The results were published on April 11th, in Science in a paper titled, "The NASA Twins Study: a multidimensional analysis of a year-long human spaceflight".
Mr. Scott, 50, spent 340 consecutive days on the ISS - from March 27, 2015 to March 1, 2016.
"The "Twins Study" has been an important step toward understanding epigenetics and gene expression in human spaceflight", said J.D. Polk, chief Health and Medical Officer at NASA Headquarters, in a statement. The astronaut was supposed to spend a year on the ISS, and the space agency would compare his development to his twin brother on Earth. Gene expression data corroborated and supported other findings in the Twins Study, including the body's response to DNA damage, telomere regulation, bone formation and immune system stress.
Persistent changes were observed in a few other areas, including some cognitive function. Numerous findings are consistent with data collected in previous studies, and other research in progress.
The findings showed that the telomeres in Scott's white blood cells, which are biomarkers of ageing at the end of chromosomes, were unexpectedly longer in space then shorter after his return to Earth with average telomere length returning to normal six months later.
"Our main findings in Mr. Scott were that the carotid artery wall became thicker early in flight and remained so throughout the mission", Dr. Stuart Lee of NASA's Johnson Space Center said.
Further, Scott's immune system responded appropriately in space.
A flu vaccine administered in space worked exactly as it would on Earth, indicating that the immune system is not significantly compromised outside the planet.
The scientists also found that the astronaut's telomeres - the protective caps on the ends of chromosomes - got longer while he was in space. These findings help demonstrate how a human body was able to adapt to the extreme environment of space and help researchers better understand how environmental stressors influence the activity of different genes, leading to a better understanding of physiological processes in space.
For example, Scott experienced a large-scale shift in the way his genes expressed themselves while he was in space, but it didn't seem to affect his health and largely went back to normal upon his return, researchers said. It also showed that only a small percentage of gene expression did not return to baseline. But the report shows anew that the human body is adapted for life on the surface of Earth and goes haywire in zero gravity.
Ten teams of specialist scientists from all over the USA were involved in researching the physiological, molecular, and cognitive changes that occurred in Scott after his year on the International Space Station (ISS) - while his brother remained firmly on Earth. Researchers also found that changes in Scott's diversity of gut flora in space were no greater than stress-related changes scientists observe here.
The Twins Study helped establish a framework of collaborative research that serves as a model for future biomedical research. Principal investigators at NASA and at research universities across the nation initiated an unprecedented sharing of data and discovery.
The study includes the work of 84 scientists comprising 10 teams from 12 universities. While significant, it is hard to draw conclusions for all humans or future astronauts from a single test subject in the spaceflight environment.