Nasa found that while 93 per cent of Kelly's genes returned to normal shortly after returning home, seven per cent were permanently altered.
That study focused on how Kelly's genes changed while in space, comparing it to Mark Kelly's gene expression on the ground.
One finding - that his gene expression levels changed by 7percent - triggered a media sensation, with headlines about him "losing" part of his DNA. NASA considers this analysis a high priority because of the eventual plan to send astronauts to Mars for up to 3 years. He was also lighter than Mark, losing muscle.
The full study and documentation will be released in late 2018.
It's believed the disrupted genes were caused by the stresses of space travel, such as oxygen deprivation.
The findings showed that after returning to Earth, Scott started the process of readapting to Earth's gravity. Most of the biological changes he experienced in space quickly returned to almost his preflight status. While most took hours or days, only a few persisted after 6 months.
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The long-term effects of space habitation are still unknown and the space agency said the experiment was a stepping stone for its mission to Mars. Scientists discovered Scott's telomeres - the endcaps of chromosomes that shorten as you age - actually grew longer during his one year in space. While this finding was presented in 2017, the team verified this unexpected change with multiple assays and genomics testing.
Bailey said she was concerned the findings were being "sensationalised". Kelly's transformation suggests longer-term alterations related to at least five biological pathways and functions.
The one-year resulted in no significant decreases in Scott's cognitive performance.
In January, NASA published an update on the studies, while announcing that it meant to release its full findings sometime this year. NASA describes gene expression as "how your body reacts to your environment", and a huge variety of everyday factors - from the amount of exercise a person gets, to the type of diet they eat, to which drugs or toxins they're exposed to - can have an impact. First, there was a significant increase in average length while he was in space, and then there was a decrease in length within about 48 hours of his landing on Earth that stabilized to almost preflight levels. Last year, NASA published its first round of preliminary results at the 2017 Investigator's Workshop.
Observations guide development of future hypotheses. They studied these before, during and after his mission.
NASA's Human Research Program is dedicated to discovering the best methods and technologies to support safe, productive human space travel.