A single blood protein measured in healthy older women predicted who would go on to develop dementia as much as 25 years later. Researchers at the University of California San Diego, reporting March 10, 2026 in JAMA Network Open, found that higher baseline levels of phosphorylated tau 217, or p-tau217, were strongly linked to later mild cognitive impairment and dementia among women who showed no memory or thinking problems when their blood was drawn.
The analysis drew on 2,766 participants in the Women's Health Initiative Memory Study, a national cohort that enrolled women aged 65 to 79 in the late 1990s and tracked them for up to 25 years. Every woman was cognitively unimpaired at enrollment. Their stored blood samples were analyzed years afterward for p-tau217, a form of tau that reflects the early brain changes associated with Alzheimer's disease.
The practical importance lies in the lead time. Aladdin H. Shadyab, the study's first author and an associate professor of public health and medicine at UC San Diego's Herbert Wertheim School of Public Health and Human Longevity Science and School of Medicine, said the results suggest women at elevated risk could be identified decades before symptoms emerge, opening the door to earlier prevention efforts and closer monitoring instead of waiting until memory problems disrupt daily life.
Because the cohort consisted entirely of women aged 65 and older at enrollment, the findings speak most directly to that group, and a blood biomarker that flags risk is not the same as a test that tells any individual woman she will develop dementia. Still, the long follow-up gives researchers an unusually clear window into how early these biological signals appear relative to the disease itself.