Space travel may harm astronauts' joints: Study

Space travel can be detrimental to the joints of astronauts, say scientists who have found early signs of cartilage breakdown in mice sent aboard a Russian spaceflight.

The study adds to a growing body of research about the health effects of spaceflight on the musculoskeletal system, according to the researchers from Henry Ford Hospital in the US.

Research has shown that living and working in space leads to many changes in the human body including the immune system, blood pressure and the shape of a person's eyes.

"We believe this degradation is due to joint unloading caused by the near lack of gravity in space. If this were to happen to humans, given enough time, it would lead to major joint problems," Jamie Fitzgerald, from Henry Ford Hospital.

Researchers theorise that because the biomechanical forces in space are different from those on Earth, changes to the musculoskeletal system occur.

"We do know that tissues of the musculoskeletal system - bone, muscle, tendon, cartilage and ligament - are constantly subjected to 'loading' everywhere on Earth," Fitzgerald said in a statement.

"This comes from daily activities like walking and lifting, and the action of gravity pulling down on the musculoskeletal system," Fitzgerald said.

"When that loading is removed due to weightlessness and near-zero gravity in space, these tissues begin to degrade. The most dramatic example is the atrophy of muscle and demineralisation of bones that occurs during spaceflight," he said.

"This muscle and bone loss are reversed when the astronauts return to Earth. What is interesting about cartilage is that it's a tissue that repairs very poorly. This raises the important question of whether cartilage also degrades in space," he added.

For the study, the researchers analysed the molecular changes in the cartilage of mice that spent 30 days in animal research enclosures aboard an unmanned Russian Bion-M1 spacecraft in 2013.

This included performing tissue stains and gene expression studies on the cartilage. The results were compared to mice observed on Earth during the same period.

"Overall, we can say that after 30 days of microgravity, the process of cartilage-degrading began. We saw changes in the gene expressions that were consistent with cartilage breakdown," Fitzgerald said.

Video footage taken of the mice showed them floating around in their enclosure during the day. At night, the footage showed them struggling to climb over each and hang onto the grate inside the enclosure.

In comparison, the mice on Earth showed no discernible cartilage degradation.

More research is needed to develop a better understanding of what happens to the human body in space -- especially with a potential trip to Mars in the future.

"Because cartilage in humans doesn't readily repair, the return to Earth could potentially bring long-term health problems," said Fitzgerald.