Different types of bone cell either build bone up or break it down. For weight-bearing bones, breakdown cells become more active when there is no impact on the bone, such as in microgravity. "Astronauts experience around 20 to 30 per cent bone loss," says Sara Tavella at the University of Genoa in Italy.
Astronauts exercise and take calcium supplements to limit damage, but it is very difficult to return the bone to its original state back on Earth, says Tavella.
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To examine other options, her team sent six mice up to the International Space Station. Three of the mice were genetically modified to produce extra pleiotrophin (PTN) - a protein involved in bone development.
The mice with extra PTN were protected from the breakdown of bone - losing only 3 per cent of the volume of their spine compared with a 41.5 per cent decrease in the normal mice.
The protein treatment could be investigated for use in astronauts preparing for space, says Tavella.
