Mice that spent less than two weeks aboard Space Shuttle Atlantis have been found to have developed significant liver damage, raising concerns about the impact of long-term spaceflight on human health.

The mice spent just 13.5 days in aboard the space shuttle in 2011, but when they returned to Earth scientists from the University of Colorado Anschutz Medical Campus spent several years examining the mice’s organs and have found indications of non-alcoholic fatty liver disease (NAFLD), as well as possible early signs of fibrosis.

“It generally takes a long time, months to years, to induce fibrosis in mice, even when eating an unhealthy diet,” said study lead author Dr Karen Jonscher, an associate professor of anesthesiology and a physicist at CU Anschutz.

“If a mouse is showing nascent signs of fibrosis without a change in diet after 13.5 days, what is happening to the humans?”

While there has been considerable previous research on the impact of spaceflight on humans, most has focused on the brain, bones, muscles and the cardiovascular system.

“Prior to this study we really didn’t have much information on the impact of spaceflight on the liver,” said Jonscher. “We knew that astronauts often returned with diabetes-like symptoms but they usually resolved quickly.”

The findings raise significant concerns about the impact of long-term spaceflight on human liver health, in particular for the mission to Mars, which will see astronauts spend over a year in space.

It is thought the damage the mice experienced was the result of microgravity, although it could also be caused by the stress of spaceflight and re-entry.

“Whether or not this is a problem is an open question,” she said. “We need to look at mice involved in longer duration space flight to see if there are compensatory mechanisms that come into play that might protect them from serious damage.”

The research, which was published today in the journal PLOS ONE, is likely to prompt further study, particularly on mice who have spent longer periods in space.

“Further study in this area is merited and analysis of tissues harvested in space from mice flown aboard the International Space Station for several months may help determine whether long-term spaceflight might lead to more advanced hepatic injury and whether damage can be prevented,” said Jonscher.

Medical studies of NASA astronaut Scott Kelly and Roscosmos cosmonaut Mikhail Kornienko, who recently returned from a year-long stay aboard the International Space Station, may also provide further insight.