Spending weeks or months in space can lead to muscle loss, deterioration in cognitive ability and bone formation, and even vision problems for astronauts. As we prepare to send astronauts deeper into space, researchers are investigating how these even-longer journeys will affect the human body.
"While short trips, like the times astronauts traveled to the moon, may not expose them to this level of damage, the real concern is lasting injury from a long trip, such as a Mars [mission] or other deep-space missions, which would be much longer," Kamal Datta, the study's lead investigator and project leader of the NASA Specialized Center of Research (NSCOR) at Georgetown University Medical Center, said in a statement. [What Does Space Travel Do to Your Gut Microbes? (Video)]
To simulate how galactic cosmic radiation in deep space will affect future astronauts, researchers at Georgetown University Medical Center studied radiation's impact on the small intestine of mice. Their findings suggest that exposure to a low dose of iron radiation could cause serious gastrointestinal (GI) damage, as well as tumor growth in the stomach and colon, according to the statement.
It’s important to consider how radiation will impact astronauts on longer space missions because the digestive tract is an important source of immune function in the body. Generally, brand-new cells replace the top layer of cells in our GI tract every three to five days. However, heavy-ion radiation tends to disrupt this process, causing the GI tissue to break down and causing long-term problems, according to the study.
When new cells can't replenish properly, it affects how the human body absorbs nutrients and, as a result, causes abnormal or cancerous tissue growth.
Galactic cosmic radiation doesn't affect humans on Earth, because the planet's magnetosphere protects us. However, heavy ions such as iron and silicon that are found in deep space can damage the human body, because these atoms have a "greater mass compared to no-mass photons such as X-rays and gamma (γ)-rays, [which are] prevalent on Earth, as well as low-mass protons in outer space," Datta said in the statement.
For the study, researchers exposed one group of mice to heavy ions, while another group received only gamma-rays. The scientists then compared the results from these two groups with those of an unexposed control group.
The mice exposed to iron radiation exhibited cancerous tissue growth, as well as DNA damage that increased the mice's number of senescent cells, a type of cell that is incapable of regular cell division or regeneration. Specifically, these cells can slow down the replacement of healthy GI cells and, as a result, slow down normal GI function.
Senescent cells "generate oxidative stress and inflammatory molecules that induce more damage," Datta said in the statement. "This greatly affected migration of cells that are needed to replace the intestinal lining, which slowed down GI functioning."
The radiation appeared to cause permanent damage, according to the study. Also, the researchers suggested that exposure to heavy ions may cause similar damage responses in other organs.
"With the current shielding technology, it is difficult to protect astronauts from the adverse effects of heavy-ion radiation," Datta said. "Although there may be a way to use medicines to counter these effects, no such agent has been developed yet."
While the mice were used only as model of what astronauts could experience, the researchers said they plan to continue studying the effects of radiation in mice so that they can better understand the risk astronauts face during longer-duration missions.
"It is important to understand these effects in advance, so we can do everything we can to protect our future space travelers," Datta said.
The findings were published Monday (Oct. 1) in the journal Proceedings of the National Academy of Sciences.