"We found that astronauts had significantly less fat in their bone marrow about a month after returning to Earth," said senior study author Dr Guy Trudel. "We think the body is using this fat to help replace red blood cells and rebuild bone that has been lost during space travel."
Previous research from the same team showed that in space astronauts' bodies destroyed on average 54 per cent more red blood cells than they normally would on Earth, resulting in what is known as "space anaemia."
"Thankfully, anaemia isn't a problem in space when your body is weightless, but when landing on Earth and potentially on other planets or moons with gravity, anaemia would affect energy, endurance and strength and could threaten mission objectives," Trudel added.
The new study involved MRI scans of the astronauts' bone marrow at multiple time points before and after a six-month mission at the International Space Station.
The researchers found a 4.2 per cent decrease in bone marrow fat about a month after returning to Earth. This gradually returned to normal levels and was closely associated with increased production of red blood cells and restoration of bone.
"Since red blood cells are made in the bone marrow and bone cells surround the bone marrow, it makes sense that the body would use up the local bone marrow fat as a source of energy to fuel red blood cell and bone production," said Trudel. "We look forward to investigating this further in various clinical conditions on Earth."
The research also suggests that younger astronauts may have an increased ability to harness the energy from bone marrow fat, and that female astronauts' bone marrow fat increased more than expected after a year.
The research team believes the study could also shed light on diseases such as osteoporosis, metabolic syndrome, aging and cancer, which are associated with increases in bone marrow fat.
Various studies have demonstrated the dramatic impact that space can have on the human body. One team showed how astronauts frequently suffered from ocular damage, with their eyeballs being reshaped and folds forming on the retina. Another found they frequently suffered from 'leaky gut' problems, while the brains of astronauts are also shown to reduce in size after long bouts in orbit.
