The potential for dementia prevention in Japan: a population attributable fraction calculation for 14 modifiable risk factors and estimates of the impact of risk factor reductions

Background: As dementia prevalence increases globally, preventive strategies targeting modifiable risk factors have become increasingly important. In Japan, with its super-ageing society, dementia is the leading cause of increased disability-adjusted life years among older adults. This study quantified the contribution of 14 potentially modifiable risk factors for dementia in older adults using Japan-specific prevalence data. Methods: Commission report on dementia. We then modelled how 10% and 20% reductions in each risk factor would affect national dementia prevalence. Findings: The weighted combined PAF for all 14 risk factors was 38.9%, indicating that nearly 4 in 10 dementia cases in Japan might be preventable. Hearing loss (6.7%), physical inactivity (6.0%), and high LDL cholesterol (4.5%) were the largest contributors. Reducing all risk factors by 10% could prevent ∼208,000 dementia cases; reducing them by 20% could prevent ∼407,000 cases. Interpretation: Dementia preventive efforts in Japan should prioritise hearing care, physical activity, and metabolic health. Japan-specific data confirmed that hearing loss is a leading contributor to dementia, underscoring the urgency to increase public awareness and access to hearing interventions. Funding: The Royal Danish Embassy in Japan, Danish Ministry of Foreign Affairs, Danish Ministry of Health, and Japan Agency for Medical Research and Development funded this study.