Association between exogenous hormone use and dementia: A prospective cohort study and synthetic analysis

To investigate the controversial association between exogenous hormone use (EHU) and dementia, with a focus on subtype-specific risks.

This prospective cohort study followed 273,069 women in the UK Biobank over 3,802,608 person-years, identifying 4,710 dementia cases.

Cox models assessed use of oral contraceptive (OC) and hormone replacement therapy (HRT) in relation to all-cause dementia, Alzheimer's disease (AD), vascular dementia (VaD), and frontotemporal dementia (FTD) across treatment durations. Subgroup analyses were stratified by age, ethnicity, APOE status, education, income, and reproductive factors. A systematic review was conducted to synthesize existing evidence.

In the cohort study, OC use was associated with reduced risks of all-cause dementia (HR 0.90, 95%CI 0.84-0.95), AD (HR 0.87, 95%CI 0.79-0.95), and VaD (HR 0.81, 95%CI 0.70-0.93), particularly after 4-14 years of use. HRT showed no significant association with increased dementia risk. Synthesized results largely corroborated these findings: OC use was associated with reduced risks of dementia (HR 0.90, 95%CI 0.89-0.92); and although four European studies reported a moderately increased AD risk after post-menopausal HRT use, neither cohort-based studies (HR 0.98, 95%CI 0.90-1.06) nor traditional case-control studies (OR 1.00, 95%CI 0.90-1.11) found an association between HRT and dementia.

Our combined evidence does not support an increased risk of dementia associated with OC use; similarly, no clear association was observed between HRT and increased dementia risk. Clinical decisions on EHU should be individualized, balancing overall benefits against potential risks.