Study protocol: Longitudinal observational study on frailty and mental health

Introduction: Frailty is a dynamic condition associated with increased vulnerability to adverse health outcomes in older adults. While previous research has primarily focused on deficit-based mental health factors, such as depression and loneliness, less is known about the role of positive mental health determinants, including well-being, resilience and social connectedness, in the development and progression of frailty. Understanding both risk and protective factors is essential for informing public health strategies aimed at promoting healthy ageing. This study aims to examine the longitudinal relationship between mental health and frailty in a nationally sampled population of adults aged 50 years and older in Slovenia. Methods and analysis: This longitudinal observational study will collect data at four time points over a two-year period (January 2026-March 2028). A stratified random sample of community-dwelling adults aged 50-84 years will be drawn from the national population registry, with 5,000 individuals invited to participate in the first wave. Frailty, mental health and a set of social, psychological, and health-related factors will be assessed. Data will be analyzed using a combination of descriptive, inferential and longitudinal statistical methods to examine associations between frailty and mental health over time. Potential explanatory factors will also be explored within the longitudinal framework, and additional analyses will assess the impact of attrition. Ethics and dissemination: The study has been approved by the Ethics and Deontology Committee of the National Institute of Public Health. Participation is voluntary, and informed consent will be obtained from all participants. Data will be anonymized and handled in accordance with applicable data protection regulations. Findings will be disseminated through peer-reviewed publications, conference presentations and public health reports to inform strategies for promoting healthy ageing.