An astronaut who spent nearly a year in the International Space Station experienced changes to his body which appeared to reverse one of the key ageing processes, according to new research.

Scott Kelly, who has an identical twin who is a retired astronaut, spent 340 days on the space station in 2015 and 2016.

Scientists used the opportunity to monitor changes in Mr Kelly’s body while he was in space compared to those experienced by his brother Mark.

What they found was surprise.

​Telomeres, which are involved in the repair of damaged DNA, fluctuate in length but gradually get shorter as people get older, decreasing their effectiveness and increasing the risk of cancer.

But those in Mr Kelly’s white blood cells seem to have got longer than his brother’s while he was living in the Space Station.

“That is exactly the opposite of what we thought,” radiation biologist Susan Bailey told Nature.

The extra radiation that astronauts are exposed to in space was expected to have led to shortening of the telomeres.

The scientists were so surprised that they had sent the samples to another laboratory to double check the results.

A study involving 10 astronauts is now underway in an attempt to work out what happened.

It might have nothing to do with life in space.

An article about the ongoing research into the effects of space on Mr Kelly’s body posted on Nasa’s website said it “could be linked to increased exercise and reduced calorie intake during the mission”.

“However, upon his return to Earth they began to shorten again,” the article said.