Do you remember the news of the Russian cosmonaut who returned to Earth after having stayed in space for a year? He sat in a wheelchair, had a big smile on his face and waved to the news reporters. Why did he (and many other astronauts) have to sit in a wheelchair? The short answer is that he suffered bone mass loss and muscle degeneration in space. The bone mass loss is called osteoporosis.

NASA Studies Bone Mass Loss in Space

From the SLS-1 mission (Spacelab Life Sciences 1, 1991), NASA scientists reported that alterations in cell metabolism, immune cell function, cell division, and cell attachment have occurred in space.

Studies on rat bone cells revealed a significant number of floating, dead bone forming cells. Bone cells die if they are unsuccessful in attaching themselves to something. This finding could be significant since many biological processes, both in single cells and in multicelled organisms, depend on cell attachment and the recognition processes. The finding suggests that gravity clues may be required to show the cells where to attach themselves. Furthermore, studies of rat bone cells also revealed that healthy cells showed no signs of producing minerals. It may be that bone cells do not need to produce minerals to support themselves in a microgravity environment.

Similar studies of mouse bone cells developed in space and of those developed on the ground revealed similar changes in attachment properties in microgravity. Microscopic examination of the surfaces of flight cells revealed that they were smoother than cells used in the ground-based control experiment. This finding indicated that matrix production or secretion is altered in microgravity. Matrix forms the basic structure of bone.

To date, there is not yet an effective countermeasure to bone mass loss during spaceflight. The common solution implemented by NASA, the Russian Aviation and Space Agency, and the European Space Agency is to exercise during spaceflight. NASA uses a "treadmill" that allows astronauts to stimulate stress on bones in space. The old saying works, "no stimulation, no reaction".

Prior to spaceflight, astronauts take calcium supplements to increase the calcium content in their bones, an effort to reduce the rate of bone mass loss during spaceflight.