Why the Test Can’t Determine Your “biological Age”
Living forever isn’t enough—everyone wants to stay young forever. In most wellness centers, the word “youth” is often used as a synonym for “health,” but you don’t have to be steeped in esoteric wellness culture to want to know how old you really are—or, more accurately, how young you really are. While you may not be able to fight your chronological age, you can find solace in an alternative approach: “biological age.”
The offer is tempting. Submit a sample of blood or saliva, pay a few hundred dollars , and receive a number that supposedly reveals your “true” biological age. The promise is that this age is the one your body actually lives, not the one listed on your driver’s license. If you discover you’re “biologically” 35 instead of 45, you’ve been fooling yourself. If you discover otherwise, the tests are often bundled with supplements, programs, or subscriptions designed to solve your problems.
The real problem is that biological age isn’t a single number that can be measured or calculated, and no test—no matter how promising its scientific basis—can give you a definitive answer about how your body is aging. Here’s what’s really going on inside these tests, what credible research on aging says, and how to approach the growing market of products that promise to quantify your youth.
What does “biological age” mean anyway?
Chronological age is easy to determine: just count the years since birth. Biological age is an attempt to accurately determine how well the body functions relative to this period. Dr. Dan Belsky, an epidemiologist at Columbia University who studies aging, explains it this way: all people move through calendar time at the same rate, but “our body’s state obviously varies.” Since health tends to decline over time, biological age is essentially an estimate of the age at which a person’s physiological integrity—how well their organs and tissues function, how they withstand stress, and how they recover from injury—will be considered typical within a given reference group.
This last point is key. “There’s no absolute, precise biological age because it’s always relative and based on certain expectations,” says Belsky. Saying you’re “biologically 25” only makes sense when you know the factors by which you’re being assessed and the standards against which you’re being compared. Biological age is a construct built on a specific reference population, which can be a large, nationally representative sample or a much smaller research cohort. This detail is crucial for understanding how much weight should be given to any individual outcome.
There is no single biomarker that determines your “true” age.
Consumer biological age tests often reduce aging to a single number, but researchers studying aging combine multiple types of data to get any meaningful picture. This typically includes laboratory biomarkers, such as blood tests that a doctor may order during an annual physical. These biomarkers are then compared with clinical measurements such as blood pressure, heart rate, and imaging data. Increasingly, researchers are also studying molecular and cellular markers, including genes and proteins.
One of the most discussed approaches in recent years uses an “epigenetic clock,” which analyzes chemical modifications of DNA (rather than the DNA sequence itself) and compares the resulting data to population averages to estimate biological age. Several companies now sell consumer versions of this technology, typically priced around $300 , using blood or saliva samples.
According to Belsky, at best, these commercial tests are “a consumer implementation of a research tool.” In practice, this means the lab takes an algorithm developed based on a specific research dataset and applies it to your individual sample. The algorithm was designed to describe patterns across different groups, not to diagnose an individual, and that’s why a single test result can yield an unreliable individual verdict.
What can (and cannot) influence a person’s biological age.
When it comes to what actually influences biological aging, the answer is “almost everything,” says Belsky. Genetics plays a role in how resilient a person’s body is over time. But environmental and behavioral factors are often just as important, if not more so. The quality of the water you drink and the air you breathe, your diet, and the stability and significance of your social relationships are crucial. Sleep, exercise, and nutrition tend to dominate the public discussion, and for good reason, but they are part of a much longer list of factors that influence aging.
Here, biological age intersects with inequality . Research consistently links poverty, environmental pollution, and unstable living conditions with accelerated biological aging and reduced life expectancy. Not everyone has equal access to fresh food, clean air, safe housing, or reliable medical care—and these differences manifest themselves in the body over time. A biological age test cannot account for the structural characteristics of a person’s body; it can only reflect subsequent biological signals.
Is it possible to reverse or slow down the biological aging process?
Here, marketing is ahead of the science. Many products claim that supplements, special diets, or intensive protocols can measurably “reverse” your biological age. Research, naturally, is more cautious. From the perspective of how most people intuitively understand biological age (as a general reflection of the body’s current state), yes, this state can be changed through improved health. But do behavioral, environmental, or pharmacological interventions actually alter the rate of aging at the cellular level in humans? Here, we have “less clarity,” says Belsky.
Of course, a healthy lifestyle overall promotes improved bodily function and likely influences the biomarkers used in these tests. But claims that any product has demonstrated the ability to “reverse” cellular aging based on rigorous, reproducible studies should always be taken with skepticism. Despite the promises of some life-extension experts, there is no evidence that any supplement, cold bath protocol, or red light therapy device will add decades to your life.
It’s also worth rethinking your goal. Healthy aging isn’t just about looking younger than your birth certificate says or avoiding all illnesses. Instead, it might be more productive to consider a broader healthy lifespan: the time you spend actively, productively, and without significant limitations. This means developing habits that help your body adapt to the inevitable changes over time, rather than wasting time, money, your personal life, and your mental health chasing lower test scores.
What you need to know before buying a biological age test
If you’re eager to know your “true” age, consider the result as a simple indicator, not a blanket verdict. “People often want a metric to track their progress toward personal health goals,” says Belsky, “and most validated tests have at least been studied in research settings, so there’s some understanding of how their results relate to disease risk, disability, mortality, and, in some cases, how responsive they are to interventions.” At the same time, “these aren’t stand-alone, one-time measurements that can be trusted to reveal the full truth about your health.” Like any biomedical test, they are subject to bias and error, and they need to be interpreted in conjunction with other health information, ideally with the input of a healthcare professional.
Before spending hundreds of dollars on a biological age test, it’s worth asking yourself a more practical question: let’s say you discover that your body is aging “faster” than your birthday predicts—how would you actually change your behavior? Perhaps a biological age test is just the nudge you need to start forming the habits you’ve been meaning to develop. But if you already have a general understanding of the factors that contribute to long-term health—physical activity, proper nutrition, adequate sleep, stress management, maintaining relationships, quitting smoking, and so on—perhaps you can begin making these changes today, without having to donate blood.