OP100 Hypertension and risk of dementia and its subtypes: evidence from a prospective cohort of 1.3 million women

Background Hypertension in midlife has been associated with an increased risk of all-cause dementia, but the evidence is unclear on the strength of the association and short-term studies may be affected by reverse causation bias. The observational evidence points to an association between hypertension and vascular dementia, but most previous studies have lacked statistical power. The evidence for an association between hypertension and Alzheimer’s disease is inconsistent. We aimed to examine these associations in a large study of UK women, with a mean of 19 years of follow-up. Methods The Million Women Study is a population-based prospective cohort study of 1.3 million women aged 50–64 invited for NHS breast cancer screening in median year 1998 (IQR 1997–1999). After excluding participants with a record of dementia at recruitment, participants who provided data on current treatment for hypertension were followed-up to the end of 2019 through electronic linkage to NHS records of hospital admissions with mention of dementia. Taking medication for hypertension was a proxy measure for having clinically-relevant elevated blood pressure. We used Cox regression to assess dementia hazard ratios (HRs) and 95% confidence intervals (CIs) in relation to hypertension, with time in study as the underlying time variable, stratified by year of birth, year of recruitment and region, and adjusted for deprivation, education, smoking, alcohol, menopausal hormone therapy, physical activity, body mass index, diabetes and high cholesterol at recruitment. We excluded the first 15 years of follow-up to minimise any reverse causation bias. Results 16% (219,324/1,363,471) of women at recruitment reported current treatment for hypertension. During the period of follow-up ≥15 years from recruitment, there were 45,690 cases of dementia among the 1,202,410 women included in the analysis. Self-reported current treatment for hypertension was associated with an increased risk of all-cause dementia (HR 1.19, 95% CI 1.17–1.22). Analyses by subtype showed that current treatment for hypertension was associated with vascular dementia (HR 1.50, 95% CI 1.43–1.58) but not with Alzheimer’s disease (HR 1.04, 95% CI 0.99–1.08). 44% of those reporting current treatment for hypertension in midlife also reported having had hypertension during pregnancy and therefore analyses are planned to assess if a history of hypertension in pregnancy confers any additional risk. Conclusion These results confirm the hypothesis that hypertension during midlife is a risk factor for all-cause dementia, and provide evidence for an association with vascular dementia but not for an association with Alzheimer’s disease.