A team of researchers at Stanford University has developed a groundbreaking blood test that can measure a person’s biological age, potentially offering a more accurate picture of how well someone is aging than their chronological age.
Published this week in Nature Medicine, the study—led by Professor Tony Wyss-Coray, director of the Phil and Penny Knight Initiative for Brain Resilience—examined blood samples from over 45,000 adults aged 40 to 70. Using data from the UK Biobank, the researchers analysed nearly 3,000 proteins in the blood that are unique to 11 organ systems, including the brain, heart, lungs, kidneys, and immune system.
The test identifies how proteins related to each organ change over time. These changes offer clues about the health and function of those organs, allowing researchers to calculate the “biological age” of each one. When compared to a person’s actual age, this measurement gives insights into whether they are aging faster or slower than expected.
“We’ve always known that people age at different rates, and this tool allows us to begin measuring that in a meaningful way,” said Wyss-Coray. “It opens up a new way of thinking about health and longevity.”
One of the study’s most striking findings is the central role the brain appears to play in predicting overall aging and disease risk. Researchers found that people whose brains appeared biologically younger than their chronological age had a 40% lower risk of death during the 15- to 17-year follow-up period. Conversely, those with “older” brains were more likely to develop Alzheimer’s disease and had significantly shorter life expectancies.
“Brain health, as it turns out, might be one of the best indicators of how well the rest of the body is aging,” Wyss-Coray said.
The research team used machine learning to build models that could determine a person’s biological age based on these organ-specific proteins. The most accurate predictors came from brain proteins, which not only reflected neurological health but also seemed to mirror aging processes in other organs.
While the test is not yet available for clinical use, researchers believe it could eventually help doctors identify people at higher risk of chronic illnesses, guide personalized treatment, and monitor the effectiveness of lifestyle changes or therapies aimed at slowing aging.
Although more research is needed, the findings underscore a growing belief in medicine: how old you are on the inside may matter more than the number on your birth certificate.
