It’s a tougher life in space than we thought
Studies suggest not only bone and muscles are affected. Nick Carne reports.
Two new studies confirm that life in space is pretty hard on the body.
Scientists have known for some time that extended periods away from Earth come with some risks, such as muscle and bone loss due to the effects of microgravity, but now it appears it could adversely affect cells in your immune system and even change the make-up of your brain.
The first study, by US researchers led by Richard Simpson from the University of Arizona, looked at the impact of spaceflights of six months or more on natural killer (NK) cells – white blood cells that kill cancerous cells in the body and prevent old viruses from reactivating.
"Cancer is a big risk to astronauts during very prolonged spaceflight missions because of the exposure to radiation," Simpson says. "[NK-cells] are also very important to kill off virally infected cells. When you're in the space station, it's a very sterile environment; you're not likely to pick up the flu or a rhinovirus or some community-type infection, but the infections that are a problem are the viruses that are already in your body.
“These are mostly viruses that cause things like shingles, mononucleosis or cold sores. They stay in your body for the rest of your life, and they do reactivate when you're stressed."
In their study, the researchers compared blood samples of eight crew who completed missions to the International Space Station (ISS) with healthy individuals who remained on Earth. Blood samples were taken before launch, at several points during the mission and after the astronauts' return to Earth.
The results – reported in a paper published the Journal of Applied Physiology – show that NK-cell function is impaired in astronauts as compared with pre-flight levels and ground-based controls. At flight day 90, NK-cell cytotoxic activity against leukaemia cells in vitro was reduced by approximately 50% in ISS crew members.
The effect appears to be more pronounced in first-time astronauts, as opposed to those who have already been in space. "Serendipitously, we found that half our crew members had flown before, and the other half hadn't," Simpson says. "So we were able to just split them in half to see if there was an effect, and there was. The 'rookies' had greater drops in NK-cell function compared to the veterans."
The differences could be chalked up to age or stress, Simpson says, assuming the rookies, who are generally younger than the veterans, would find space travel more stressful than those who had done it before.
The next question is, how do we mitigate these effects and prevent the immune system from declining during space travel? "In order to do that,” says Simpson,” you have to first figure out what's causing the decline: Is it stress? Is it microgravity? Is it radiation? Is it a plethora of things? When we figure that out, we can try to find ways to directly target those factors and mitigate them."
The second study, led by Jessica Lee from the University of Florida, US, found that spending time in space is changing the make-up of astronauts' brains.
As well as an upward shift of the brain within the skull, they found an increase in “free water” and changes to the white matter near the top of the brain. These were most common in astronauts who spent extended periods in space or who were involved in more than one space mission.
The findings are reported in a paper published in the journal JAMA Neurology.
The researchers examined pre- and post-flight diffusion magnetic resonance imaging (dMRI) scans, provided by NASA, of 15 astronauts (12 males and three females). Seven had completed a space shuttle mission of about 30 days and eight a long-duration ISS mission (around 200 days).
“Free water redistribution with spaceflight likely reflects headward fluid shifts occurring in microgravity as well as an upward shift of the brain within the skull,” they say. “White matter changes were of a greater magnitude than those typically seen during the same period with healthy aging.”
Future prospective assessments are required to better understand the recovery time and behavioural consequences of the reported brain changes, they add.