A few years ago, scientists discovered that certain chemical changes to our DNA which accumulate over time can be used to predict our age. Now, taking this one step further, researchers have found that the difference between this estimated age and our actual, chronological age, can be used as a kind of “biological clock” to predict our lifespan. Unfortunately, even after taking a variety of different factors into consideration, the researchers found that if a person’s estimated age is higher than their chronological age, then they are more likely to die sooner than individuals whose ages match up.

The DNA modifications that the researchers used to estimate an individual’s age are a type of epigenetic change. These are changes that result in alterations in gene expression, such as switching genes on or off, without actually modifying the DNA sequence itself, like a mutation. In this case, the researchers were looking at DNA methylation, which involves the addition of a chemical tag at certain sites along the sequence.

It’s well-known that the degree of DNA methylation changes as we age and that levels can be influenced by lifestyle, environmental and genetic factors. Cigarette smoking and acute stress, for example, have been shown to alter DNA methylation.

Earlier studies found that DNA methylation can be used to estimate an individual’s age and that differences between this predicted age and actual chronological age may be associated with risk for age-related diseases and mortality. However, no studies had investigated whether DNA methylation is strongly linked to an individual’s lifespan.

To find out if this is indeed the case, scientists from the University of Edinburgh, in collaboration with researchers in Australia and the US, used data from four independent studies which followed the lives of almost 5,000 individuals for up to 14 years. In order to measure their DNA-methylation age, or estimated age, scientists looked for markers in the participants’ blood which was taken both at the outset and throughout the duration of the study.

As described in Genome Biology, the researchers found that having a DNA-methylation age five years higher than your actual, or chronological, age, is associated with a 21% higher risk of mortality, or death from all causes, even when age and sex were taken into consideration. However, if researchers took into account a variety of other environmental and lifestyle factors, such as education, smoking, diabetes, cardiovascular disease and social class, the increased risk of mortality was reduced to 16%.

Although this study suggests that a link exists between this “biological clock” and mortality, further investigation is required to clarify what specific factors—environmental, genetic or lifestyle—influence a person’s biological age. However, the researchers already have some studies in the pipeline which will hopefully shed light on this.

“This new research increases our understanding of longevity and healthy aging,” lead scientist Professor Ian Deary said in a news release. “It is exciting as it has identified a novel indicator of aging, which improves the prediction of lifespan over and above the contribution factors such as smoking, diabetes and cardiovascular disease.”

[Via University of Edinburgh, Genome Biology]