Brain Age Identified as Strongest Predictor of Alzheimer's and Death
A new blood test measures biological age of organs, predicting disease and death more accurately than birth age.
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A study led by researchers at Stanford Medicine has developed a method for assessing the biological age of individual organs using protein levels in blood samples. The findings show that differences in organ-specific biological age can predict disease risk and mortality more accurately than chronological age alone.
The work, published in Nature Medicine, used data from more than 44,000 participants in the UK Biobank study to analyze blood levels of nearly 3,000 proteins, some of which are known to originate from specific organs. The analysis covered 11 major organ systems, including the brain, heart, lungs, liver and kidneys.
A new way to assess aging
While chronological age measures time since birth, biological age reflects physiological condition. Researchers applied machine learning to compare the protein signatures of individuals’ organs against population-wide averages for each age group. Each organ received a biological age score indicating whether it was aging faster or slower than average.
An organ was classified as “extremely aged” or “extremely youthful” if its biological age differed by more than 1.5 standard deviations from the age-adjusted mean. One-third of study participants had at least one organ that met this threshold, and one in four had multiple such organs.
The analysis found that accelerated aging of a specific organ strongly correlated with the development of diseases associated with that organ. For example, an aged heart was linked to higher risk of atrial fibrillation and heart failure, while aged lungs were associated with increased risk of chronic obstructive pulmonary disease.
“With this indicator, we can assess the age of an organ today and predict the odds of your getting a disease associated with that organ 10 years later.”
Dr. Tony Wyss-Coray
The brain as a key predictor
The biological age of the brain showed the strongest link to health outcomes. Participants with biologically aged brains were more than three times as likely to develop Alzheimer’s disease compared to those with normally aged brains. Conversely, biologically youthful brains were associated with a significantly reduced risk of Alzheimer’s.
Brain age also emerged as the best single predictor of overall mortality. Individuals with aged brains had an 182% higher risk of death over a 15-year period, while those with youthful brains had a 40% lower risk.
“The brain is the gatekeeper of longevity. If you’ve got an old brain, you have an increased likelihood of mortality. If you’ve got a young brain, you’re probably going to live longer.”
Dr. Tony Wyss-Coray
Implications for preventive medicine
The researchers propose that biological age profiling could become a valuable tool in preventive healthcare. By identifying organ-specific risks before symptoms arise, clinicians may be able to intervene earlier with targeted therapies or lifestyle changes.
This method may also help assess the effects of longevity interventions. Future clinical trials could use biological age as a metric to evaluate how specific drugs or behaviors influence the aging trajectory of different organs.
Although the test is not yet available for clinical use, Stanford University has licensed the technology to two companies co-founded by the study’s senior author, with plans to commercialize both a research platform and a consumer health product. The test may become available within two to three years, starting with key organs such as the brain, heart and immune system.
Reference: Oh HSH, Le Guen Y, Rappoport N, et al. Plasma proteomics links brain and immune system aging with healthspan and longevity. Nat Med. 2025. doi: 10.1038/s41591-025-03798-1
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