Although you lose bone density (and continue to when you return).
bone density is overrated
I am reading the book he wrote on his 1-year in space, very good and not too technical. It was distressing to read the pain he was in when he returned on earth, couldn’t sleep or be in bed. A lot of changes happen in their bodies, in my opinion they are very courageous going knowing how they will be affected, true pioneers. Wish both brothers the best, even if I don’t agree with their politics.