The United States has done experiments related to human genetic variation caused by space environment. They chose a pair of identical twin brothers, let the younger brother go to the International Space Station, and the older brother stayed on the earth to observe. My brother came back after a year in space. By comparing with his brother, scientists found that his appearance and height are very different from his brother's, and about 7% of his DNA has changed.
However, it is worth mentioning that these changed DNA are only changes in activity, so strictly speaking, they are not mutations. Nevertheless, it cannot be said that going into space has no negative impact on people's health.
Astronauts will eventually return to earth. Adapting to the space environment and suddenly coming to the earth is actually a test of human health. First of all, it doesn't adapt to gravity. There is no gravity in space, and the astronauts' physical and mental state has adapted. When they suddenly return to earth, people will feel carsick. Stepping on the ground is like stepping on cotton. They can't even stand up, but this uncomfortable feeling can be gradually eliminated with time.
Another is the change of muscles and bones. Due to the low gravity environment in space, the density and strength of human bones will decrease, including the heart. Therefore, in order to return to the earth and restore normal muscle strength and bone density, astronauts must receive a series of careful treatments.
However, astronauts have spacesuits worth millions of dollars to resist space radiation, so they want to be affected by radiation. However, in order to minimize the influence of possible genetic variation, astronauts in various countries generally require to be married and have children when selecting female astronauts.