A new study suggests that staying for long time in space do not affect astronauts health. This was the result of a study that compared Scott Kelly to identical twin Mark Kelly after Scott spent a year on the International Space Station and Mark remained Earth-bound. According to NASA, most of the biological changes that appeared in space, including some subtle differences in the genetic activity, were gone after the conclusion of the mission. The study findings were published in the latest issue of the journal Science, the German News Agency reported. Scott Kelly spent around a year on the International Space Station, from March 2015 till February 2016, and then he retired, but still working in the researches related to his mission. In this study, the researchers aimed at investigating the impact of life in space on the human body, by comparing the similarities and differences between Scott, who stood for one year in space, and Mark who is few minutes older than his twin brother, retired as well, and remained on Earth. Scientists hope to use those information in future manned missions. This study was conducted by 10 teams including 80 researchers from 12 countries. This was the first space experiment involving twin astronauts. Although over 550 people went up to space, only eight astronauts stood more than 300 days. Scott remained in space for 340 days. The brothers Kelly are the only identical twin astronauts who visited outer space, and both underwent several tests before, during, and after the mission. In space, people are exposed to gravity loss and radiations, but science has not yet determined the impact of those factors on human health, or the changes that can occur while in space. Scott Kelly wrote in his book dubbed "Endurance, A Year in Space" published in German, that after he returned home, he felt like he was an old man, and suffered from severe aches in his swelling legs, sickness, and itchy skin.