A NASA experiment shows that weightlessness selectively affects bones. The results could change how astronaut health is protected.
Mice sent to the International Space Station for 37 days experienced alarming bone loss. Contrary to common belief, this phenomenon does not uniformly affect their skeletons but specifically targets bones typically stressed by gravity.
Bones that "disappear"... but not all of them
The femurs of the mice, subjected to mechanical stress on Earth, lost up to 30% of their density. In contrast, their lumbar vertebrae, less dependent on gravity, remained stable. This divergence confirms that the absence of physical pressure primarily explains the deterioration.
Young mice also showed premature aging of their growth cartilage. Their ossification accelerated, a mechanism that could compromise bone development in future adolescent astronauts.
Finally, active rodents—thanks to cages with 3D walls—fared better. Their physical activity partially offset the effects of microgravity, offering a lead for crewed missions.
A critical challenge for space exploration
Astronauts lose up to 10% of their bone mass in six months, a rate ten times faster than terrestrial osteoporosis. Fractures could become a major risk during extended missions, such as a trip to Mars.
The study dismisses the space radiation hypothesis: non-weight-bearing bones, like vertebrae, are spared. Only weightlessness appears responsible, steering solutions toward targeted exercises or habitats simulating mechanical stress.
These findings highlight the urgency of adapting space technologies. Exoskeletons or artificial vibrations could become essential to preserving crew health.
Going further: Can bone loss after spaceflight be reversed?
Current data show that post-mission bone recovery is slow and often incomplete. After six months in orbit, an astronaut may take 3 to 5 years to regain their initial bone density, with significant variations among individuals. Some never fully recover, retaining effects comparable to early osteoporosis.
Rehabilitation protocols combine several approaches. Intensive physical exercise with heavy loads remains the most effective method, supplemented by nutritional supplements (vitamin D, calcium). NASA is also testing vibratory therapies and anti-osteoporosis drugs, with promising but still limited results.
A key factor appears to be mission duration. Beyond a year in space, bone damage could become irreversible. This is why researchers are studying preventive countermeasures: artificial gravity suits, advanced resistance exercise systems, and even early drug treatment.
These discoveries have significant terrestrial implications. They improve understanding and treatment of senile osteoporosis or that of bedridden patients. Space thus serves as an extreme laboratory for bone medicine, revealing mechanisms that would take decades to appear on Earth.
Article author: Cédric DEPOND