The effects of microgravity on the skeletal system--a review.

Exposure of astronauts to microgravity leads to the loss of calcium from weightbearing bones. Prolonged exposure, e.g., during a journey to Mars, may present problems on return to Earth, with increased risk of fractures and premature osteoporosis in later life. The precise mechanisms of calcium loss have yet to be determined although a key feature is the absence of mechanical loading. Countermeasures aimed at reducing calcium loss to acceptable levels include the use of exercise, drugs, dietary modifications and inertia suits such as the Soviet "Penguin" suit. Missions of a number of years may, however, require the development of artificial gravity on a spacecraft. The country that first solves the physiological problems of man in space and, in particular, skeletal calcium loss, will almost certainly be the first to be able to put a man on Mars.