Evidence is growing that every chromosome in the body carries a marker that counts down from the day of birth to death, rather like a cellular sand clock. These biological timers are telomeres—repeat sequences of DNA that, together with associated proteins, cap the ends of chromosomes and protect them from degradation, just as the plastic coating on the ends of shoelaces stops them from fraying.

Research has shown that telomeres shorten with each cell division, gradually marking off the time to cell death.1 This shortening is accelerated in diseases associated with ageing—particularly cardiovascular disease and cancers—and in the presence of risk factors for these diseases such as obesity and high blood pressure. The hope for the future is that measurements of telomere length could be used to detect early disease, allowing preventive measures to be put in place, and eventually that methods will be found to slow or even reverse the shortening.