Recovery of spaceflight-induced bone loss: Bone mineral density after long-duration missions as fitted with an exponential function

NASA, Вашингтон, West Virginia, United States
Bone (Impact Factor: 3.97). 01/2008; 41(6):973-8. DOI: 10.1016/j.bone.2007.08.022
Source: PubMed


The loss of bone mineral in NASA astronauts during spaceflight has been investigated throughout the more than 40 years of space travel. Consequently, it is a medical requirement at NASA Johnson Space Center (JSC) that changes in bone mass be monitored in crew members by measuring bone mineral density (BMD), with dual-energy X-ray absorptiometry (DXA) before and after flight, of astronauts who serve on long-duration missions (4-6 months). We evaluated this repository of medical data to track whether there is recovery of bone mineral that was lost during spaceflight. Our analysis was supplemented by BMD data from cosmonauts (by convention, a space traveler formally employed by the Russia Aviation and Space Agency or by the previous Soviet Union) who had also flown on long-duration missions. Data from a total of 45 individual crew members - a small number of whom flew on more than one mission - were used in this analysis. Changes in BMD (between 56 different sets of pre- and postflight measurements) were plotted as a function of time (days after landing). Plotted BMD changes were fitted to an exponential mathematical function that estimated: (i) BMD change on landing day (day 0) and (ii) the number of days after landing when 50% of the lost bone would be recovered ("50% recovery time") in the lumbar spine, trochanter, pelvis, femoral neck and calcaneus. In sum, averaged losses of bone mineral after long-duration spaceflight ranged between 2% and 9% across all sites with our recovery model predicting a 50% restoration of bone loss for all sites to be within 9 months.

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    • "Peripheral quantitative computed tomography (CT) analysis of distal tibia in astronauts aft er six months of spacefl ights showed up to 24% of trabecular bone lost and aft er six months from the return on Earth the recovery of bone mineral density (BMD) was not complete (Vico et al. 2000). Indeed, the recovery of skeletal density aft er long-duration space missions was estimated to exceed one year (Sibonga et al. 2007). Th ese data have suggested that i) mechanical stress, as that induced by Earth's gravity, was a crucial underlying factor for normal bone homeostasis; ii) exposure to weightlessness was a causal factor of osteoporosis; iii) the loss of bone mass was more quick in astronauts than postmenopausal women; and iv) the severity of osteoporosis was proportional to the length of exposure to microgravity (Vogel 1975; Hughes-Fulford 2011). "
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    • "As previously described (Smith et al. 2005b, 2008; Sibonga et al. 2007), areal bone mineral density (BMD) scans for both the UCSD and UTMB bed rest studies were performed by dual-energy X-ray absorptiometry (DXA) using either a Hologic QDR 450 or Hologic Discovery instrument (Hologic, Bedford, MA) at UTMB (Spector et al. 2009), or a Hologic Delphi W or Lunar DPX-IQ instrument at UCSD (Zwart et al. 2007). Scans were performed 8–13 days before bed rest and again 1–2 days after bed rest, only on the subjects who participated in the 30-day study at UCSD and the 60- and 90-day studies at UTMB. "
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