You may think you know how old you are, but your body doesn’t follow a calendar.That is, your chronological age, which measures how many years have passed since you were born, may not match your biological age, which reflects wear and tear on your body at a cellular level.Based on factors including genetics, lifestyle habits and medical history, you may be biologically older or younger than your chronological age. That’s because these two measures don’t always progress at the same pace, according to Dr. Douglas Vaughan, director of the Potocsnak Longevity Institute at Northwestern University’s Feinberg School of Medicine.Advertisement“Every time you have a birthday, you add another year to your life,” Vaughan said. “We all experience that at the same rate, and it’s relentless, it’s unforgiving, it’s cosmically indifferent.”On the other hand, biological age, also called epigenetic age, “reflects more of the changes inside you that occur over time,” he said.Scientists have developed a number of ways to estimate biological age, including so-called epigenetic clocks that measure changes to DNA at the molecular level. These clocks, often created for clinical research purposes, are becoming mainstream in the form of direct-to-consumer test kits.“We have lots of tools now that allow us to get some insight into a given individual’s biological age,” Vaughan said. “This whole field is exploding right now, as we learn that there are ways to measure biological age that we never even thought about before.”AdvertisementAdvertisementAs the longevity industry booms, so too does the biological age testing market, which reached $1.28 billion globally in 2024, according to market research and consulting firm Dataintelo. It’s projected to reach $3.09 billion by 2033.Biological age test kits are widely available online, ranging from $299 saliva-based tests to $499 blood tests. But all tests aren’t created equally, and there are limitations to the health insights they provide.“The measurement of epigenetic age is not prime-time yet for general consumers,” Vaughan said. “The data and the value of those kinds of tests is quite uncertain.”What can epigenetic clocks tell us?Epigenetic clocks are algorithms based on DNA methylation. This process, according to Daniel Belsky, an associate professor of epidemiology at the Robert N. Butler Columbia Aging Center at Columbia University, may be thought of as a dimmer switch that turns genes on and off.AdvertisementAdvertisementStill, such clocks are largely engineered “without any reference to biology. It’s a purely statistical process,” Belsky said. “The labels for different epigenetic clocks are different, and they have very significant consequences for what that clock means.”For example, a clock called PhenoAge estimates biological age. GrimAge — a clock named after the Grim Reaper — reflects the probability that a person will die within a year.In 2022, Belsky was …
