Astronauts who spent more than 90 days in space had a higher rate of hip fractures after returning to Earth than astronauts with shorter missions, according to a study published October 1 in Mayo Clinic Proceedings. Researchers at NASA's Johnson Space Center examined fracture records from US astronauts. The finding is an association, and the small astronaut population limits how precisely the risk can be measured.
Extended exposure to microgravity reduces the load on bones and muscles. Scientists have long documented bone loss during spaceflight, but fewer data show whether that loss leads to fractures years later. The new analysis focuses on what happened during periods after long missions, as NASA and commercial operators prepare for more prolonged trips beyond Earth.
The team reviewed fractures reported during astronauts' annual clinical examinations. It compared periods before any spaceflight, after missions shorter than 90 days, and after at least one mission longer than 90 days. Researchers used Bayesian statistical modeling to account for the limited number of astronauts and the different lengths of follow-up. They found no higher rate for fractures overall, but the rate of hip fractures was higher after long missions.
The study also reports that those hip fractures occurred at younger ages than expected in the general population. Its authors say the pattern warrants closer study of long-term skeletal health. An accompanying editorial cautions that small cohorts and rare flights make estimates uncertain. The results therefore cannot establish that a particular flight caused an individual fracture or determine how large the risk would be on future missions.
According to the researchers, a standard bone-density scan may miss changes in bone structure relevant to fracture risk. NASA has begun using more detailed computed tomography scans before and after flights, the study announcement says. Investigators propose examining bone mass, density and internal structure together to identify when astronauts have recovered sufficiently for demanding activity.
The team calls for further surveillance and research into protective measures, including exercise, diet and medicines, before longer lunar and eventual Mars missions. No specific treatment was shown by this study to prevent hip fractures. Its immediate implication is a need to track bone health after astronauts return, as well as during their time in space.
Comments