One blood protein, and memory changes years later

What was found

Researchers pooled six long-running studies from North America, Japan and Australia: 2,684 older adults whose memory and thinking were normal when a blood sample was taken. Over a median of about five years, 478 of them went on to develop cognitive impairment.

People with higher levels of a blood protein called p-tau217 at the start were more likely to be among them. Each step up in p-tau217 (one standard deviation) went with about a 38% higher rate of progression, and that held even after taking brain amyloid scans into account. Over five years, about 24% of the "high" group and about 38% of the "very high" group progressed. Higher levels also went with a slightly faster decline on memory and thinking tests.

Why it matters

p-tau217 is the blood protein most closely tied to the brain changes of Alzheimer's disease. Until now, most work asked whether it reflects those changes today. This study asks a different question: what a single reading means for the years ahead, in people who feel fine. That is the question clinics and their patients usually ask.

How sure we are

Fairly sure of the overall pattern: it is a large, peer-reviewed study in JAMA, and the link held across cohorts. Less sure of the long-range numbers: follow-up data thin out after about five years, and the authors say longer estimates are uncertain. The cohorts were selected research volunteers, so results may differ in the general population. The authors say the findings do not yet support routine screening of people without symptoms, and each person's risk depends on much more than one protein.