A US scientist has discovered an internal body clock based on DNA that measures the biological age of our tissues and organs.
The clock shows that while many healthy tissues age at the same rate as the body as a whole, some of them age much faster or slower. The age of diseased organs varied hugely, with some many tens of years "older" than healthy tissue in the same person, according to the clock.
Researchers say that unravelling the mechanisms behind the clock will help them understand the ageing process and hopefully lead to drugs and other interventions that slow it down.
Therapies that counteract natural ageing are attracting huge interest from scientists because they target the single most important risk factor for scores of incurable diseases that strike in old age.