Spinal bone mineral after 5 weeks of bed rest

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Abstract
Patients put at bedrest for medical reasons lose 1–2% of spinal bone mineral per week. Losses of this magnitude during even shortterm space flights of a few months would pose a serious limitation and require countermeasures. The spinal bone mineral (L2–L4) was determined in 6 healthy males (precision=2%) before and after 5 weeks of complete bed rest. Only one individual had a significant loss (3%) and the −0.9% mean change for the 6, was not significant (P=0.06). The average negative clacium balance during the 5 weeks was 4 g or 0.36% of total body calcium, similar to that reported in other bed-rest studies. Spinal bone loss, however, in healthy bed-rested males is significantly less than reported for bed-rested patients, suggesting that a large loss of spinal bone mineral does not occur during space flight missions lasting 5 weeks or less.