Femur bone density loss in mice aboard the ISS sheds light on space travel challenges
by Bob Yirka, Phys.org
A team of biomedical engineers at the Blue Marble Space Institute of Science, in collaboration with bio-scientists from NASA Ames Research Center, have discovered that test mice living aboard the International Space Station (ISS) experience substantial femur bone density loss when compared to control mice residing on Earth.
In their study published in the open-access journal PLOS ONE, the combined team found that after a month in orbit, these mice exhibited notable differences in bone mass and density.
Previous research has established that human astronauts tend to lose approximately 1% of their bone density each month while aboard the ISS. This alarming trend suggests that during extended missions, such as multi-month excursions, astronauts may end up experiencing the equivalent of decades' worth of bone loss within a few months. While exercise has proven to mitigate some of the adverse effects, it still fails to eliminate the problem entirely.
In the current study, the researchers focused on the effects of microgravity on rodents—specifically, how freefall affects animals that travel on four legs, as opposed to the two-legged human astronauts.
Since humans walk upright, the impact of gravity primarily exerts pressure on the spine, hips, and legs. In contrast, four-legged animals bear significant weight pressure through their limbs. This study aims to determine whether bone loss can be solely attributed to reduced gravity or if additional factors, such as exposure to space radiation, require consideration.
Upon examining the test mice who spent 37 days in space, the research team noted that the most pronounced bone loss occurred in the femurs—the skeletal components responsible for bearing a significant portion of their body weight. Notably, denser bone tissue at the hip joint, which connects above the femur, saw minimal bone loss, which strongly suggests that the diminished gravitational pull primarily affected the femurs.
Furthermore, the research team posits that altering astronauts' diets or enhancing shielding against space radiation may not resolve bone loss. Instead, it appears that alternative approaches are critical for ensuring astronaut health during long-term space missions, such as potential journeys to Mars.
More information: Rukmani Cahill et al, 37-Day microgravity exposure in 16-Week female C57BL/6J mice is associated with bone loss specific to weight-bearing skeletal sites, PLOS ONE (2025). DOI: 10.1371/journal.pone.0317307
Journal information: PLoS ONE
Femur bone density loss in mice aboard the ISS sheds light on space travel challenges
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