A blood-based biomarker known as phosphorylated tau 217 (p-tau217) may help identify older adults at high risk of developing Alzheimer’s disease years before symptoms appear, according to findings from a large multicohort study.

Researchers analyzed data from 2,684 cognitively healthy participants enrolled in six long-term aging and Alzheimer’s disease studies. The participants were followed for as long as 13.5 years to determine whether blood levels of p-tau217 could predict future cognitive decline.

The study found that individuals with elevated p-tau217 levels were significantly more likely to progress to cognitive impairment than those with lower levels. Participants whose p-tau217 concentrations exceeded 2.5 standard deviations above the average had an estimated 38% chance of developing cognitive impairment within five years, with the risk continuing to increase over the following decade.

Researchers said the findings reinforce the growing role of blood-based biomarkers in detecting Alzheimer’s disease during its earliest stages, before memory loss and other clinical symptoms become apparent.

P-tau217 is a modified form of the tau protein, one of the biological hallmarks of Alzheimer’s disease. In affected individuals, abnormal phosphorylation causes tau proteins to accumulate into toxic tangles that damage brain cells and promote chronic inflammation, contributing to progressive neurodegeneration.

The development of blood tests for Alzheimer’s risk represents a major advance over traditional diagnostic methods, which often rely on costly brain imaging or invasive cerebrospinal fluid analysis. Blood-based testing is increasingly being incorporated into observational studies and clinical trials aimed at improving early detection and evaluating preventive therapies.

Despite the promising results, researchers caution that the tests are not yet ready for widespread clinical use. While elevated p-tau217 levels can identify individuals at greater risk, there is currently no approved treatment that can reliably prevent Alzheimer’s disease in people who have not yet developed symptoms.

Health experts generally recommend that individuals identified as being at higher risk focus on evidence-based measures associated with better brain health. These include regular physical activity, a balanced diet, cardiovascular risk management, quality sleep, cognitive engagement and social interaction.

Scientists are also exploring whether reducing chronic inflammation, preventing persistent viral infections, or enhancing immune function through vaccination could help lower dementia risk. However, these approaches remain under investigation and require further clinical evidence before becoming standard recommendations.

The authors concluded that plasma p-tau217 has strong potential as a prognostic biomarker for estimating long-term risk of cognitive decline among cognitively healthy older adults. They emphasized that additional research involving more diverse and representative populations is needed to validate the findings and determine how the test can best be integrated into routine clinical care.

The study adds to growing evidence that blood-based biomarkers could play a key role in identifying individuals most likely to benefit from future preventive interventions, potentially enabling earlier action against one of the world’s leading causes of dementia.