A new study has shed light into the long-term effects of spending an extended period of time in space on the human body, revealing that the human heart physically shrinks.Conducted by scientists at the University of Texas Southwestern Medical Center, the research was done in anticipation of NASA's preparations to send humans to Mars within the next decade, a press release announced on Monday.Basing their study on retired astronaut Scott Kelly, who spent almost a year on the International Space Station (ISS), the scientists found that his heart shrank by a minute degree despite a strict exercise regimen. However, in terms of functionality, the researchers found that his heart continued to work normally. Published in the academic journal Circulation, the results indicate that Kelly lost around 0.74 grams in his heart's mass per each week spent on the ISS, which was deemed equivalent to similar effects on a long-distance swimmer having spent half a year attempting to cross the Pacific Ocean.Prof. Benjamin Levine, the central author of the study, said that Kelly's heart still adapted well to the new zero-gravity environment. Levine is a professor of internal medicine at UT Southwestern, and is also the director of the Institute for Exercise and Environmental Medicine (IEEM) at Texas Health Presbyterian Hospital Dallas.“It did shrink a little bit. It did atrophy and it did get a little smaller, but the function remained good,” Levine said in a press release from the University of Texas Southwestern Medical Center. “I think this is encouraging for long-duration space flight. It shows that even after a year in space, the heart adapts relatively well.”Expanding the sample size of the study, Levine has also been conducting research on 13 astronauts who were in space for at least six months. Those results showed that the heart's adjustment to zero-gravity is dependent on the astronaut, with most, though not all, losing muscle mass in space. The reason for this, according to Levine, is that “It all depended on how much work the astronaut’s heart did in space relative to how much it regularly did on the ground.”For his work on the impact of space travel on humans, NASA gave Levine some $3.8 million in funding to focus on other bodily areas impacted by zero-gravity.The rationale for its comparison to elite swimmers in the new study is based on the idea of putting the human body into similar weightless conditions, Levine noted.Beyond his role in helping NASA, Levine has conducted studies on the impact of endurance swimming on the human heart, which shares the similarity of a loss of muscle mass seen in astronauts, particularly in the left ventricle.Besides the lead author, UT Southwestern researchers James MacNamara, Katrin Dias and Satyam Sarma also contributed to the study, as well as Stuart Lee and David Martin of Wyle Science, Technology, and Engineering Group, along with Maks Romeijn of Critical Care International.