Podcast episode 81 (in German)
Epigenetic clocks – what the test measures, and what it cannot tell you
September 19, 2026
A finger prick, around 200 euros, and 3 weeks later a number appears in an app: your biological age. The science behind it is real — it was just built for groups, not for the individual person holding the test kit.
What it is about
With age, the methylation marks on DNA shift in a remarkably systematic way, and clocks can be built from this. The episode goes through their three generations: the first, trained on calendar age, the second, aimed at disease and mortality, and the third, which no longer measures the state but the pace of ageing. Then comes the uncomfortable question of what such a value is worth for an individual, what a much-cited rejuvenation study with nine participants really shows, and which freely available markers deliver a large part of it for a fraction of the money, without shipping and waiting time.
Key points
- The 2013 clock uses 353 methylation sites and hits calendar age across almost all tissues to within 3.5 years on average.
- The second generation adds blood values or was trained directly on mortality, and predicts it better in cohorts than calendar age.
- The pace clock comes from a New Zealand cohort in which around 1,000 people of the same age have been followed for over 50 years; at 45, their biological ages were decades apart.
- This third generation estimates how many biological years are used up per calendar year — 0.8, say, or 1.2.
- The most-cited rejuvenation study, TRIIM, ran for 1 year, turned the clocks back by 2.5 years on average and had 9 participants, all male, without a placebo group.
- PhenoAge can be calculated from 9 standard lab values of an ordinary blood count, and the calculators for it are freely available.
- Home tests range roughly between 100 and 350 euros; most convincing are providers that use a published clock and disclose their methodology.
Where the data stop
The clocks are calibrated on cohorts, not on individual people. For an individual, the confidence interval is several years wide, and with the older methods the same blood sample, measured twice, could differ by years. Newer methods have improved this considerably, but a single value remains a blurry snapshot: an infection, acute stress or the cell composition of the sample shift the number.
It is also unresolved whether the clocks measure ageing or something that accompanies it. There is nice circumstantial evidence — identical twins of whom the smoking one ages faster, children of centenarians who tick more slowly, clocks that jump back during cell reprogramming. None of it is conclusive. And for the test you can order, there is no study in humans that has checked whether people can do anything with the number. Some providers use their own unpublished clocks and also sell the product that supposedly lowers the number.
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Published on September 19, 2026.
The topic in the database
- Precise genetic analyses for personalized health and prevention approaches.Genetic testing
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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-10-09.