Définition
Epigenetics is the study of heritable changes in gene expression that do not involve changes to the DNA sequence itself. Epigenetic modifications — including DNA methylation and histone modifications — are shaped by lifestyle, environment, and aging, and are the basis for the most accurate biological age measurements.
The genome contains the instructions; the epigenome controls which instructions are read, when, and in which cells. Epigenetic modifications act as molecular switches and volume controls on gene expression without altering the underlying DNA sequence. The key mechanisms are DNA methylation (addition of methyl groups to cytosine bases, typically suppressing gene expression), histone modification (changes to the proteins around which DNA is wound, affecting DNA accessibility), and non-coding RNA regulation.
These marks are not permanent — they change in response to environmental inputs including diet, exercise, stress, sleep, toxin exposure, and aging itself. This plasticity is why identical twins become increasingly epigenetically distinct over their lives, and why lifestyle interventions can produce measurable biological age changes within months.
The epigenetic clock, developed by Steve Horvath at UCLA in 2013, uses DNA methylation at hundreds of CpG sites across the genome to estimate biological age with remarkable accuracy. The GrimAge clock, developed subsequently, correlates with mortality risk and disease onset more precisely than chronological age. Commercial tests (TruAge, Elysium Index) now make this measurement accessible to consumers.
Epigenetic age acceleration — biological age greater than chronological age — is associated with smoking, excess adiposity, chronic stress, sedentary behavior, poor diet quality, and alcohol. Epigenetic age deceleration is consistently associated with aerobic fitness, Mediterranean-style diet, adequate sleep, social connection, and low chronic stress.
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