You may think you know your age, but your body doesn’t follow a calendar.
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This means that your chronological age, which is the number of years since you were born, may not correspond to your biological age, which reflects your body’s wear and tear at the cellular level.
Based on factors such as genetics, lifestyle, and medical history, you may be biologically older or younger than your chronological age. That’s because these two measures don’t necessarily move at the same pace, said Dr. Douglas Vaughan, director of the Potokusnack Institute on Longevity at Northwestern University Feinberg School of Medicine.
“Every birthday adds another year to your life,” Vaughn said. “We all experience it at the same rate. It’s relentless, relentless, and cosmically indifferent.”
Biological age, also called epigenetic age, on the other hand, is “more reflective of changes within the body that occur over time,” he says.
Scientists have developed various methods to estimate biological age, including the so-called epigenetic clock, which measures changes in DNA at the molecular level. These watches are often created for clinical research purposes and are becoming mainstream in the form of test kits sold directly to consumers.
“We now have a number of tools that can give us some insight into the biological age of a particular individual,” Vaughan says. “This whole field is exploding right now because we now know that there are ways to measure biological age that we hadn’t thought of before.”
As the longevity industry booms, the biological age testing market is growing as well, reaching $1.28 billion worldwide by 2024, according to market research and consulting firm Daintero. It is expected to reach $3.09 billion by 2033.
Biological age test kits are widely available online, ranging from a $299 saliva-based test to a $499 blood test. But not all tests are created equal, and there are limits to the health insights they can provide.
“Epigenetic age measurement is not yet prime time for the general consumer,” Vaughan said. “The data and value of those types of tests are completely uncertain.”
What can the epigenetic clock tell us?
The epigenetic clock is an algorithm based on DNA methylation. Daniel Belsky, an associate professor of epidemiology at Columbia University’s Robert N. Butler Columbia Center on Aging, said the process can be thought of like a dimmer switch that turns genes on and off.
Still, such clocks are primarily designed “without any reference to biology. It’s a purely statistical process,” Belsky said. “Each epigenetic clock has a different label, which has a very important impact on 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 involved in the development of a clock called DunedinPACE that measures the rate of biological aging. (The watch is currently licensed exclusively to TruDiagnostic, a company that sells biological age tests and of which Belsky occasionally serves as an advisor.)
“We’re trying to differentiate between speedometers and odometers,” Belsky said. “The odometer tells you how far you’ve traveled. It’s like your biological age. (DunedinPACE) is the speedometer, it tells you how fast you’re going.”
A DunedinPACE value of 1 means a person is aging at an average rate, Belsky said. A score of 2 means you’re aging twice as fast, and a score of 0 means you’re not aging at all. (Theoretically, a negative value means the person is getting younger.)
“Most people’s values fall between 0.5 and 1.5,” says Belsky. “When it comes to aging, even a 10% difference is a big deal. Even if you only age 11 months out of every 12 years of your life, that’s not bad.”
Biological age is a snapshot
Steve Horvath, a professor of human genetics and biostatistics at the David Geffen School of Medicine at the University of California, Los Angeles, helped develop the first saliva-based epigenetic clock in 2011.
Although the watch has a U.S. patent, “no one is using it, not even me,” Horvath said. “That just wasn’t enough.”
However, his early efforts paved the way for the epigenetic clocks used today. In 2013, he developed the Horvath Clock, a timekeeper that can analyze various tissues and cell types, and received patents in Europe and China. The University of California trustees own all patents related to Horvath’s clocks.
Horvath also helped invent PhenoAge in 2018 and GrimAge in 2019. Many commercially available tests use these markers to estimate biological age.
Horvath emphasized that the primary use of these clocks remains in the laboratory. But he hopes the test may become a routine part of health exams in the near future.
Read more about the science of longevity
“Testing is not done yet because clinical validation hasn’t caught up,” Horvath said. “But very serious medical researchers are testing it to see if it works.”
Given the speed at which longevity science is progressing, “we might change our minds in two years,” he added. “who knows?”
Biological age is more than a number, says Christopher Hein, a principal investigator in his lab in the Division of Cardiovascular and Metabolic Sciences at Cleveland Clinic Research.
“We compare current health status with aging over time in terms of multiple organ systems, metabolism, weight, and bone density,” Hein says. “If you think about the terms ‘life expectancy’ and ‘healthy life expectancy,’ it’s probably the same thing. Life expectancy is the number of years you live, but healthy life expectancy is the number of years you can live without chronic disease.”
Regardless of the type of biological age test, it represents a snapshot in time, Hein said. Something as simple as having a cold can affect your results.
“If you just do it once, it doesn’t mean much, because you don’t know whether you’re on an upward trajectory or a downward trajectory in terms of how quickly you age,” Hein says. “If we had more snapshots of the epigenetic clock, we’d probably get better.”
Considering biological age comprehensively
Hein predicted that biological age tests could play a larger role in medicine sooner rather than later, but cautioned that for the time being they are not aimed at diagnosing disease. Taking a test on a whim isn’t without risks, he says.
For example, someone who believes they lead an active and healthy lifestyle may be shocked to learn that their biological age is five years older than their chronological age, and may take drastic steps to improve their biological age.
“There may be risks for people who are obsessed with slowing biological aging,” Hein says. “Instead of self-diagnosing or self-treating, such as by exercising or taking too many supplements, you may want to see a health care professional for follow-up.”
Northwestern’s Vaughan says that chemical changes in DNA are somewhat malleable. For example, smoking is associated with accelerated biological aging, and studies have shown that taking a daily multivitamin may slow biological aging in older adults.
Belsky also said that it is not uncommon for epigenetic clocks to not match each other, so consumers should interpret test results carefully.
“These are research tools that may provide additional information to curious people,” Belsky said. “Some watches are better at predicting future health outcomes, while others are not.”
Vaughn, a trained cardiologist, said chronological age is the strongest predictor of any disease. Now, he says, biological age could be even better.
“We’ve really refined and improved our ability to think about what puts people at risk for different diseases as they get older,” Vaughan said. However, considering biological age alone “can be misleading and may not be a true guide to health or future well-being.”
Don’t jump to conclusions about biological age test results, especially if they’re positive, Vaughan says.
“If you do a test and find out that your biological age is 10 years younger than your chronological age, that makes for great cocktail party conversation,” Vaughan said. “But what’s your cholesterol? What’s your blood pressure? If you don’t address things like that, you’re going to have problems.”
