Calcium metabolism in space flight

Immobilization has been shown repeatedly to induce a loss of skeletal substance accompanied by hypercalcemia and hypercalcuria. Older data from paraplegics, polio patients, fracture patients and immobilized normal volunteers are reviewed. More recent studies of bone densitometry on normal volunteers and astronauts of Gemini flights IV, V, and VII are reported briefly. Finally, metabolic balance studies from Gemini VII are summarized. The balance data suggest that adequate calcium intake and programmed exercise may control the problem of calcium mobilization. However, there are disquieting discrepancies between the densitometric results (which show bone losses) and the balance data (which show no bone loss). Either the densitometric results are in error or there occur alarming intraskeletal transfers of bone mineral not detected by the balance approach.