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Age affects us all eventually, but聽a聽lucky few seem to stave off the effects of ageing for longer. A聽new blood test may help us understand why.

As well as telling us how fast we are ageing, the test can also predict whether a person is more likely to develop a chronic disease or die in the near future. It is an update on epigenetic clocks, tests that estimate a person鈥檚 biological age based on markers thought to control the way genes are expressed.

鈥淚t鈥檚 like a speedometer 鈥� it tells聽you how fast you鈥檙e going, in聽contrast to clocks, which tell you how far you鈥檝e come,鈥� says Daniel Belsky at Columbia University in New York. This means the new test聽is 鈥渁 more immediate measure of the ageing rate鈥�, he says.

Epigenetic clocks often compare chemical tags on DNA that are markers of gene expression in people of different ages. But these may differ for reasons other than ageing, says Belsky. For example, older people might have had poorer diets or have been exposed to more聽pollutants and pathogens early in life, he says.

To develop the 鈥減ace of ageing鈥� test, Belsky and his colleagues followed 954 people and tracked changes in聽18 markers of health. These included indicators of participants鈥� heart, liver, lung and kidney function, as well as their waist-to-hip ratio, blood lipids and聽markers of inflammation. Each聽volunteer was assessed at聽ages 26, 32, 38 and 45.

The researchers used all this to聽get an idea of the average change in participants鈥� health as they aged and to measure how each person aged biologically. They then used this information to create a single blood test that measures chemical tags on DNA indicating changes in the 18 health markers.

To check whether the test could predict how quickly a person ages, the researchers compared the participants鈥� scores at age 38 with their physical and cognitive health seven years later, when, at age 45, the volunteers took tests of their balance, coordination and cognition and were scored based on how old they looked. 鈥淚n nearly every case, people whose DNA [markers] suggested they were ageing faster were showing these emerging deficits in function,鈥� says Belsky.

Belsky鈥檚 team also applied the聽test to a study that has tracked聽the health of a group of men, now in聽their 70s, since the 1960s. The test predicted who would develop worse health and聽who was likely to聽die in the subsequent seven years. During this聽period, 鈥減eople with a faster [pace of ageing] at baseline were聽at聽increased risk to develop a聽new chronic disease or to聽die鈥�, says Belsky.

The new test represents 鈥渢he best聽we can do鈥� to measure ageing, says Sara H盲gg at the Karolinska Institute in Solna, Sweden. But a lot more data will be needed before it聽can be used in clinical settings, says聽Belsky. As the test is based on聽people of European ancestry living in New Zealand, it will also聽need to be trialled in other populations, says Paul Yousefi at聽the University of Bristol, UK.