Spaceflight and calcium metabolism

Calcium metabolism data from spaceflight have been obtained primarily from Skylab astronauts, from Soviet Salyut-6 cosmonauts, and from growing rats flown either on the Soviet Cosmos series or Spacelab 3. In this report, the results from Skylab astronauts will be compared to data from bed rested subjects, and the results from Cosmos rats will be compared to data from a ground-based rat model, to help explain (1) how spaceflight or gravitational unloading alters calcium metabolism in adult humans and growing rats, (2) the relevance of the observations of bone dynamics in growing rats to the changes in adult man, and (3) the sequence of events leading to changes in calcium metabolism during spaceflight. A hypothetical scheme of the mechanisms causing altered bone mass during spaceflight will be proposed.