[Bone loss and bone metabolism in astronauts during long-duration space flight]

Significant bone loss is one of the most serious medical concerns during long-duration space flight. This article provides the results of bone loss and bone metabolism obtained from American and Russian long-duration human space flight. Bone loss in astronauts before and after long-duration space flight was evaluated by dual energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT). DXA revealed bone loss at rates of 0.9%/month in the lumbar spine and 1.5%/month in the femoral neck. QCT revealed cortical, trabecular and integral BMD in the femoral neck at rates of 0.5%/month, 2.5%/month, and 1.5%/month, respectively. Biochemical markers of bone resorption increased during space flight and several months after landing. Bone formation marker was unchanged during space flight, but since 3 weeks after landing it was significantly higher than before flight. A calcium kinetics study confirmed that bone resorption increased, and intestinal calcium absorption decreased during space flight.