Blood Test Predicts Dementia in Women 25 Years Before Symptoms Begin
Posted on 13 Mar 2026
Dementia and Alzheimer’s disease often develop silently over many years before symptoms appear. Detecting risk earlier could allow preventive strategies to begin long before memory problems interfere with daily life. Researchers have now identified a blood-based biomarker that may predict dementia risk decades before symptoms emerge.
In a new study, scientists at the University of California San Diego (San Diego, CA, USA) focused on phosphorylated tau 217 (p-tau217), a protein associated with early brain changes linked to Alzheimer’s disease. Blood levels of this biomarker were evaluated as a predictor of long-term cognitive decline. The analysis included 2,766 participants from the Women’s Health Initiative Memory Study, which enrolled women aged 65 to 79 years in the late 1990s and followed them for up to 25 years. All participants were cognitively healthy at the beginning of the study.
Blood samples collected at baseline were later analyzed for levels of p-tau217. Over the follow-up period, researchers identified participants who developed mild cognitive impairment or dementia. Women with higher p-tau217 levels at the start of the study were significantly more likely to develop dementia later in life. The risk increased progressively with higher biomarker levels, with the highest concentrations associated with the greatest long-term risk.
The association between p-tau217 levels and dementia risk varied across different groups. Elevated levels were more strongly linked to cognitive decline in women over age 70, those carrying the APOE ε4 genetic risk factor for Alzheimer’s disease, and those who had received estrogen plus progestin hormone therapy during the study. Differences were also observed between white and Black participants, although combining p-tau217 measurements with age improved prediction accuracy similarly across both groups.
The findings, published in JAMA Network Open, suggest that blood-based biomarkers such as p-tau217 may provide a less invasive and more accessible alternative to brain imaging or spinal fluid testing for assessing Alzheimer’s risk. Earlier identification of individuals at higher risk could help researchers develop and evaluate prevention strategies before cognitive symptoms develop.
However, the investigators emphasize that blood biomarker testing is not yet recommended for routine clinical screening in individuals without symptoms. Further research is needed to determine how these biomarkers could be incorporated into clinical care and whether early detection can meaningfully reduce dementia risk.
“Our study suggests we may be able to identify women at elevated risk for dementia decades before symptoms emerge,” said Aladdin H. Shadyab, PhD, MPH, first author of the study. “That kind of long lead time opens the door to earlier prevention strategies and more targeted monitoring, rather than waiting until memory problems are already affecting daily life.”
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