A Nature analysis of a major Norwegian study challenges existing estimates of Alzheimer’s prevalence, finding that 25% of people aged 85–89 have dementia with Alzheimer’s pathology — far higher than previous 7–13% estimates — while preclinical Alzheimer’s in younger seniors (70−74) occurs at only 8% versus earlier 22% estimates. Using blood biomarker pTau217 in 11,486 participants, researchers identified that 10% of over-70s had dementia, 10% had mild cognitive impairment, and 10% had preclinical Alzheimer’s, but warn that blood tests alone are insufficient for widespread screening due to potential harm from false positives. The discrepancies highlight how previous studies may have been skewed by selection bias, while demonstrating that blood-based biomarkers require careful interpretation and comprehensive clinical assessment.
A survey of Alzheimer’s disease prevalence in Norway confirms earlier estimates and might show how education level relates to risk.






