Spaceflight does only affect the astronauts mentally; it also causes modifications in their bodies and these implications are not just skin deep, rather it goes onto affect the genes of the astronauts in space. Space travel strongly influences the way genes are expressed or turned on and off, reveals the preliminary results of NASA's "Twins Study."

"Some of the most exciting things that we've seen from looking at gene expression in space is that we really see an explosion, like fireworks taking off, as soon as the human body gets into space," said the study's principal investigator Chris Mason, who's based at Weill Cornell Medicine, Cornell University's medical school. "With this study, we've seen thousands and thousands of genes change how they are turned on and turned off. This happens as soon as an astronaut gets into space, and some of the activity persists temporarily upon return to Earth," Mason added in his statement.

To be more specific, Mason and his team observed an increase in methylation, which involves slapping methyl groups onto stretches of DNA. This process usually slows down the activation of the genes involved.

The Twins Study has been conducted on former NASA astronauts Scott and Mark Kelly, who are identical twins and, therefore, share a single DNA profile.

Scott Kelly and cosmonaut Mikhail Kornienko were stationed at the International Space Station (ISS) during March 2015-March 2016. They completed an unprecedented 11-month mission. On the other hand, Mark Kelly stayed on Earth this entire time, serving as a control against which to measure the changes that spaceflight may have induced in Scott.

The study is still incomplete and the researchers are still assessing the changes, through 10 separate investigations that constitute the broader Twins Study. As per one NASA official, the final results should be out by next year, reported the Scientific American.

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"This study represents one of the most comprehensive views of human biology. It really sets the bedrock for understanding molecular risks for space travel as well as ways to potentially protect and fix those genetic changes," Mason said.

Other than that, a tour to space also induces change to the astronauts' bodies on a macro level, which include muscle atrophy, decreased bone density and visual deterioration. However, these effects have been long known by the scientists and astronauts do take precautions to mitigate some of them before their flights.