Dual-energy x-ray absorptiometry (DEXA) scans have shown how in-flight exercise regimens can help maintain bone microarchitecture in astronauts on long space missions, according to NASA scientists.
The finding is from an analysis of DEXA scans of 51 astronauts before and after spaceflights aboard the International Space Station (ISS), noted corresponding author Jean Sibonga, PhD, of the NASA Johnson Space Center in Houston, TX, and colleagues.
“DEXA can detect how various in-flight countermeasures and the length of mission affect the lumbar spine that is enhanced with the addition of [trabecular bone score],” the group wrote. The study was published January 13 in Archives of Osteoporosis.
Preflight and postflight DEXA measurements of bone mineral density (BMD) are required for all long-duration astronauts to describe the effects of prolonged space exposures, the mitigation of effects by spaceflight countermeasures, and the recovery to preflight status after return to Earth, the authors explained. Trabecular bone score (TBS) is an additional measurement on DEXA scans that can specifically assess bone microarchitecture.
In this study, the researchers hypothesized that TBS could be a useful addition to BMD in astronaut skeletal health assessments. The group first calculated BMD and TBS measurements from DEXA scans from 51 crewmembers: 41 men (age range, 37 to 56) and 10 women (age range, 41 to 50) who flew on six-month missions.
For the analysis, they categorized participants into three groups based on their access and use of an advanced resistive exercise device (ARED), an ISS exercise hardware that simulates lifting weights in the microgravity of space, with or without the use of drugs to prevent and treat osteoporosis (bisphosphonates).
According to the results, postflight lumbar spine BMD was significantly lower than preflight lumbar spine BMD (−4.4%, p < 0.001) in the group (n = 24) whose spaceflights predated the availability of the ARED on the space station, but not in the group with access to the ARED (n = 20: −1.9%, p < 0.01) or in the group with access to the ARED and who were taking bisphosphonates (n = 7: + 2.8%, p = 0.1).
Similarly, for TBS, a decline from preflight was statistically significant in the group without access to the ARED (−3%, p < 0.01) but was not statistically different from preflight in both the ARED group (+ 0.2%, p = 0.7) and the ARED plus bisphosphonates group (−1.5%, p = 0.3), the researchers reported.
“This is the first report of TBS to evaluate the effects of spaceflight on the integrity of trabecular bone in the lumbar spine of astronauts,” the group wrote.
Ultimately, with multiple missions beyond six months planned before the decommissioning of the ISS in 2030 and longer stays on the Moon and Mars projected, safeguarding astronaut skeletal health has become even more important, the researchers noted.
“Based on our current findings, we recommend integrating TBS into normal monitoring procedures at NASA Johnson Space Center as a method of acquiring additional information on the bone health of astronauts without additional radiation exposure,” the group concluded.
The full study is available here.
