‘I did read in the newspaper the other day … that seven per cent of my DNA had changed permanently,’ he said.
‘And I’m reading that, I’m like: ‘Huh, well that’s weird’.’
Scientists suggest that the changes are the result of the extreme stresses Kelly’s body was subject to during his stay on the ISS.
‘Oftentimes, when the body encounters something foreign, an immune response is activated,’ Dr Christopher Mason, a Twins Study researcher and an associate professor at Weill Cornell Medical College, told Business Insider.
‘The body thinks there’s a reason to defend itself. We know there are aspects of being in space that are not a pleasant experience, and this is the molecular manifestation of the body responding to that stress.’
Nasa published its preliminary findings from the Twin Study last year, but has now released the results of a number of new studies.
The agency has now confirmed that Kelly came home 5 cm (2 inches) taller than his twin – a change had resolved itself within two days of his return.
The height difference was caused by the ISS’ microgravity conditions which elongate the spine – but the effect was only temporary.
They have also verified that Kelly’s telomeres – the caps on the ends of chromosomes – grew to be longer than Mark’s.
Telomeres are involved in the repair of damaged DNA and key to preventing ageing, and the find may help us better understand how and why we age.
Nasa said in a statement: ‘Nasa has a grasp on what happens to the body after the standard-duration six-month missions aboard the International Space Station, but Scott Kelly’s one-year mission is a stepping stone to a three-year mission to Mars.
‘By measuring large numbers of metabolites, cytokines, and proteins, researchers learned that spaceflight is associated with oxygen deprivation stress, increased inflammation, and dramatic nutrient shifts that affect gene expression.
‘The Twins Study has benefited Nasa by providing the first application of genomics to evaluate potential risks to the human body in space.