A simple blood test may predict dementia risk decades before symptoms

A new study finds a blood biomarker, p-tau217, can signal dementia risk up to 25 years early, offering a crucial window for early detection, monitoring, and preventive interventions

What if a simple blood test could tell you, decades in advance, whether you might develop dementia? According to a new study, this might be possible. 

The study titled Plasma Phosphorylated Tau 217 and Incident Mild Cognitive Impairment and Dementia in Older Women, published in JAMA Network Open, shows that researchers have found that a protein in the blood, called p-tau217, may predict dementia risk up to 25 years before symptoms appear, offering a vital window for early intervention and prevention. 

The biomarker phosphorylated tau 217 (p-tau217) is linked to early brain changes seen in Alzheimer’s disease. According to researchers, tau proteins help stabilise brain cells, but when they become abnormally phosphorylated, they form tangles that disrupt brain function. The study authors say that p-tau217 reflects this early damage, long before memory problems begin.

 

Can a blood test predict dementia decades in advance?

Scientists at the University of California, San Diego, followed 2,766 cognitively healthy older women for up to 25 years. They found that women with higher levels of p-tau217 at baseline were significantly more likely to develop mild cognitive impairment (MCI) and dementia. 

In fact, the biomarker signal appeared up to 25 years before diagnosis, suggesting that dementia-related changes may begin decades earlier. 

According to the study authors, each increase in p-tau217 levels was linked to a 2.4 times higher risk of MCI or dementia. 

Women in the highest quartile of p-tau217 levels had the greatest risk, with some analyses showing up to a 7-fold increase in dementia risk compared to those with the lowest levels. The study found stronger associations in:

• Women aged over 70 years
• Those carrying the APOE ε4 gene variant (a known Alzheimer’s risk factor)
• Women receiving oestrogen plus progestin hormone therapy

READ | How starting exercise in your 40s can reduce dementia risk by nearly half 

Why is this biomarker important for early dementia detection?

Currently, diagnosing Alzheimer’s disease often relies on brain imaging (PET scans) and spinal fluid analysis. These methods are expensive, invasive, and not widely accessible. 

In contrast, blood-based biomarkers like p-tau217 are simpler, cheaper, and scalable, making them a promising tool for large-scale screening and research.

Can this blood test be used clinically right now?

The researchers say that while the findings are promising, blood-based biomarkers are not currently recommended for routine clinical use in people without symptoms. They call for more studies to test the results in real-world settings.  READ: Poor sleep may age your brain faster, scientists find in major study

What does early detection mean for dementia prevention strategies?

The study authors say that if dementia risk can be identified decades earlier, it opens the door to:

• Lifestyle interventions (diet, exercise, brain health)
• Closer monitoring of at-risk individuals
• Development of preventive therapies

The goal is ultimately to delay or even prevent dementia, not just detect it early, say the researchers in the study.