Femur bone density loss in mice aboard the ISS sheds light on space travel challenges
A team of biomedical engineers at the Blue Marble Space Institute of Science working with a team of bio-scientist colleagues from NASA Ames Research Center, both in the U.S., has found that test mice living aboard the International Space Station (ISS) experience a significant amount of bone loss in their femurs compared to control mice on Earth.
In their study in the open-access journal PLOS ONE, the combined team found differences in bone mass and density in test mice sent into orbit for a little over a month.
Prior research has shown that human astronauts experience loss of bone mass and density while aboard the ISS. On average, they lose 1% of their bone density each month, which means they can experience the equivalent of decades' worth of bone loss during a multi-month mission. Prior research has also shown that exercise can alleviate the problem, but cannot solve it altogether.
For this new study, the researchers looked at the impacts on mice sent to space to learn more about how freefall impacts creatures that walk on four legs instead of two.
Because humans walk on two legs, much of the impact of gravity falls to their spines, hips and legs. That differs from four-legged creatures—for them, gravity places the burden of their weight on the hips and legs. The idea behind comparing the two types of creatures is to find out if bone loss is due to nothing more than greatly reduced gravity, or if other factors are involved, such as space radiation.
In studying the test mice who were sent into space for 37 days, the research team found that most of their bone loss occurred in their femurs, the part of their skeleton that bears the brunt of their weight. They also noted that denser bone that formed the hip joint, above the femur, experienced very little bone loss, strongly suggesting that the bone loss in the femur was most likely due to the sudden change in gravitational pull.
The research team suggests that changing the diet of astronauts or offering them more shielding from space radiation may not reduce bone loss; thus, other methods are required if astronauts are ever to travel long distances in space, such as 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).
Journal information: PLoS ONE
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