Temporal comorbidity patterns in Alzheimer's disease and vascular dementia: A population‐based observational study in UK Biobank

Introduction: In Alzheimer's disease (AD) and vascular dementia (VaD), comorbidities shape disease trajectories and care needs, yet their timing across the lifespan remains poorly understood. Methods: We analyzed comorbidities using in-patient hospital International Classification of Diseases 10th Revision codes in 10,730 UK Biobank participants with AD or VaD, spanning 20 years before to 10 years after diagnosis. Logistic regression and Bayesian network analysis identified time- and subtype-specific risk patterns, validated against controls. Results: Distinct comorbidities emerged decades before diagnosis. In AD, depressive episodes, osteoporosis, and type 1 diabetes appeared up to 20 years pre-diagnosis, while VaD was characterized by early cerebral infarctions, type 1 diabetes, intestinal disorders, and rheumatoid arthritis, absent in controls. Discussion: Although restricted to severe populations captured in in-patient data, excluding primary care, these findings reveal time-dependent prodromal patterns in AD and VaD, highlighting opportunities for targeted screening, prevention, and early intervention.