NASA

Spending several months in space -- as astronauts do aboard the ISS -- would be, well, pretty amazing. But there's a huge trade-off: humans evolved on Earth, with Earth's gravity. Our bodies are suited to those conditions, and floating weightlessly for extended periods has some not-inconsequential health implications.

The biggest, perhaps, of these is the loss of bone and muscle density. Even when you don't think you're doing anything, the human body is constantly working against the Earth's gravitational pull. When you enter Zero-G, though, those muscles no longer have to work -- and your bones, which constantly remodel in response to mechanical stress -- no longer need to shore up against gravity either.

This results in rather rapid loss of mass -- about 1 to 2 percent per month for bone mass and up to 20 percent in as little as 5 to 11 days for muscle without exercise. Even with exercise, astronauts in Zero-G lose bone and muscle mass.

Investigations by the Japanese Aerospace Exploration Agency aboard the ISS may help figure out how this deterioration occurs -- and what may be done to prevent it. The team will be studying the effects of microgravity on Caenorhabditis elegans -- a millimetre-long roundworm that is often used in research as a model for larger organisms.

The team will be conducting two different studies. The first, called Alterations of C. elegans muscle fibers by microgravity, taking place in early 2015 will monitor the worm's muscle fibres and cytoskeleton to observe how they change in response to Zero-G. The worms will be grown in two environments: microgravity, the natural gravity level on the ISS; and in a centrifuge that simulates One-G (the level of gravity on Earth). This will allow the researchers to compare the two to see the precise difference between the effect of Earth gravity and the effect of microgravity.

NASA

The Epigenetics in spaceflown C. Elegans study, already under way, is examining the DNA of the worms. The team is growing four generations of the worms in space, with adults and larvae of each generation preserved at different points in their lifespan. These will then be compared to similar batches of worms grown in a lab in Japan.

"The astronauts will cultivate multiple generations of the organism, so we can examine the organisms in different states of development," said Atsushi Higashitani, of Tohoku University in Miyagi, Japan, principal investigator for both investigations.

"Our studies will help clarify how and why these changes to health take place in microgravity and determine if the adaptations to space are transmitted from one cell generation to another without changing the basic DNA of an organism. Then, we can investigate if those effects could be treated with different medicines or therapies."

Both studies could also help patients on Earth, too. The loss of bone density experienced by astronauts is similar to the characteristics of osteoporosis, while loss of muscle is also experienced by paralysis patients and others who are bedridden.

"Spaceflight-induced health changes, such as decreases in muscle and bone mass, are a major challenge facing our astronauts," said Julie Robinson, NASA's Chief Scientist for the International Space Station Program Office. "We investigate solutions on the station not only to keep astronauts healthy as the agency considers longer space exploration missions, but also to help those on Earth who have limited activity as a result of aging or illness."