A simple blood test might be able to flag dementia risk decades before symptoms show up. Researchers found that levels of a protein called p-tau217 in women's blood could predict mild cognitive impairment or dementia as far as 25 years in advance, according to a study published in the Journal of the American Medical Association.
The finding comes from tracking 2,766 American women ages 65 to 79 over 25 years, starting in the mid-1990s. By the end of the study in 2021, nearly half — 1,311 women — had developed either mild cognitive impairment or dementia. The women with higher p-tau217 levels at the start were significantly more likely to develop these conditions later. For context, p-tau217 has emerged as one of the most promising markers for detecting Alzheimer's disease in its early stages.
"The key takeaway is that our study suggests it may be possible to detect risk of dementia two decades in advance using a simple blood test in older women," said Aladdin H. Shadyab, the lead researcher at UC San Diego. "Our findings show that the blood biomarker p-tau217 could help identify individuals at higher risk for dementia long before symptoms begin."
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The research revealed some intriguing wrinkles. Women taking estrogen plus progestin hormone therapy showed a stronger link between p-tau217 levels and dementia risk compared to those on placebo. Women on estrogen alone showed no significant difference. The p-tau217 signal also appeared stronger in women over 70 and in those carrying the APOE ε4 gene, a genetic variant that increases Alzheimer's risk.
But here's where the story gets more complicated — and important. The study had a significant blind spot: it focused only on older women, and the racial makeup mattered. P-tau217 proved more predictive in white women than in Black women. In fact, the protein showed no association with mild cognitive impairment in Black women at all, though it did help predict dementia across both racial groups when age was factored in.
Ian McDonough, a researcher at SUNY Binghamton not involved in the study, flagged a critical concern: "Plasma biomarkers are not going to be a one-size-fits-all forecasting solution." He emphasized that researchers need to figure out which groups of older and middle-aged adults these markers actually work for — and crucially, which groups they might mislead. A low p-tau217 reading in a Black American, for example, could falsely suggest low dementia risk when the actual risk is high.
Beyond the Blood Test
A blood test is just one piece of the puzzle. Research consistently shows that physical activity, mental stimulation, and a healthy diet all play roles in reducing dementia risk. Catching early warning signs matters too.
Dr. Stephanie Nothelle, a geriatrician at Johns Hopkins, points to several red flags that tend to appear first: short-term memory loss, personality shifts, persistent trouble finding words, and difficulty with planning. That last one — what doctors call "executive functioning" — is worth paying attention to. It's your brain's ability to manage complex, multi-step tasks, like organizing a dinner party. If that suddenly feels impossible, it's worth mentioning to your doctor.
The real promise here isn't that one blood test will solve dementia prediction. It's that we're getting better at spotting risk years before symptoms arrive — which means more time to potentially slow or prevent what's coming.
