Researchers have discovered a biological clock that could help predict how long a person will live.

Chemical changes in the DNA that take place over the course of one's lifetime can help predict their ages, but comparing patients' actual age with this "biological clock" could reveal how much time they have left, the University of Edinburgh reported.

Researchers determined people whose biological age was greater than their actual age were more likely to die prematurely than those whose ages matched up. The pattern was revealed through four independent studies that looked at a total of 5,000 older people and tracked them for up to 14 years. The participants' biological ages were determined through several blood tests that looked at a modification in the DNA called methylation.

"The same results in four studies indicated a link between the biological clock and deaths from all causes. At present, it is not clear what lifestyle or genetic factors influence a person's biological age. We have several follow-up projects planned to investigate this in detail," said Riccardo Marioni of the University of Edinburgh's Centre for Cognitive Ageing and Cognitive Epidemiology.

Methylation does not alter DNA sequences but can influence which genes are turned on and off at different times. It can also have an effect on which genes occur throughout a person's lifetime.  

"This new research increases our understanding of longevity and healthy aging. It is exciting as it has identified a novel indicator of aging, which improves the prediction of lifespan over and above the contribution of factors such as smoking, diabetes, and cardiovascular disease," said the study's principal investigator, Professor Ian Deary, also from the University of Edinburgh's Centre for Cognitive Ageing and Cognitive Epidemiology.

The findings were published in a recent edition of the journal Genome Biology.