Epidemiology of Severe Mental Disorders in Older Adults: A Population-Based Longitudinal Study in Aragón, Spain

Background/Objectives: Mental disorders represent a major public health challenge, particularly in ageing populations. This study aimed to analyse the incidence of mental disorders requiring hospital admission in Aragón (Spain), compare the epidemiological and clinical characteristics of adults aged ≥65 years with the overall adult population, and evaluate temporal and geographical variations in incidence. Methods: A retrospective population-based study included all incident cases of mental disorders requiring hospital admission in Aragón between 2021 and 2024. Data from the Aragón Healthcare Big Data Platform (BIGAN) were analysed using descriptive statistics, multivariable logistic regression, and Poisson regression. Results: A total of 3057 incident cases were identified. The average annual incidence was 57.12 per 100,000 inhabitants in the overall adult population and 51.70 per 100,000 among adults aged ≥65 years. Older adults were more frequently women and showed higher rates of disability, polypharmacy, mood disorders (F3), and organic mental disorders (F0), whereas schizophrenia spectrum disorders (F2) and readmissions were less frequent. Organic mental disorders (OR = 12.28), mood disorders (OR = 2.50), disability (OR = 3.50), and polypharmacy (OR = 6.88) were independently associated with older age. Incidence remained relatively stable but showed geographical variation, with higher rates among older adults concentrated in predominantly mountainous counties. Conclusions: Adults aged ≥65 years showed an average annual incidence comparable to the overall adult population but exhibited a distinct clinical and geographical profile. These findings support integrated, age-sensitive, and territorially adapted mental healthcare strategies for ageing populations.