Estimating the prevalence of amyloid positivity among older adults without dementia in the general population

Abnormal brain accumulation of amyloid-β peptides, represents one of the earliest biological indicators of Alzheimer’s disease (AD) risk. Estimation on amyloid positivity (A + ) prevalence among older adults without dementia are needed to assess the epidemiological impact of AD diagnosis solely through biological markers. We combined data from the French MEMENTO clinical cohort, where amyloid status was assessed through reference procedures, with the nationally representative SHARE-HCAP survey. Using stabilized inverse odds of selection weights, we adjusted the MEMENTO sample to estimate the prevalence of A+ in the French population aged 65–85 without dementia and their five-year risk of developing AD dementia. A + prevalence was 21.4% (95% CI: 18.4–24.7) in French adults aged 65–85 without dementia i.e. approximately 2.5 million individuals, reaching 27.5% in the 80–85 age group. Over five years of follow-up, the cumulative incidence of AD dementia was 22.7% among A+ individuals, 8.0% among cognitively normal A + adults and 62.3% among those with mild cognitive impairment. While A + is common in older adults without dementia, most do not develop dementia within five years. Defining AD by A + could substantially increase diagnoses, raising major public health, ethical, and health system challenges, especially as new anti-amyloid therapies emerge.