Epigenetic clock

An algorithm that estimates biological age from chemical methylation marks at specific sites in a person's DNA.

• Methyl groups on DNA shift in consistent directions with age at certain sites; a model trained on thousands of people learns the pattern.
• Horvath's 2013 clock used 353 sites and estimates calendar age to within about 3–4 years.
• Newer clocks such as GrimAge and DunedinPACE are trained on health outcomes and predict disease and death better.
• A treatment that shifts the marks may not improve health, different clocks disagree, and single readings are noisy.