"Most of what we have learned about living in space is that we should not live in space. We are designed for gravity; without it, strange things happen to both body and mind. For each month spent in space, humans can lose up to two per cent of their bone mass. This means that each day, for hours on end, the ISS becomes the world’s highest-flying gym to keep its occupants fit. But even with such precautions, some returning space travellers require months of rehabilitation to readjust to life on Earth. Others, despite having access to the best facilities and treatments available, experience headaches, sight loss, and undiagnosed physical and psychological frailty for the rest of their lives."
"Most of what we have learned about living in space is that we should not live in space. We are designed for gravity; without it, strange things happen to both body and mind. For each month spent in space, humans can lose up to two per cent of their bone mass. This means that each day, for hours on end, the ISS becomes the world’s highest-flying gym to keep its occupants fit. But even with such precautions, some returning space travellers require months of rehabilitation to readjust to life on Earth. Others, despite having access to the best facilities and treatments available, experience headaches, sight loss, and undiagnosed physical and psychological frailty for the rest of their lives."
http://www.aeonmagazine.com/nature-and-cosmos/greg-klerkx-sp...