Alzheimer’s Brain Changes Widespread with Age, Blood Test Reveals
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A groundbreaking new study published in Nature reveals that Alzheimer’s-related brain changes are far more common with age then previously understood, offering both hope and complexity for the future of early detection through blood-based screening.
Dementia, with Alzheimer’s disease (AD) as its leading cause, remains a major global health crisis. For years, definitively diagnosing these changes required invasive and impractical methods like cerebrospinal fluid analysis or positron emission tomography. Now, researchers are making strides with blood-based biomarkers, specifically focusing on a marker called plasma phosphorylated tau at threonine 217 (pTau217).
The study, conducted by an international team of researchers, estimated the prevalence of Alzheimer’s disease neuropathological changes (ADNCs) in adults aged 70 and older. Investigators analyzed 11,486 plasma samples from the Trøndelag Health (HUNT) population studies in Norway, encompassing participants from two cohorts: HUNT3 (ages 58-69.9) and HUNT4 70+ (ages 70 and older). formal cognitive assessments were performed on the HUNT4 70+ cohort, classifying participants as cognitively normal, having mild cognitive impairment (MCI), or dementia.
“These findings underscore the importance of understanding the full spectrum of Alzheimer’s pathology, even before symptoms manifest,” stated a senior researcher involved in the study.
Age as a Primary Driver of Alzheimer’s Pathology
The research demonstrated a marked increase in ADNC prevalence with age.Among adults aged 58-69.9 years, less than 8 percent exhibited ADNC positivity, defined by a pTau217 concentration of 0.63 pg/mL or higher. However, this figure climbed dramatically, approaching 65 percent in individuals over 90 years old.
Interestingly, the study also investigated the association between ADNC positivity and various health conditions. While factors like cardiovascular disease and diabetes were linked to increased ADNC prevalence, conditions such as cancer, and chronic obstructive pulmonary disease did not demonstrate a meaningful association with ADNC positivity after adjusting for other factors.
Implications for Early Detection and Treatment
These findings have significant implications for the future of Alzheimer’s disease management. Based on current eligibility criteria, approximately 10-11 percent of individuals aged 70 and older may qualify for emerging anti-amyloid disease-modifying therapies. However, predictive value analyses revealed that the positive predictive value of the pTau217 biomarker increases with age, while the negative predictive value declines. This highlights the need for careful interpretation of results, notably in younger individuals.
“while a positive blood test doesn’t automatically equate to a diagnosis, it provides valuable information for risk assessment and potential intervention,” explained one analyst following the study’s release.
The researchers emphasize that the results should be interpreted at a population level rather than as definitive individual diagnoses, given that the classification relied on a blood-based surrogate marker. Further research is crucial to refine the interpretation of intermediate biomarker results and to develop effective follow-up strategies..
Ultimately, this study underscores the urgent need for continued investment in Alzheimer’s research and the development of accessible, accurate, and affordable diagnostic tools. The widespread prevalence of adncs,even in the absence of symptoms,suggests that early detection and intervention may be key to slowing the progression of this devastating disease.
Journal reference: Aarsland,D., Sunde, A.L.,Tovar-Rios,D. A., Leuzy, A., Fladby, T., Zetterberg, H., Blennow, K., Tan, K., De Santis, G., Yakoub, Y., Arslan, B.,Huber,H., Pola, I., Grötschel, L., Di Molfetta, G., Skjellegrind, H. K.,Selbaek,G., and Ashton, N. J. (2025). Prevalence of Alzheimer’s disease pathology in the community. Nature. DOI: 10.1038/s41586-025-09841-y, https://www.nature.com/articles/s41586-025-09841-y
