Researchers International Space Station (ISS)

Researchers already know that spending long periods of time in a zero-gravity —such as that inside the International Space Station (ISS) — results in loss of bone density and to the body’s muscles. That’s partly why stays aboard the ISS are at six months. And now, a number of NASA astronauts are reporting that their 2020 vision after spending time in space, with many needing glasses once they returned to Earth.