Essential Science: Why strong bones are needed for space travel

Posted Feb 1, 2016 by Tim Sandle
One limitation with a deep space mission, such as to Mars, is the effect of microgravity on astronauts. To find ways to build-up resilience and maintain bone strength, scientists have, surprisingly, been studying fish.
An astronaut takes a  selfie  in space. Oxford Dictionaries  word of 2013 was  selfie
An astronaut takes a "selfie" in space. Oxford Dictionaries' word of 2013 was "selfie"
Courtesy NASA
There are many perils with a "deep space" mission (here "deep space" means anything beyond the moon, given humankind's limited experience with interplanetary travel.) These include radiation, for instruments aboard the spaceship that carried Curiosity to Mars have found that deep space travelers would face worrying levels of radiation. The Radiation Assessment Detector aboard the vessel that took Curiosity to Mars found that a person traveling to Mars and back would receive 0.66 sieverts of ionizing radiation. This would potentially cause radiation poisoning and cancer. This has led considerable research into appropriate shielding.
Representation of a Russian Moon space ship at the margin in the Moon s orbit
Representation of a Russian Moon space ship at the margin in the Moon's orbit
A related obstacle is food. Longer hauls on the International Space Station (ISS) or deep space missions create problems with the food supply for astronauts. One solution rests with sugar-producing bacteria. These organisms could be a potential food source for astronauts, together with crops grown in zero-gravity.
A third area, and the focus of discussion here, is with bones. Since the Apollo missions of the 1970s medical scientists have understood how zero gravity causes problems with bone structure. The effects of prolonged weightlessness on the human body can be slow and subtle, yet, over time, bone damage results. Astronauts lose around 1 percent of bone mass per month spent in space.
Here the loss of bone mass that astronauts experience in space weakens the bone and this, if it occurs for a period exceeding one year, present problems when the person returns to a weight-bearing environment. The name for this effect is "spaceflight osteopenia."
A scene from  Gravity
A scene from 'Gravity'
Warner Bros. Entertainment
The condition causes bone to reform in a reaction to stress, becoming more dense in zones experiencing high stress and less dense in zones experiencing low stress. Scientists are particularly concerned about the effects of this on an astronaut on Mars. Here gravity is just one-third that of Earth and this would lead to an overall decrease in bone mass and density.
There are some measures that can be taken, including taking dietary supplements rich in calcium and vitamin D. However, more effective measures will be needed for the long haul. It is here where some recent research has made a breakthrough.
According to Melissa Gaskill of the International Space Station Program Office at the NASA Johnson Space Center, scientists have been looking at fish for the answers. On board the International Space Station scientists have been rearing freshwater Medaka fish over a period of 56 days. Medaka fish are also known as Japanese rice fish (Oryzias latipes).
The examination has centered on the jawbones and teeth of the fish to measure the effects of microgravity. Microgravity is close to weightlessness and zero-g, although there is a low gravitational force at work.
One reason for using fish to study microgravity is because fish grow relatively quickly and the bone structure is straightforward to measure, scan and photograph. In addition, Medaka have a short gestation period and produce lots of offspring. On the space station the fish were reared in the Aquatic Habitat in the Kibo module.
Zebrafish (Danio rerio)  an small tropical aquarium fish used in molecular genetics and medical rese...
Zebrafish (Danio rerio), an small tropical aquarium fish used in molecular genetics and medical research.
The research has found microgravity activates osteoclasts. These are types of bone cell that break down bone tissue. In normal circumstances, this is necessary for the maintenance, repair, and remodeling of bones of the vertebral skeleton. However, under zero gravity the production of these cells increases above the norm.
Scientists have been using the Medaka fish to determine the relationship between elevated osteoclast activity and reduced bone mineral density. To make study easier, the fish were engineered to have fluorescent osteoclast cells. Over time, particularly at night, the fish experienced periods of motionless.
The reason for the increased activity has been traced to abnormalities in osteoclast mitochondria (which produce the enzymes necessary for converting nutrients to energy.) The abnormalities relate to two genes. These genes appear to be activated under conditions of microgravity and there is a probably a connection with the brain, in that the brain senses microgravity and triggers a biochemical response.
The outcome is that medicines may be developed that target mitochondria dysfunction and this could restore the bone loss in space. To develop such space medicine will require further research.
The research is published in the journal Nature Scientific Reports. The paper is titled " Microgravity promotes osteoclast activity in medaka fish reared at the international space station."
This article is part of Digital Journal's Essential Science series. Other articles in the series are:
"Space-food for astronauts made from bacteria";
"Health effects of antibiotic use";
"Graphene makes improved night vision tech";
"Personalized medicines, the health innovation”;
Power paper can store electricity”;
"Why some rainbows are completely red";
"Bright white light affects animal reproduction";
"Low cost device restores speech to patients";
"Learn about the new field of neurogastronomy";
"How implanted coils help to fight lung disease;"
"Researchers locate the origin of cancer."