Relationships between alcohol use and dementia: protocol for an observational study in the UK Clinical Practice Research Datalink.

INTRODUCTION: Alcohol consumption is an increasingly recognised modifiable risk factor for dementia, yet whether it has differential impacts on dementia subtypes and its role in disease progression remains unclear. This study aims to: (1) quantify the association between alcohol intake and incidence of dementia subtypes and (2) examine whether individuals who drink heavily and develop dementia referred to hereafter as 'alcohol-related'-have poorer post-diagnosis outcomes compared with other dementia cases. Clarifying these relationships will determine whether alcohol selectively increases risk for specific dementia phenotypes or broadly heightens neurodegenerative vulnerability, with implications for prevention, clinical counselling and therapeutic targeting. METHODS AND ANALYSIS: This population-based cohort study of alcohol and dementia will use linked UK electronic health records from Clinical Practice Research Datalink, Hospital Episode Statistics and Office for National Statistics (ONS). Participants will be eligible if they have available linked data from January 1998, when ONS death registrations became available, until the end of follow-up. Alcohol exposure will be defined through self-reported recorded weekly alcohol units and diagnostic codes for harmful or dependent alcohol use. Primary outcomes including incident all-cause and subtype-specific dementia (eg, Alzheimer's, vascular, Lewy body, Parkinson's, frontotemporal) as well as secondary outcomes (ie, mortality, care-home entry and neuropsychiatric symptoms). Key covariates encompassing socio-demographic factors, smoking and relevant comorbidities will be adjusted for. Multivariable Cox proportional hazards and Fine-Gray competing risk models will estimate associations with dementia incidence. Post-diagnosis prognosis will be compared for dementia in individuals with a history of heavy alcohol use ('alcohol-related') and dementia in individuals with minimal alcohol exposure ('non-alcohol-related') cases using survival and logistic regression models. Multiple testing correction will be applied across dementia subtype comparisons. Alcohol exposure will be modelled continuously and non-linearly using restricted cubic splines and categorically using binary indicators of harmful/dependent use. Missing covariate data will be assessed and addressed using appropriate methods, including multiple imputation and complete-case analysis. Data extraction and analysis are scheduled from October 2025 to October 2026. ETHICS AND DISSEMINATION: Use of de-identified routine data will proceed under existing Research Ethics Committee and data governance approvals. Findings will be disseminated via open-access peer-reviewed journals, academic conferences and summaries targeted at patient, public and policy audiences. The results of this study will be reported according to the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) and The REporting of studies Conducted using Observational Routinely-collected health Data (RECORD) guidelines.