Medical researchers analyzed the possible effects of prolonged stays in space on astronauts. They concluded that although missions longer than 90 days do not directly affect the overall number of fractures caused by weakened bones, there is one exception that still raises concern.
Loss of Muscle and Bone Tissue in Microgravity
A new study has shown that the incidence of hip fractures among astronauts after spaceflights lasting more than 90 days was higher than after shorter journeys in microgravity or among people who had not been astronauts. The findings of the medical study highlight the need for an expanded assessment of astronauts’ long-term skeletal health. This was reported by phys.org.
The National Aeronautics and Space Administration (NASA) is planning a number of missions lasting more than six months in space, including commercial activities in low Earth orbit, the first crewed Artemis IV mission to the Moon’s south pole in 2028, as well as the creation of sustainable surface capabilities on our satellite in preparation for a flight to Mars. The growing number of people spending more time in extraterrestrial exploration environments may negatively affect the long-term skeletal health of astronauts selected according to physical fitness and optimal health criteria.
Loss of muscle mass and bone tissue caused by microgravity conditions in space is common among astronauts and indicates a risk of bone fragility as the body adapts to the absence of physical loading.
Dr. Jean D. Sibonga, principal investigator of the project “Increased Hip Fracture Incidence Associated with Long-Duration Spaceflight” at NASA’s Johnson Space Center, noted that people do not feel the effects of bone loss. After returning from space and feeling stable or recovered, astronauts may resume physically demanding activities despite hidden skeletal changes caused by prolonged inactivity. A better understanding of bone health after spaceflight may help astronauts, patients, and physicians assess long-term health concerns, determine appropriate care, and reduce the risk of injury.
Statistical Study of Hip Fracture Incidence Among Astronauts
Matthew T. Drake, M.D., Ph.D., of the Department of Endocrinology and Metabolic Bone Diseases at the Hospital for Special Surgery in New York, is a co-author of the accompanying editorial “Bone Loss in Astronauts.” He noted: “Although the data on spaceflight-associated bone loss are consistent to date, their main limitation is precision, because sample sizes are small and spaceflights are infrequent.”
To overcome this statistical limitation, the researchers surveyed a group of astronauts living in the United States about all fractures recorded during annual clinical examinations and analyzed the data using Bayesian probabilistic modeling. They found no increased incidence of all types of fractures, but the rate of hip fractures among astronauts was higher after spaceflights lasting more than 90 days.
Hip fractures occurred at a younger age than would be expected in the non-astronaut population, and their incidence was higher than before the start of a long-duration mission or among astronauts who had not participated in spaceflights.
The scientists note that the detection of hip fractures at an earlier-than-expected age after prolonged spaceflight is clinical evidence that bone loss may lead to real long-term consequences that should be addressed accordingly.
More Detailed Examinations to Develop Preventive Measures
Sibonga emphasized the need to expand NASA’s current bone-health monitoring program beyond measurements of bone mineral density using dual-energy X-ray absorptiometry in order to better assess astronauts’ long-term fracture risk. NASA has recently begun prescribing quantitative computed tomography examinations before and after stays in microgravity. These examinations can provide more detailed information about different regions of the bones and whether individuals have fully recovered after a flight. Without this information, astronauts may risk placing excessive stress on bones that have not yet returned to their preflight condition.
To reduce these risks, the researchers recommend taking preventive measures that will help preserve astronauts’ baseline skeletal health before flight. A more complete characterization of changes in bone mass, density, structure, and microarchitecture caused by spaceflight will help determine which measures — whether medication, exercise, or dietary adjustments — are most effective for the long-term skeletal health of people who travel in space.
