Oh, brother! NASA twins study shows how space changes the human body

FILE PHOTO: NASA astronaut Scott Kelly (R), member of the 43 International Space Station crew, and his twin brother Mark pose after a news conference at Baikonur cosmodrome March 26, 2015. REUTERS/Maxim Zmeyev/File Photo

COLORADO SPRINGS, Colo. (Reuters) - An American astronaut experienced multiple biological changes in space but returned to normal - with some exceptions - after coming back to Earth, according to a study involving twin brothers that shed light on how space flight affects the human body. 

In research published on Thursday, scientists compared Scott Kelly to identical twin Mark Kelly after Scott spent 340 days in orbit on the International Space Station and Mark remained Earth-bound. Both are now retired as NASA astronauts, and Mark is running for a U.S. Senate seat in Arizona.