical guidelines.

This study demonstrates how a structured, theory-informed co-development process can be used to integrate evidence, stakeholder input and programme theory into a coherent, cross-sectoral VR intervention. The approach enhanced transparency, supported alignment with real-world practice, and provides methodological insight to strengthen the reproducibility and transferability of complex interventions.

Registration number: The Region of Southern Denmark’s Research Registry (journal no. 23/44927).

Early-life exposures, such as nutritional deficiencies, stress, smoking, toxins, medications, diseases, infections and inflammation may affect multiple physiological and metabolic systems in the offspring, including hormonal regulation, bone metabolism and mineralisation, and body composition. Moreover, the effect of these early-life exposures on later health may potentially be mediated through adverse neonatal epigenetic reprogramming of bone-related genes affecting health later in life, especially skeletal development and bone density. Thus, to advance this research further, the overall aim of the project is to investigate if (a) neonatal epigenetic and genetic signature; (b) maternal risk factors during preconception and pregnancy, such as medicine use, diseases, socioeconomic status, major life events, weight, growth and lifestyle; (c) risk factors at birth, such as instrumental delivery, mode of delivery, medicine use, injuries, diseases, weight, size for gestational age, ponderal index, gestational age; and (d) childhood risk factors, such as diseases, medicine use, major life events, weight, growth and lifestyle are associated with hormonal status, lipids, bone turnover markers, bone mineral density, fat mass and lean body mass at age 18–19 years.

Population-based, nationwide, cross-sectional clinical study with potential for longitudinal reassessment. Danish women and men aged 18–19 years old will be selected at random from the Danish National Population Registry and invited if they have available neonatal dried blood spot cards. A total of 2000 individuals will be enrolled. The study combines register data, and neonatal epigenetic and genetic analyses from stored blood with clinical and survey data. Body composition will be measured using dual-energy X-ray absorptiometry. Adult blood and hair samples will be obtained to assess hormonal status, lipids and bone turnover markers. Height, weight, waist and hip circumference, and blood pressure will be measured. Questionnaires on well-being, sleep patterns, dietary and exercise habits, onset of puberty, use of cannabis, nicotine, alcohol and pain medication will be included. Information on medicine use, diseases, socioeconomic status, major life events, weight, growth and lifestyle will be obtained from the national administrative and health registers at the time of conception and during pregnancy for the parents, as well as from the participants throughout their lifetime. Health registries include the Danish Medical Birth Register, the National Patient Register, the Danish National Prescription Register, the National Child Health Register and Statistics Denmark. Multivariate regression analyses will be performed.

This nationwide study has been approved by the Regional Committees on Health Research Ethics for Southern Denmark (S-20230105). The study participants will be enrolled in the study following their informed written consent. Results will be submitted for publication. The Strengthening the Reporting of Observational Studies in Epidemiology Statement guidelines will be used for reporting.

NCT06509776.