An international team of scientists has found a way to predict how much time you have left - by comparing your actual age to your biological age, a number worked out by measuring chemical changes to your DNA.

The difference between these two numbers can be used as a DNA "clock" to estimate someone's lifespan, the researchers have discovered.

And, we're sorry to tell you this, but if your biological age is higher than your real-life age, you're more likely to die sooner than someone who's biological and real age match up - regardless of your sex, whether you smoke, or have cardiovascular disease.

In fact, the link between a fast-running biological clock and early death was clear across four independent studies, which involved following almost 5,000 people aged over 50 for up to 14 years. 

The research, led by the University of Edinburgh in Scotland, found that having a biological age five years "older" than your real age is associated with a 16 percent increased all-cause mortality risk, even when adjusting for sex, age, health and other lifestyle factors.

And that's a pretty strong link. The results are published in the journal Genome Biologywhere the researchers explain: "The difference between DNA methylation, age and chronological age predicts mortality risk over and above a combination of smoking, education, childhood IQ, social class, APOE genotype [which predicts someone's risk of Alzheimer's], cardiovascular disease, high blood pressure, and diabetes".

But, unfortunately, there's not much we can do about this knowledge just yet.

"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 University of Edinburgh epidemiologist Riccardo Marioni, who worked on the study, in a press release.

In the research, a person's biological age was determined by measuring the amount of chemical modification, known as methylation, that had occurred in their DNA - something that can be measured by biomarkers in the blood.

Unlike a mutation, methylation doesn't actually change the sequence of your DNA, but it does impact which genes are turned on and off and plays an important role in biological processes. Researchers already knew that assessing methylation could be used to estimate someone's age, but this is the first time this factor has been shown to be strongly linked to lifespan.

"This new research increases our understanding of longevity and healthy ageing," said the study's lead author, Ian Deary, in the release. "It is exciting as it has identified a novel indicator of ageing, which improves the prediction of lifespan over and above the contribution of factors such as smoking, diabetes, and cardiovascular disease."

But while being able to predict lifespan definitely sounds intriguing, until researchers work out what we can do to extend that number, I don't think I want to know where my biological clock is at just yet. Ignorance is bliss, right?