Bone marrow suffers almost no damage after a month in space
The experiments were performed on adult males of black laboratory mice. The mice spent a month in space on a satellite designated BION-M No. 1 («БИОН-М № 1» in Russian), from April 19 to May 19, 2013. After the landing the red bone marrow of the mice was examined and compared with the bone marrow of mice that remained on Earth during all this time.
The comparison showed that after a month in microgravity the number of stem cells in the red bone marrow decreases, but the effect wears off in just seven days in ordinary conditions on Earth.