SummaryBackgroundQuantifying the proportion of dementia attributable to highly prevalent modifiable risk factors, such as hypertension, is important in informing effective dementia prevention strategies. We aim to quantify the population attributable fraction (PAF) of hypertension for dementia (the proportion of dementia cases that would not occur if hypertension was eliminated) at global, regional, and national levels.MethodsIn this study, we searched international and governmental websites for global, regional, and national data reporting population hypertension (according to 10-year age categories) and dementia prevalence. MEDLINE was searched for studies reporting the risk of dementia from age at hypertension diagnosis from database inception to December 31, 2022. Longitudinal observational studies with >500 participants reporting hazard ratios by age at hypertension diagnosis for risk of future all-cause dementia were eligible for inclusion. Studies excluded had cross-sectional methodology, specific vascular dementia or ‘cognitive impairment’ outcomes, and no age-specific metrics of association reported. The PAF of hypertension for dementia was calculated globally and for each country and region worldwide.FindingsData from the Global Burden of Disease, United Nations Population Prospectus, NCD Risk Factor Collaboration, UK Biobank, and Atherosclerosis Risk in Communities Study were obtained. 186 countries reported dementia and hypertension prevalence data. The global PAF of hypertension for dementia was 15.8% [95% Credible Interval (CI), 8.8%–22.7%]. Latin America and the Caribbean (18.0% [95% CI, 9.4%–26.6%]), and Europe (17.2% [95% CI, 9.6%–24.7%]) had the highest PAF of hypertension for dementia. Hypertension diagnosed between the ages of 30–44 had the highest age-specific global attributable fraction for dementia (8.4% [95% CI, 3.4%–13.5%]), followed by ages 45–54 (2.92% [ 95% CI, 0.96%–4.88%]), 55–64 (2.59% [95% CI, 1.15%–4.03%]) and 65–74 (1.82% [95% CI, −2.31%–5.96%]).InterpretationThe population attributable risk of hypertension for dementia is 15.8%, suggesting that optimal detection and treatment, particularly at midlife, has the potential to markedly reduce the global burden of dementia.Funding10.13039/100010269Wellcome Trust;Health Research Board of Ireland;10.13039/100000957Alzheimer's Association.