Longitudinal physical-mental multimorbidity trajectories by sociodemographic factors: a cohort study using electronic health records in Scotland (2000-2021).

Multimorbidity, the co-occurrence of two or more chronic conditions, is a pressing global health challenge. However, research capturing the dynamic, longitudinal nature of health trajectories, particularly the intersection of physical and mental domains, remains scarce compared to traditional cross-sectional "snapshots." Leveraging up to 21 years of electronic health records data from 858,789 Scottish patients in the University of Dundee Health Informatics Centre, we used multistate modelling to explore how individuals transition from a disease-free baseline into multimorbidity, evaluating how age, sex, and socioeconomic status shape these pathways. Overall transition estimates were driven by the younger demographic of our baseline disease-free cohort. The findings highlight the critical role of severe, hospital-contacting mental health conditions in driving early-onset multimorbidity, particularly in young men and socioeconomically disadvantaged groups. These findings underscore the urgent need to prioritise integrated physical-mental care and address upstream structural determinants of health. This temporal approach identifies high-risk populations for targeted early interventions and informs policy initiatives aimed at reducing health disparities.