FinnDiane LifeOne Study: influence of ageing on people with type 1 diabetes - a prospective observational cohort study protocol.

introductionLife expectancy for people with type 1 diabetes has increased due to improved treatment of diabetes and its comorbidities, allowing many to reach old age. Still, we lack knowledge of how individuals with type 1 diabetes age. On one hand, those who reach older age can be considered survivors, but on the other hand their long-standing diabetes might still exhibit negative impacts on their health and functional ability. Healthy ageing is the WHO's priority for this decade. The focus has shifted from chronological age to functional ability, which reflects the ability of individuals to perform meaningful activities. Functional ability is shaped by intrinsic capacity, the environment and their interaction. Intrinsic capacity encompasses five main domains: cognition, vitality, sensory function, locomotion and psychological domain. This observational study aims to assess how this vulnerable group of individuals with type 1 diabetes age and to identify factors that contribute to their healthy ageing, intrinsic capacity and its domains. METHODS AND ANALYSIS: The FinnDiane LifeOne Study is a prospective observational cohort study. We aim to recruit a minimum of 300 individuals with type 1 diabetes from the FinnDiane Study, aged >65 and a minimum of 100 matched controls without insulin-dependent diabetes. The cohort will be comprehensively characterised, including clinical assessment, laboratory tests, questionnaires and a geriatric assessment of different aspects of functioning ability, with 5 years intervals. We will compare the individuals with type 1 diabetes to their matched controls. For those with type 1 diabetes, we will further assess which factors from the FinnDiane baseline and trajectories during follow-up predict healthy ageing in above 65-year-olds. ETHICS AND DISSEMINATION: The LifeOne Study protocol is approved by the Ethics Committee of HUS Helsinki University Hospital (HUS/4387/2023) and the study adheres to the Declaration of Helsinki. Written informed consent is obtained from each participant. Findings will be published in international peer-reviewed journals with an open access choice. TRIAL REGISTRATION NUMBER: NCT07289204.