Two new studies have analysed the impact of space travel on humans – and one could be of benefit here on Earth.
US scientists studying the effects of weightlessness on mice may have found a possible cure for muscle and bone loss in the elderly.
A team led by Se-Jin Lee and Emily Germain-Lee, from the University of Connecticut, sent mice to the International Space Station (ISS) for 33 days, and had them injected once a week with a chemical that inactivates two natural hormones, known as myostatin and activin A.
These hormones, Lee says, circulate in the blood and act together to limit muscle growth. “At high levels, [they] can actually cause the muscle to atrophy.” (The two hormones are also implicated in bone loss.)
They exist because, in the days before the modern industrialised world’s glut of high-calorie foods, the body needed enough muscle: but not too much.
“Muscle is a very metabolically demanding tissue,” Lee says. “[So] you don’t want to have any more than you absolutely need. I have argued that for us, this entire regulatory system is an evolutionary vestige.”
That vestige is a bad enough problem here on Earth, especially in the elderly and people with medical conditions that cause their muscles to fall into disuse. In space, it is especially problematic because we don’t want astronauts’ muscles to so thoroughly adapt to weightlessness that they can no longer stand up when they come home.
Traditionally, this problem is addressed with exercise, but Lee’s work opens the door to using myostatin/activin A inhibitors as medications to prevent muscle and bone loss not only on the International Space Station but on future trips to Mars.
“At the International Space Station,” Lee says, “astronauts are able to maintain extensive workout regimens. For longer missions the type of exercise equipment the vehicles can accommodate will almost certainly be more limited.”
The findings are published in a paper the journal Proceedings of the National Academy of Sciences.
Meanwhile, another group of scientists has been studying the effect of weightlessness on astronauts’ brains.
In a paper published in Science Advances, a team of Belgian, Russian, Australian and German researchers took MRI images of the brains of 11 Russian cosmonauts before and twice after they spent an average of nearly six months on the ISS.
“This was one of the first studies to look at the effects of spaceflight on the brain,” says Steven Jillings, a neuroscientist at Belgium’s University of Antwerp.
One finding was an increase in grey matter – what we conventionally think of as brain cells – in portions of the brain related to initiating and controlling muscle movement, including fine motor skills.
Furthermore, it seems to be a lasting effect, still present when the cosmonauts’ brains were re-examined seven months after their return to Earth.
Permanent changes in your brain might sound scary, but in this case they are actually a good thing, Jillings says, because they indicate that the cosmonauts acquired new skills (basically how to move around in zero gravity), which their brains retained.
“They don’t use it on Earth,” he says, “But we suspect that when they go on their next missions, they are actually able to adapt more quickly.”
The other change was in the distribution of cerebrospinal fluid, which surrounds the brain and spinal cord and is found deep inside the brain in cavities, called ventricles. During spaceflight, Jillings says, it shifts downward in the skull, causing the brain to move upward – “a direct physical effect of being in a weightless environment.”
After return to Earth, however, it doesn’t immediately return to its normal distribution within the skill. “It seems that it is a very slow recovery process,” he says.
What that means is unclear. It has been known for some time that astronauts can have problems with their visual acuity after returning to Earth. “The mechanism for development of this impairment is not known yet, but it is very much thought that it has to do with this fluid redistribution,” Jillings says.