Last week, I saw a doctor post their BioAge online, treating it like a lab result. Now, gyms, fitness trackers, and mail-in kits all give you some version of your ‘age.’ I wanted to find out how these numbers are really calculated.
What?
Let’s start with the most reliable method. A USC-led study published in npj Aging on July 20 tested the five most popular epigenetic clocks on 3,227 adults from the Health and Retirement Study. These clocks, Horvath, Hannum, PhenoAge, GrimAge, and DunedinPACE, did not share a single gene in common. The authors said there were “more unique than common biological processes.”
These clocks can also give inconsistent results. A 2022 study in Nature Aging found that technical noise alone could make six of these clocks show up to a nine-year difference when testing the same sample twice. Newer versions have reduced this gap to about 1.5 years, so there is a fix. Still, most reports don’t say which version was used for your result.
Consumer options are even less accurate. EGYM gym machines use four fitness tests: strength, cardio, metabolism, and flexibility. WHOOP figures out your age from months of sleep, training, and recovery data. Garmin mostly uses your VO2max. This means the same person could get three different ages from three devices.
So what?
None of these tools truly measure aging. They look at your fitness and habits, then turn those results into years, since that’s a number people understand.
I think that’s okay. If a simple number gets someone to go to the gym on a Tuesday, that’s more useful than a perfect measurement no one pays attention to. Treat it like a game. If your watch pushes you to work out a fourth time this week, it’s working.
The problem is when doctors present a vendor’s score as if it’s a real lab result. Then the suggestion becomes a claim. Most people can’t tell the difference. That’s why credentials matter, and using them to support an unproven number isn’t a good idea.
Now what?
See your ‘age’ score as a tool to track your habits, not as something for your official health record.
Focus on the numbers behind the score: your VO2max (in ml/kg/min), strength, waist size in centimeters, and blood pressure. Each of these can predict health outcomes by itself.
Only compare your results to your own past results, using the same device and the same conditions. Numbers from different brands can’t be compared.
If you get a score, ask your provider two questions: Has this score been tested against illness or death in people outside their database? And which version of the clock are they using?
If a gym blood pressure cuff shows 140/90 or higher, check your blood pressure at home over several days. The 2024 European Society of Cardiology guidelines recommend out-of-office readings before making a diagnosis.
I made a similar point in July about the supplements in your cupboard. You can read more in The Doctor’s Edit on Your Longevity Drawer (https://www.andreheeg.com/archive/the-doctors-edit-on-your-longevity-drawer).
Let the number motivate you to go to the gym. That’s its only purpose.
Stay healthy.
Andre