Amanda Mascareli in Nature:
Greying hair and wrinkles are external signs of aging, but they are not very precise. Now research shows that a code written into the body's epigenome — the chemical tags that modify DNA — can accurately tell the age of human tissues and cells. This ‘clock’ could provide insights into why certain tissues age faster than others, and why those tissues may be more cancer-prone. In the past few years, researchers have been homing in on regions of DNA that accrue lots of chemical tags called methyl groups as people age. Such methylation can selectively switch off genes. “What was not yet known was that one can develop an age predictor that really works well across most tissues and cell types,” says Steve Horvath, a bioinformatician at the University of California, Los Angeles.
…Strikingly, he found that women’s breast tissue accrues methylation in a way that makes it look an average of 2–3 years older than other healthy tissues from the same woman. In women with breast cancer, healthy tissue situated next to diseased tissue appeared to be an average of 12 years older than other tissues in the body. And Horvath found that tissue from 20 cancer types looked an average of 36 years older than healthy tissue.