Alzheimer’s biology can begin decades before a clinical diagnosis, but most blood-biomarker studies have focused on older adults or people already diagnosed. A Lancet study highlighted by NIH on 1 July shifts the question earlier: what do amyloid-beta and tau in blood correlate with while people are still in midlife? [1][2][3]

The cohort and the signal

Researchers used the long-running CARDIA study and analysed blood samples and cognitive tests from 1,350 participants at a follow-up examination between 2020 and 2022. None had a dementia diagnosis. The team measured three plasma markers, including forms of amyloid-beta and phosphorylated tau that are used as indicators of plaques and tangles in the brain. Depending on the marker and threshold, 4% to 15% of participants had levels high enough to suggest Alzheimer’s-related pathology. [1][2]

Those participants performed worse on processing-speed and executive-function tests. Among people who had taken similar tests five years earlier, higher biomarker levels were also associated with a greater chance of a large decline in processing speed and steeper verbal-memory decline. The association is important, but it is still an association: the cohort does not prove that the blood proteins caused the cognitive changes or that an individual with a high result will develop dementia. [1][2]

Why timing changes the research question

A blood test is easier to repeat than a brain scan or spinal-fluid test, so it could make longitudinal research more practical. It might help investigators recruit prevention trials or study when biological changes begin. That is different from declaring a screening test ready for routine use. The UCSF research group stresses that the paper studied links between plasma markers and midlife cognition, not a clinical diagnosis in symptom-free people. [3]

The useful learning bridge is physical memory architecture. Amyloid plaques, tau tangles, synapses and cognitive tests sit at different levels of the same system. A biomarker is a measurement of one layer; it becomes clinically meaningful only when validated against outcomes, reference standards and a decision that improves care. This distinction is essential because early detection can carry anxiety, cost and false-positive risks as well as potential benefits.

Readers should not use this briefing to interpret a personal result or change medical care. Any real-world test requires a qualified clinician, validated assay and context about symptoms and other conditions. The current evidence supports further research into earlier biology, not a promise about one person’s future.

Production note: This briefing was researched and drafted with AI assistance by Anayati and was not reviewed by a human.

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References

Alzheimer’s proteins in blood linked to midlife cognition

Alzheimer's disease neuropathology plasma biomarkers and cognition in midlife: a community-based cohort study

Higher levels of AD biomarkers linked to cognitive performance at midlife