Scientists from the University of Calgary and elsewhere followed 17 astronauts on the International Space Station before and after spaceflight over the past seven years to find out if bones regenerated after a “long” spaceflight. Their results show that while bone is partially restored after flight, the long-term losses represent at least a decade of normal age-related bone loss, potentially advancing the onset of osteoporosis.
Gabel et al. investigated bone strength, density, and microarchitecture in seventeen astronauts using high-resolution peripheral quantitative computed tomography. Image credit: NASA.
“The deleterious effect of spaceflight on skeletal tissue can be profound,” senior author Dr. Stephen Boyd of the University of Calgary and colleagues wrote in their paper.
“Decreased mechanical loading in microgravity causes significant loss of bone mineral density and strength and deterioration of trabecular microarchitecture.”
“Biochemical studies of bone turnover highlight altered bone metabolism during spaceflight, such that biomarkers of bone resorption increase during spaceflight while biomarkers of bone formation lag, resulting in net bone loss.”
“Restoring bone mineral density and strength upon return to Earth’s gravity is a long process, and many astronauts’ bones never fully recover,” they added.
“Determining who is most at risk of incomplete bone repair is important to understanding the feasibility of missions beyond low Earth orbit.”
“The primary goal of our study was to use high-resolution peripheral quantitative computed tomography to investigate the recovery of bone microarchitecture, density, and strength after long-duration spaceflight.”
The prospective study included 17 astronauts (14 men and 3 women; mean age – 47 years; height – 177.7 cm; body mass – 79.1 kg) from NASA, the Canadian Space Agency (CSA), the European Space Agency (ESA) and Japan Aerospace Exploration Agency (JAXA) that were selected for missions to the International Space Station (ISS).
The authors photographed the participants before spaceflight, upon return to Earth, and after six and 12 months of recovery.
They carried out bone scans of the tibia (shin) and radius (forearm) to calculate the bone’s resistance to fracture (breaking load), bone mineral in bone tissue and tissue thickness.
They also recorded exercises such as cycling, treadmill running and deadlifts performed by astronauts during and after flight.
One year after the flight, mean scores for 16 of the astronauts showed incomplete tibial recovery.
The average tibial load, a measure of bone strength, was reduced by 152.0 newtons (N) from 10,579 N before the flight to 10,427 N after one year.
Total bone mineral density was reduced by 4.5 mg/cm3 compared to pre-flight levels of 326.8 mg/cm3.
Forearm measurements in all astronauts were no different at 12 months recovery compared to preflight.
The researchers noted that astronauts on missions longer than six months (a total of eight astronauts) had significantly less bone recovery.
In astronauts on missions longer than six months, the mean tibia load at failure decreased by 333.9 N after one year compared to before flight, while in astronauts on missions shorter than six months (nine astronauts), the failure load decreased by 79 .9N.
Similar differences were found for total bone mineral density in the tibia.
A total of nine of the astronauts (seven from long missions) had not fully recovered total tibial bone density after 12 months.
Across all astronauts, those who completed a greater amount of in-flight deadlift training compared to their individual pre-flight training were identified as having a proportion of those who recovered tibial bone mineral density.
“Like currently used exercise routines, resistance-based jumping exercise that provides high-impact dynamic loading of the legs may help prevent bone loss and promote bone formation during spaceflight,” the researchers said. .
Their article was published on June 30, 2022 in the journal Scientific Reports.
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L. Gabel and others. 2022. Incomplete recovery of bone strength and trabecular microarchitecture in the distal tibia 1 year after return from long-duration spaceflight. Sci Rep 12, 9446; doi: 10.1038/s41598-022-13461-1
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