Methylation of DNA is the best-known mode of epigenetic regulation (turning genes on and off). Methylation patterns are stable unless they are actively changed, and can persist over decades, even across generations.
Four years ago, biostatistician Steve Horvath of UCLA identified a set of 353 methylation sites that are best-correlated with human (chronological) age. These are sites where genes are turned on and off at particular stages of life. A computer analysis of a gene sample (from blood or skin or even urine) can determine a person’s age within about two years.
Two reasons the Horvath Clock is important. First, it is the best measure we have of a person’s biological age, so it provides an objective measure of whether our anti-aging interventions are working. Say you’re excited about a new drug and you want to know whether it really makes people younger. Before the Horvath clock, you had to give it to thousands of people and wait a long time to see if fewer of them were dying, compared to people who did not get the drug. The Horvath clock is a huge shortcut. You can give the drug to just a few people and measure their Horvath (methylation) age before and after. With just a few dozen people over a two-year period, you can get a very good idea whether your drug is working.
Second, there is evidence and theory to support the idea that the methylation sites that Horvath identified are not just markers of aging but causes of ageing…
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