NASA has uncovered alarming new insights into how prolonged weightlessness in space affects bone density, as female mice were sent aboard the International Space Station (ISS) for an unprecedented 37-day study. With a significant loss of bone density anticipated for astronauts—estimated to drop at least 1 percent for every month spent in space—this research is crucial for informing healthier, longer missions beyond Earth.

During the experiment, scientists closely monitored the growth and health of bones in mice living in microgravity conditions. These space-bound mice were compared to control groups on Earth, which included both standard vivarium environments and simulated conditions mimicking those on the ISS.

The findings revealed that bone loss is not the same across all skeletal sites. Specifically, weight-bearing bones, such as the femurs, experienced more significant loss compared to non-weight-bearing bones like the spine. This suggests that microgravity uniquely affects how bones react to stress, rather than radiation exposure, which has been previously speculated.

Interestingly, the study’s results echo prior investigations involving medaka fish also aboard the ISS, which indicated that microgravity disrupts the delicate balance between bone-forming cells called osteoblasts and bone-resorbing cells known as osteoclasts. In zero-gravity, osteoclasts seemed to be excessively active, leading to a reduction in bone mineral density.

However, the new research indicates that not all bones suffer equally. While weight-loaded bones like the femur lose significant mass, some bones retain their density or even become denser. This anomaly may be linked to increased blood pressure in astronauts’ upper bodies during the initial days in orbit, resulting in facial swelling, headaches, and altered senses. Fortunately, these effects typically diminish as the body adjusts to the absence of gravity.

These revelations present significant implications for future long-duration space missions, including eventual trips to Mars and beyond. Understanding the mechanisms behind bone loss could pave the way for innovative treatments to counteract these effects, ensuring that astronauts remain healthy and functional during extended periods away from Earth.