Spaceflight osteoporosis: current state and future perspective.

Osteoporosis is one of the established major consequences of long-duration spaceflights in astronauts seriously undermining their health after their returning on Earth. Indeed, astronauts typically lose more bone mass during one month than postmenopausal women on Earth lose in one year. To date, countermeasures mainly consist in exercise and supplementation while pharmacological treatment as those used in postmenopausal women are not routine. However, it is evident that exercise and supplementation alone are not enough to maintain bone homeostasis. In this paper we describe the current countermeasures for bone loss during long-term spaceflight, review the modern treatment which are successfully employed to prevent osteoporosis on Earth and that could be quickly used also for astronauts and finally focus on the recent cellular and molecular understanding of bone homeostasis which might provide the basis for the development of future targeted therapies.