Millions of years of evolution may have rendered us Earth-locked, a Canadian-Russian research team reports. Zero- and microgravity conditions seem to severely impair our immune systems’ ability to function, so much so that they’d struggle to deal with even minor viruses like that of the common cold.

A team of Russian and Canadian researchers have analyzed the protein make-up in the blood of 18 Russian cosmonauts to get an idea of their immune system health. They report that the crew, who spent six months aboard the International Space Station, showed signs of significantly weakened immune systems that would struggle to deal even with minor pathogens.

No gravity, no service

“The results showed that in weightlessness, the immune system acts like it does when the body is infected because the human body doesn’t know what to do and tries to turn on all possible defense systems,” said Professor Evgeny Nikolaev of the Moscow Institute of Physics and Technology, the Skolkovo Institute of Science and Technology, and paper coresponding author.

Our bodies, like those of all other organisms on Earth, have been tailored by evolution to adapt to specific conditions. It makes perfect evolutionary sense to adapt to the place you’re living in, but humans are now trying to do something that no life before us ever tried — we want to leave the planet. That’s quite problematic since it takes us out of the set of conditions we’re designed to function in.

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Environmental factors associated with spaceflight, most notably microgravity and radiation exposure, tend to mess up our bodies’ inner workings. Our metabolism, heat regulation systems, heart rhythm, muscle tone, bone density, vision, our respiratory systems, they all go a bit haywire once you take us off the planet.

It all adds up to take a toll. Astronauts who went on deep space or lunar missions were five times more likely to die from cardiovascular diseases than their counterparts who stayed in low orbit, or people who never left Earth (around 43% compared to under 10% for the latter). And that’s considering that astronauts are way fitter than the average Joe and have access to the best medical care available.

To get a better idea of how space travel impacts human physiology, the team looked at the level of 125 proteins in the blood of astronauts who spent six months aboard the ISS. Proteins underpin virtually all complex tasks inside the body, so by looking at their state in the blood researchers could infer the state of the crew’s immune systems. Samples were first taken from the cosmonauts 30 days before they left for the ISS to establish a baseline. To track changes in their immune systems, the team also took blood samples immediately after the cosmonauts returned to Earth, and seven days later. Individual proteins were counted using a mass spectrometer.

The results aren’t very encouraging at all

”When we examined the cosmonauts after their being in space for half a year, their immune system was weakened,” said Dr Irina Larina, the first author of the paper, a member of Laboratory of Ion and Molecular Physics of Moscow Institute of Physics and Technology. “They were not protected from the simplest viruses. We need new measures of disorder prevention during a long flight.

It doesn’t bode well for future explorers, as our immune system is what’s literally keeping us alive all day, every day. The effects were manageable, although severe, after only six months. But future missions are likely going to take much longer. A one-way trip to Mars, our closest viable candidate for a colony, would take around six to eight months — and colonists wouldn’t have the medical means and infrastructure available on Earth, meaning they’ll have to rely on their now weakened immune systems much more than the cosmonauts. So it can become a problem.

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However, we can get to work on understanding and then address these changes before we start poking around the final frontier.

“We must understand the mechanism that causes disorders. If we find the pathways that are affected by the weightlessness, we will be able to find the target for the remedy and we’ll be able to offer new pharmaceutical products that will prevent these negative processes.”

The paper “Protein expression changes caused by spaceflight as measured for 18 Russian cosmonauts” has been published in the journal Nature Scientific Reports.