Blood Test May Predict Dementia Risk Decades Before Symptoms Emerge
Scientists in the United States have identified a blood-based protein marker capable of indicating a woman’s likelihood of developing dementia up to 25 years before any cognitive symptoms become apparent, according to research published in the journal JAMA Network Open in March 2026.
The study, conducted by researchers at the University of California San Diego, centred on a protein known as phosphorylated tau 217 — commonly referred to as p-tau217 — which reflects early biological changes in the brain associated with Alzheimer’s disease. Crucially, elevated levels of this protein were detectable in blood samples taken from women who were cognitively healthy at the time, suggesting the marker may serve as a very early warning signal long before memory difficulties emerge.
The research drew on data from 2,766 women aged between 65 and 79, all of whom were enrolled in the Women’s Health Initiative Memory Study during the late 1990s. Participants were tracked for up to 25 years, and blood samples collected at the outset of the study were later analysed for p-tau217 levels. Over the course of the follow-up period, researchers identified which participants went on to develop mild cognitive impairment or dementia, and cross-referenced these outcomes against their initial biomarker readings.
The findings showed a clear pattern: women with higher concentrations of p-tau217 in their blood at the start of the study were significantly more likely to develop dementia in later life, with the greatest risk observed in those with the highest recorded levels.
However, researchers also found that the predictive strength of the biomarker varied between different groups. Women over the age of 70 at the time of enrolment showed a stronger association between elevated p-tau217 and subsequent cognitive decline than their younger counterparts.
The link was also more pronounced among women carrying the APOE ε4 gene variant — a known genetic risk factor for Alzheimer’s disease — and among those who had received combined oestrogen and progestin hormone therapy. The study further noted differences between white and Black participants, though combining the biomarker with age improved predictive accuracy across both groups.
For care home operators and nursing staff, the implications of this research are significant. With an ageing residential population, any advance that could allow earlier identification of individuals at heightened dementia risk offers the potential for more proactive care planning, lifestyle interventions, and family discussions to take place well ahead of a formal diagnosis.
A key practical advantage highlighted by the researchers is that blood-based testing is far less invasive than existing methods such as brain imaging or lumbar puncture to collect cerebrospinal fluid — procedures that are costly, uncomfortable, and not readily available in community or residential care settings. A straightforward blood test could, in principle, be incorporated into routine clinical assessment, though the researchers are clear that considerably more work is needed before that becomes a reality.
At present, blood biomarker testing of this kind is not recommended for use in people who show no symptoms of cognitive impairment. The research team stressed that further studies are required to establish how p-tau217 measurement might be integrated into clinical practice, and whether acting on early identification genuinely improves long-term outcomes for patients.
Future investigations will also examine how factors including hormone therapy, genetics, and age-related health conditions interact with p-tau217 levels throughout a person’s lifetime, potentially refining the picture of who is most at risk and when intervention would be most effective.
Michelle Dyson CB, Chief Executive Officer at Alzheimer’s Society, said: ‘Blood tests could transform how dementia is diagnosed and research we’re funding aims to make a blood test routinely available on the NHS for symptomatic Alzheimer’s disease within the next few years.
‘This study suggests that there may be a correlation for women between having a higher level of the p-tau127 biomarker earlier in life with an increased risk of developing dementia 25 years later.
These findings are promising, but of course more research is needed to understand whether early identification of biomarkers can affect whether people will go on to develop dementia later on.”
