Quick, how old are you? Chances are, the answer that springs first to mind corresponds with the number of candles on your last birthday cake. But our bodies age in uniquely individual ways, and chronology is only one way — if a simple and universally accepted one — of looking at our lives.

Now, sophisticated new methods for quantifying "biological age," offer the chance to, at least in theory, challenge what the calendar tells us. But are these enticing testing services offering us a chance to optimize our health and get a jump on early risk factors for diseases and chronic conditions — or are they just a tool for quantifying (and exploiting) our terror of growing older?

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The concept of biological age is a fairly new one, one whose recent popularity is credited largely to UCLA professor Dr. Steve Horvath. In 2013, Horvath proposed the idea of an "epigenetic clock … to address a host of questions in developmental biology, cancer and aging research." Epigenetics examines how external factors interplay with your genetic makeup. You can't change your DNA any more than you can change your birth date, but for better or worse, your behavior can influence your health. Exposure to UV radiation and human papillomavirus, for example, can mutate your DNA, but it's not like you can schedule an appointment with a geneticist to become a member of the X-Men.

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For most of us, this basic knowledge has come in the form of our doctors telling us to quit smoking, or the realization that we feel better when we eat more fiber and get enough sleep. But now, in our data-driven world, we can — if we have the inclination, the money and the willingness to take a blood and/or urine test — go deeper.

A growing consumer market for home test kits which promise to help you "take control of how you age" — and can run upwards of $300 for a single kit, not to mention $130 a month for personalized "action plans," supplements not included. The overall genetic testing market is a nearly $2 billion a year business, with a recent Precedence Research report grimly explaining that "The increased prevalence of various chronic diseases among the majority of the population, coupled with increased consumer expenditure on healthcare, has exponentially boosted the market growth." But what are you really getting for your money with these things?

"These bio age testing kits assess various biological markers within your body," explains Dr. Johannes Uys, a general practitioner working at Broadgate General Practice in London. "Factors like telomere length, DNA methylation patterns, and biomarkers related to one’s metabolism, inflammation and cellular health are generally analyzed in bio age tests. The idea behind these kits is that an individual can make lifestyle changes once they understand their bio age better, potentially slowing down the aging process and improving their mental and physical well-being."

"The accuracy and effectiveness of these tests remain speculative, with research and debate ongoing."

Uys notes that "There’s little doubt that these tests have been gaining popularity in recent years," but adds, "That being said, the accuracy and effectiveness of these tests remain speculative, with research and debate ongoing. Bio age tests have their critics, with many arguing that the concept of bio age is a complex matter. We do not have a universally agreed-upon method for its accurate measurement, making it difficult to validate the effectiveness of these kits with definite accuracy."

It's also notable how these kits are marketed, usually putting the word "age" front and center. It may all be in service of tracking your health, but you can't overlook the clear incentive for bragging rights on a playing field where youth triumphs over everything else. 

That doesn't mean that these kits are aren't useful, both for consumers and researchers alike. Gil Blander, the chief scientific officer of the biological age testing and wellness company InsideTracker, wants consumers to recognize what these tests can and can't do. Speaking to me while in the midst of a winter cold, he cites a personal example. "When you're sick, you have a increase of a specific population of cells, for example, lymphocytes," he explains. "When you have them, these kinds of cells tend to be older than other kinds of cells. It doesn't mean that when you're sick, you're getting older, and then a week later, you are getting younger again." 

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But when used and assessed properly, Blander says that these tests can flag biomarkers for certain conditions that you can start making lifestyle interventions around.

"Let's start with the genetic predisposition for genetic diseases," he says. "You can do DNA testing and find whether you have a predisposition for high cholesterol, high glucose. Genetic tests can provide you a clue." But, Blander explains, "Even if you have high risks for cholesterol, 80% of that is under your control, using lifestyle and nutrition and exercise. The problem with our health care providers is that they are treating disease; they are not preventing disease."

He pointed to the term "healthspan," explaining "It means you will live until your last moment in good health. And that's what we're trying to do here." 

Xiaojing Yang, lead scientist for myDNAge, notes another, wider appeal for the boom in biological age testing. "Aging research is a serious scientific topic," she says. "We go into this field for public health. We understand our global population getting older, and we really want to study why people age and how can we understand that aging process better, to help general population become healthier."

She explains, "This [testing] is a quite new thing, about ten years. Before that, your chronological age was nearly the only risk factor for a lot of diseases — cancer, diabetes, cardiac disease. But we're seeing more and more research showing that epigenetic age, in certain cases, can be a stronger, more accurate factor. You can see that if your epigenetic age is younger, you should be at lower risk for certain diseases. I don't think we're going to replace the routine health check, but we're on the way to utilizing this molecular technology to give you early indicators, before any syndrome is detected, for observation." And she says, "No matter whether there are solutions or not, my vision for this work today is that I would like to tell you the risks earlier."

"We're seeing more and more research showing that epigenetic age, in certain cases, can be a stronger, more accurate factor"

We're all innately curious about ourselves. You need only look to the explosive popularity of ancestry and DNA tests as evidence. I've certainly been intrigued by the notion of finding out how old I "really" am. But I also know that it's complicated. After my last physical, I could see from my labs that my blood pressure, BMI and glucose levels are all healthy and have been holding in the same range for several years. I also have been diagnosed with (and treated for) early onset osteoporosis, giving me the bone density of a person decades older.

So I guess at this point I'm not sure if a $300 kit could tell me something helpful that I don't already know, or if this graying Gen Xer would just want to buy some reassurance that she's winning at aging. More significantly, I'm doubtful of how far back I could turn the clock even if I really threw myself into the effort. 

A recent New York Times profile of 46 year-old entrepreneur Bryan Johnson noted his elaborate diet and fitness routine, as well as his fixation on meticulously testing and documenting different markers of his age, from his hearing to his wrinkles to his heart health. And it noted that  "His 'biological age,' he claimed until recently, is 42.5. ... In other words, he has spent about three years shaving off — maybe — a little more than three years." Three years and, by his own count, "millions of dollars."

A 2020 episode of Netflix's "The Goop Lab" produced similar results, as Gwyneth Paltrow and two of her colleagues experimented with a "health-span plan," to "extend youth." And after a truly horrendous sounding, incredibly restrictive cleanse, one that she said made her feel "dying and hangry," she had shaved off a mere 1.7 years from her biological age. And she's Gwyneth Paltrow.

If it's all a numbers game, that's not much of an incentive. Maybe if I had a compelling concern about my lifestyle choices or a genetic risk I didn't think my healthcare team was addressing, I might invest in a bio age kit. For now, anyway, I'd rather save my money, take my chances, and just be the age it says on my driver's license.