A person's true age can be discovered simply by shaking hands, researchers claim.

Scientists found hand-grip strength correlated with known markers of ageing such as disability, mental decline, recovery time after hospital treatment, and death.

They believe a "handshake test" could be used as a viable test for biological age.

"Hand-grip strength is easily measured and data on hand-grip strength now can be found in many of the most important surveys on ageing worldwide," said Dr Warren Sanderson, a member of the team from the International Institute for Applied Systems Analysis (IIASA) in Austria.

The research, published in the online journal Public Library of Science ONE, reviewed findings from more than 50 studies looking at people of all ages from around the world.

It found that higher grip strength corresponded with indicators of younger biological age in different population groups.

Co-author Dr Serguei Scherbov, also from the IIASA, said: "We found that based on this survey, a 65-year-old white woman who had not completed secondary education has the same hand-grip strength as a 69-year-old white woman who had completed secondary education.

"This suggests that according to hand-grip strength characteristic their ages are equivalent and the 65 year-old woman ages four years faster due to lower education attainment."

Previous research has shown that simply measuring the number of years people have lived does not provide an accurate picture of biologically how old they are.

Dr Scherbov added: "Our goal is to measure how fast different groups in a society age. If some group is getting older faster than another, we can ask why that might be and see whether there are any policies that could help the faster ageing group."