Biological Age / Chronological Age
Issue 1 — Cover Story
Biological
Age?
Earlier this week, I rang in my 44th birthday in Sydney. I winced each time my eight year-old daughter incremented as she sang me "are you one, are you two, are you three," and so on, all the way up to 44 - which, painfully, took more than a few minutes - a nice reminder that I'm not as young as I sometimes (oftentimes) convince myself that I am.
And yet, somewhat remarkably, I'm entering this new year of my life feeling better than ever. I feel fit, loose, healthy, and energized - on many days, even more so than I did in my 20s.
It reminded me of just how one-dimensional what we colloquially refer to as "age" really is, namely chronological age (CA), an objective measure of time since birth. While CA only measures the passage of time, Biological Age (BA), a growing metric in longevity medicine, offers a more nuanced reflection of our health and aging.
With BA's growing relevance has come significant informational overload all across the academic literature, Instagram and TikTok, as well as on podcasts. It's our goal in this newsletter to elucidate much of the information surrounding BA, including the types, its role in longevity medicine and how wearables have entered the realm of BA.
Biological Age (BA) is a measure of how fast your cells, tissues, organs and organ systems are aging. This, understandably so, may seem vague at first glance, and rather abstract compared to chronological age, simply the number of years passed since birth. But as I hope you'll see, it allows for a much more nuanced, in-depth and informed analysis of longevity, and equally as important, how well our anti-aging interventions may be working.
In short, I think of BA as a composite of biological parameters (aging biomarkers) that better predicts functional capabilities in later life than chronological age. What should be abundantly clear, both from my definition and the AFAR's criteria, is that there's no single marker for BA in the way CA simply has the year. This is really important. CA is fixed and definitive, which is likely why it's become the default measure of age. BA, by contrast, will never be that clean or absolute, for better or worse - inherently, it's a composite of multiple markers, not just one.
While scientists and physicians - myself included - prefer to use jargon like biomarkers and parameters, most people simply opt for clocks when talking about the types of BA parameters that exist. The three most popular clocks are as follows:
| Name | Measurement | Specs & Longevity Relevance |
|---|---|---|
| Epigenetic Clocks | DNA methylation levels at specific sites across the genome | The two most well studied algorithms are the Horvath and Hannum clocks. Higher BAs calculated from these algorithms relative to CA has been associated with increased risk of all-cause mortality. |
| Telomeric Clocks | Telomere (repetitive DNA sequences capping chromosomes) length | Telomere length shortens every time cells divide. Thus, shorter lengths are associated with increased mortality risk. Its predictive power appears strongest for head and neck cancers, as well as coronary heart disease. |
| Phenotypic Clocks | Multiple clinically-observable biological and physiological markers | Use routine biomarkers like glucose, creatinine, and white blood cell count. Highly actionable through lifestyle changes, offering insight into longevity at a broader, systems level. |
It goes without saying that none of these are perfect. Each has its limitations based on the available scientific literature. The importance here is not to get bogged down in the scientific specs, but rather to demonstrate again that BA is a composite measure, and that each clock estimates BA in radically different biological fashion.
To learn how these biological age clocks perform independently, and how well they confer with one another, I decided to test my own BA using each of the above methods - and then added one more: wearables. As a quick disclaimer, this isn't an official scientific study, nor should it be generalized to the entire population. This was simply a fact-finding mission to learn more about my own BA and how well these clock estimates may perform.
There's good news and bad news. Let's start positively: my telomere test came back at 37, and my phenotypic age landed at 31 - 13 years younger than my chronological age of 44. The wearables - Garmin, WHOOP, and Oura - were broadly aligned with that trend, estimating me to be about 4-5 years younger based largely on cardiovascular and activity data.
| Clock | Epigenetic | Telomeric 1 | Telomeric 2 | Phenotypic 1 | Phenotypic 2 | Wearable (avg) |
|---|---|---|---|---|---|---|
| Age | xx | xx | xx | xx | xx | xx |
Soul crushingly, not all results pointed in the direction of youth. One company that assessed all three lab-based measures told a very different story: 50 via methylation, 54 phenotypic, and 56 based on telomere length. Ouch. In total, my biological age varied by nearly 25 years depending on the method used. These clocks all measure BA, but the manner in which they do so radically differs - and it shows in my results. Use them as context, not conclusions.
This is where interpretation becomes critical.
If you're interested in how I approach this in practice:
Learn more about how I approach longevity medicine →Everyone is tracking everything with a Garmin, Oura Ring, or some other smart wearable. These devices are everywhere, and many now provide estimates of BA. But the way they calculate BA is quite different from the lab-based tests described in the earlier "Types" section.
Take Garmin, for example, and its "Fitness Age" metric, which it defines as an "interpretation of your VO2 max estimate." Garmin couples this estimate with other factors like resting heart rate, age, sex, and activity patterns, to produce a single age-equivalent number. How each factor is weighted, however, is - likely intentionally - unclear. There exists no publicly available algorithm that details how this BA estimate is calculated.
While these wearable metrics can be useful, it's important to understand that Fitness Age is a composite estimate derived from an interpretation of multiple other estimates, calculated in a way that remains opaque. Unlike the BA clocks we discussed earlier, which use actual blood samples and well-documented, peer-reviewed algorithms, wearables, as of now, do not. The gold standard of established, biomarker-based clock types is still a standard above those calculated by wearable devices.
BA has potential to be an incredibly useful metric. And this, importantly, is all that it should be. BA, as well as the wide array of health metrics that we are all gaining increasingly easy access to via clinics and wearables, are, at the end of the day, measurements. That is all. They are not targets. Nor are they goals for us to strive for, clinician or patient. Using them as such creates a dangerous cycle of incomplete evidence and fragmented postulation that can result in misinformation. How we use and think of BA is of equal importance to what BA fundamentally is; it's an incredible measure, not a goal, helping us understand how well our anti-aging protocols and longevity interventions are working.
At LMI, we don't treat biological age as a target, but as a signal to interpret.
If you're considering a more personalised assessment, you can speak with our team to understand which approach may be most appropriate for you:
Request a private consultation →by Dr. Adam Brown
