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 your birth—might not match your biological age, which reflects the wear and tear your body has suffered at a cellular level.
Depending on factors such as genetics, lifestyle habits, and medical history, you may be biologically older or younger than your chronological age indicates. That’s because these two measures don’t always move at the same pace, according to Douglas Vaughan, director of the Potocsnak Longevity Institute at Northwestern University Feinberg School of Medicine.
“Every time you have a birthday, you add another year to your life,” Vaughan said. “We all experience this at the same rate; it is relentless, inexorable, and cosmically indifferent.”
On the other hand, biological age—also called epigenetic age—“reflects to a greater extent the internal changes that occur in your body over time,” he explained.
Scientists have developed various ways to estimate biological age, including so-called “epigenetic clocks,” which measure DNA alterations at the molecular level. These watches—often created for clinical research purposes—are becoming popular and marketed in the form of direct-to-consumer test kits.
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“We currently have numerous tools that allow us to obtain information about the biological age of a specific individual,” said Vaughan. “This whole field is experiencing an explosive boom right now, as we discover ways to measure biological age that we hadn’t even imagined before.”
Along with the rise of the longevity industry, the biological age testing market is also growing, which will reach a global value of $1.28 billion in 2024, according to the market research and consulting firm Dataintelo. This figure is projected to reach $3.09 billion by 2033.
Biological age testing kits are widely available online, with prices ranging from $299 for saliva-based tests to $499 for blood tests. However, not all tests are created equal, and there are limitations to the health information they provide.
“Epigenetic age measurement is not yet ready for the general public,” Vaughan said. “The data and value of this type of testing 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 Center on Aging at Columbia University, can be thought of as a dimmer switch that turns genes on and off.
However, these clocks are largely designed “without any reference to biology. It’s a purely statistical process,” Belsky said. “The labels of different epigenetic clocks vary, and this has very significant consequences for the meaning of each clock.”
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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 over the course of a year.
In 2022, Belsky participated in the development of a clock called DunedinPACE, which measures the rate of biological aging. (This watch is currently exclusively licensed to TruDiagnostic, a company that markets biological age testing and for which Belsky occasionally serves as a consultant.)
“We often make the distinction between the speedometer and the odometer,” Belsky explained. “The odometer tells you how far you’ve traveled; that’s your biological age. (DunedinPACE) is your speedometer: it tells you how fast you’re going.”
A score of 1 on the DunedinPACE means the person is aging at an average rate, Belsky said. A score of 2 would indicate that you are aging twice as fast, while a score of 0 would mean that you are not aging at all. (In theory, a negative value would imply that the person is getting younger.)
“Most people’s values are between 0.5 and 1.5,” Belsky said. “Even a 10% difference in the aging process is a significant change. If you only age 11 months for every 12 you live, that’s not bad at all.” Biological age is a snapshot
Steve Horvath, a professor of human genetics and biostatistics at the David Geffen School of Medicine at UCLA, helped develop the first epigenetic clock in 2011 using saliva.
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Although it has a patent in the United States, “no one uses this watch; no one, including me,” Horvath said. “It just wasn’t good enough.”
However, their early efforts paved the way for the epigenetic clocks used today. In 2013, he created the Horvath Clock, a time meter capable of analyzing various tissues and cell types, which is patented in Europe and China. The Regents of the University of California own all patents associated with Horvath watches.
Horvath was also involved in the invention of PhenoAge in 2018 and GrimAge in 2019. Several over-the-counter tests use these markers to estimate biological age.
Horvath stressed that the primary use for these watches remains in the laboratory. However, he hopes that in the near future these tests will become a regular part of medical examinations.
