Aging · Epigenetics
One methylation clock reads age across nearly every human tissue
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Short answer
353 CpG sites predict chronological age across most human tissues from one model, and read near zero in pluripotent stem cells.
What happened
Horvath trained an elastic-net predictor on 7,844 non-cancer Illumina methylation samples drawn from 82 public datasets, then validated it across tissues. The resulting 353 CpG sites track chronological age across brain, blood, breast, kidney, liver and more, from a single model. Embryonic and induced pluripotent stem cells are estimated near zero, and reprogramming resets the estimate.
Why it matters
Before this, age estimators were tissue-specific — a blood clock did not read liver. A single multi-tissue model implies the methylation changes it tracks are part of something shared across cell types, which is why the clock became a standard tool for studying aging rather than a curiosity.
Evidence
- Study type
- Elastic-net penalized regression trained and validated on public Illumina methylation datasets
- Sample
- 7,844 non-cancer samples from 82 datasets; cancer sets analysed separately
- Journal
- Genome Biology · peer reviewed
- Replication
- Widely reproduced and extended, including the three-CpG blood estimator also in this corpus
- Limitations
- Accuracy varies by tissue and by disease; the clock is a predictor, not a mechanism, and resetting it has not been shown to reverse anything.
What this connects to
Sources
The 2 studies this explanation is built from, by the role each plays. Every source links to PaperFren’s explanation of it and to the original paper.
Supporting evidence
- Three CpGs track blood aging
Age-related blood DNA methylation at a few CpGs predicts chronological age with ~3.3-year MAD.
What it does not showLimitations
Does not prove CpG changes cause aging diseases.
PaperFren explanationStudy with cards and a quizOriginal paper (DOI)cc by
Landmark research
- A DNA methylation clock for human age
A 353-CpG epigenetic clock predicts age across diverse human tissues.
What it does not showLimitations
Not a causal aging therapy; accuracy varies by tissue/disease.
PaperFren explanationStudy with cards and a quizOriginal paper (DOI)cc by
Before
Epigenetic age estimators were built and validated within single tissues, usually blood, and were not expected to transfer.
Now
A multi-tissue clock works, which reframes methylation drift as a systemic phenomenon. It predicts age; it does not show that methylation causes aging, and its accuracy varies by tissue and disease state.