Lost in space: returned astronauts struggle to recover bone density, study finds

Lack of gravity and weightlessness means the longer astronauts stay in space, the more bone mass they lose

Astronauts lose decades' worth of bone mass in space that many do not recover even after a year back on Earth, researchers have found, warning that it could be a big concern" for future missions to Mars.

Previous research has shown astronauts lose between 1% and 2% of bone density for every month spent in space, as the lack of gravity takes pressure off their legs when it comes to standing and walking.