At least, that was what the results of a recent study conducted by the University of Colorado’s Anschutz Medical Campus suggest. After examining a group of test mice that spent two weeks in space aboard STS-135 – the final mission of NASA’s space shuttle program – they concluded that spending prolonged periods of time in space could in fact result liver damage.
For some time now, scientists have understood that exposure to zero-gravity or micro-gravity environments comes with its share of health effects. But so far, the research has been largely confined to other areas of the human body. Understanding the effects it has on internal organs and other aspects of one’s health are of extreme importance as NASA begins preparations for a crewed mission to Mars.
While the effects of long-term stays in space has been the subject of much scientific and medical study, the focus thus far has been on the effects to bone density and muscle mass. A good example of this is the Twins Study conducted by NASA’s Human Research Program (HRP), which researched the effects on an astronaut Scott Kelly’s body after he spent a year aboard the International Space Station.
The study reported that, “without gravity working on your body, your bones lose minerals, with density dropping at over 1% per month.” Similarly, a report by the Johnson Space Center – titled “Muscle Atrophy” – stated that “astronauts experience up to a 20 percent loss of muscle mass on spaceflights lasting five to 11 days.”
These and other studies have shown that exposure to zero-gravity or micro-gravity environments can take a toll on an astronaut’s body, their senses (i.e. visual acuity and hearing), as well as their vestibular (sense of balance and orientation) and cardiovascular systems. However, this most recent study was the first to examine the effect of spaceflight on the liver.
As Prof. Karen Jonscher – an associate professor of anesthesiology and a physicist at CU Anschutz, and the study’s lead author – explained in a university press release: “Prior to this study we really didn’t have much information on the impact of spaceflight on the liver. We knew that astronauts often returned with diabetes-like symptoms but they usually resolved quickly.”
Though temporary, these diabetes-like symptoms showed that there is a link between micro-gravity and metabolism. As the major organ of metabolism, it had been theorized that the liver could be a possible target of the space environment as well. However, until now, the question of whether or not the liver itself was effected remained an open one.
But after Jonscher studies liver samples that were taken from the rats, they found that the time they spent in space appeared to activate specialized liver cells that may go on to induce scarring and cause long-term damage to the organ. All told, the rats only spent thirteen and a half days in space during the final flight of Space Shuttle Atlantis (in July of 2011). As such, the results were quite startling.
Essentially, Jonscher’s team found that spaceflight resulted in increased fat storage in the liver, which was accompanied by a loss of retinol (an animal form of Vitamin A) and changes to levels of genes responsible for breaking down fats. As a result, the mice showed signs of nonalcoholic fatty liver disease (NAFLD) and potential early indicators for the beginnings of fibrosis, which can be one of the more progressive consequences of NAFLD.
Naturally, these findings raise concerns about the effects space travel would have on astronauts. “The question is,” said Jonscher, “how does that affect your liver? It generally takes a long time, months to years, to induce fibrosis in mice, even when eating an unhealthy diet. If a mouse is showing nascent signs of fibrosis without a change in diet after 13 ½ days, what is happening to the humans?”
Another interesting aspect of the research is the parallels it shows with health problems here on Earth. As the name would suggest, NAFLD can be caused by subsisting on a diet that is overly-rich in saturated fats. The abuse of alcohol has similar effects, damaging the liver to the point that it is no longer able to maintain regular metabolic and regulatory processes. In addition, there is a correlation between these results and the results of inactivity and aging.
In fact, as was also indicated by NASA’s 2001 HRP study, the rate of bone loss for elderly men and women on Earth is from 1% to 1.5% per year, consistent with what astronauts in space experience. And the CU Anschutz study noted similarities between the muscle atrophy the mice experienced and humans who experienced prolonged periods of bedrest (i.e. patients recovering in hospital).
So really, it would seem that the effects of prolonged time spent in space, and/or space travel, will result in the same kinds of physical changes that come from a life of inactivity, alcoholism, and aging – possibly all rolled into one. But before anyone starts thinking that this should deter us from space travel and exploration, Prof. Jonscher admits that the study does leave some room for doubt.
“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. 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.”
In addition, NASA ensured that its astronauts maintain a physical and nutritional regimen to minimize the health effects of space travel. Whether or not they will be sufficient for long term missions remains to be seen. In any case, the research conducted by CU Anschutz and other institutions on the effects of time spent away from Earth is of great importance, especially when one considering NASA and other space agencies long term exploration plans for the future.
Whether it is a mission to Mars, which will involve a year spent in space, or missions back to the Moon, knowing the long-term effects of zero-gravity or reduced gravity are paramount!
Further Reading: University of Colorado