The two major problems with extended space travel are the effects of radiation and low gravity on the human body. This is what a current NASA employee, former air force colonel told me. That is also why astronauts do not stay on the International Space station for more than a year. They all come back shorter and near sited among other problems.
They all come back shorter and near sited among other problems.
Don’t know about the near-sightedness, but they come back taller, not shorter. The lower, or lack of, gravity causes the spinal column to decompress, making them taller, at least temporary.
Even Howard was taller when he came back.