Scientists have found that a simple blood test may help predict the risk of developing dementia in women long before the first symptoms appear.

A study published in JAMA Network Open showed that a specific biomarker in the blood can indicate an increased likelihood of cognitive decline and dementia about 25 years before the disease begins to manifest.

At the center of the study is a protein called p-tau217, a form of the tau protein associated with pathological processes in the brain in Alzheimer’s disease. It is known that abnormal protein structures gradually accumulate in the brain as the disease develops, but these changes can begin many years before noticeable problems with memory and thinking appear.

The research was conducted by scientists from the University of California, San Diego, who analyzed data from the long-term Women’s Health Initiative Memory Study.

The study included 2,766 women aged 65 to 79 who showed no signs of cognitive impairment at the start of the observation period. Participants were followed for approximately 25 years.

Blood samples taken at the beginning of the study were later analyzed for p-tau217 levels. The results showed that women with higher levels of this protein were significantly more likely in later years to develop memory decline, mild cognitive impairment, or dementia. The risk increased as the biomarker concentration rose.

Researchers also found that the relationship between this indicator and future cognitive problems was particularly strong in women over 70 and in carriers of the APOE ε4, which has long been considered one of the key genetic risk factors for Alzheimer’s disease.

According to the authors, such a blood test could become an important tool for early identification of people at increased risk of dementia. Unlike expensive diagnostic methods — such as brain scans or analysis of cerebrospinal fluid — a blood-based test could potentially be simpler and more accessible.

However, experts emphasize that these tests are currently used mainly in scientific research, and additional studies will be required before they can be widely implemented in routine medical practice.