Our DNA sequence remains largely stable throughout life, but the way our genes are regulated can change as we age.
One of the best-studied examples involves DNA methylation — chemical marks on DNA that help regulate gene activity. Patterns of DNA methylation change in characteristic ways over time.
Scientists discovered that some of these patterns are so strongly associated with age that they can be combined into mathematical models known as epigenetic aging clocks.
Early epigenetic clocks were remarkably good at estimating a person’s chronological age. This was an important scientific breakthrough: molecular changes in the body could be used to track aging with considerable accuracy.
But estimating chronological age and measuring biological aging are not necessarily the same thing.
Newer epigenetic clocks have therefore been developed to capture more than years lived. Some incorporate biological information associated with health, physical function, disease or mortality.
This means that not every epigenetic clock answers the same question.
A clock may estimate how closely someone’s DNA methylation pattern resembles that expected for their chronological age, while another may be designed to capture biological changes more closely associated with health outcomes.
Understanding which clock is being used and what it was designed to measure is therefore essential when interpreting an epigenetic-age result.
