People curious about their “biological age” are flocking to longevity clinics and buying online tests in hopes of understanding how their bodies are aging. Unlike chronological age, which is fixed based on birth, biological age reflects the condition of a person’s cells, tissues, and organs, and could provide insight into overall health, experts say.
Tony Wyss-Coray, a Stanford neuroscientist who studies aging, describes biological age as a measure of “intrinsic capacity,” or how well the body functions compared with its years. “What is the intrinsic capacity of the cells or tissues in your body? How well are they functioning compared to how old you are?” he asks.
The U.S. government recently launched an initiative to identify accurate and reliable ways to measure biological age, joining a global race among companies and researchers. Current methods, often called “biological-age clocks,” use blood or saliva tests, protein patterns, wearable device data, or even scans of the retina and facial features to estimate age. Some tests analyze grip strength or voice patterns.
Dr. Eric Verdin, president of the Buck Institute of Aging Research, says the field is expanding rapidly. “Biological age is the shiny object on the hill that everyone wants to measure and determine,” he says. While some people, including Verdin himself, use these clocks to track personal health, he cautions the tools are still largely experimental.
Tech entrepreneur Bryan Johnson, who follows a strict longevity routine, claims he ages only six months per year according to one clock, crediting diet, exercise, and supplements. But experts warn that most consumer clocks are not proven to measure biological age accurately. Martin Borch Jensen, founder of Norn Group, calls current tests “consumer longevitainment” and stresses that clocks must be interpretable, showing a clear link between test results and biological aging.
Reliable clocks could revolutionize medicine and drug development. Without accurate measures, testing anti-aging therapies in humans is slow and costly. Researchers are exploring organ-specific clocks and AI-driven analyses to track hundreds of biomarkers, from proteins to metabolites, to identify which changes predict health outcomes or longevity.
The U.S. Advanced Research Projects Agency for Health (ARPA-H) is funding efforts to validate clocks that could serve as surrogate markers for aging. “We need a biomarker that can serve as a surrogate for natural aging that could tell you that answer in two or three years,” says Andrew Brack, leading the initiative, which will also explore drugs with potential longevity benefits.
Wyss-Coray is pioneering organ-specific clocks that estimate the age and function of individual organs, which could allow for personalized interventions. He hopes these tools will soon be used in clinics to provide preventative care and feedback to patients. “The major hope is that we will be able to do preventative medicine and give people real feedback about whether treatments and other interventions are working to improve their health. It could completely change medicine,” he said.
As the field evolves, scientists warn consumers to treat current clocks with caution, while anticipating more precise and clinically useful tools in the coming years.
