Scientists finally discover why space travel weakens our immunity

We know that space makes us sick: astronauts routinely get skin rashes or viruses while aboard the International Space Station (ISS). But scientists now know why.

A new study shows that space travel literally changes how genes in white blood cells work, preventing them from carrying out their usual function of recognizing and combating infections.

“These results are important considerations of risks to health during spaceflight and space exploration,” Myles Harris, an associate lecturer at University College London (UCL) who was not involved in the study, told BBC Science Focus.

The study, published in Frontiers In Immunology, describes how the rapidly decreasing strength of our immune systems in space is likely caused by a phenomenon known as ‘fluid shift’.

Fluid shift involves blood plasma, which transports white blood cells around the body, moving from the lower body to the upper body due to microgravity (that low gravity state that makes astronauts appear to be weightless). This reduces the volume of both the plasma and the important white blood cells.

But it’s not all bad news – as long as you return to Earth. Within one year of returning from a six-month stint at the ISS, astronauts’ volumes of white blood cells return to normal. This is why astronauts are more vulnerable to infection within their first month back on Earth.

Individual recovery times are likely to depend on personal factors, but this research is yet to take place.

The research team, from the University of Ottawa, Canada, studied white blood cell genes from 14 astronauts who had spent 4.5-6.5 months on the ISS.

Before, during and after the flight, the astronauts had to have 4 millilitres of blood drawn a total of 10 times.

“A weaker immunity increases the risk of infectious diseases, limiting astronauts’ ability to perform their demanding missions in space,” said Dr Guy Trudel, professor of cellular and molecular medicine at the University of Ottawa and one of the paper's authors.

“If an infection or an immune-related condition was to evolve to a severe state requiring medical care, astronauts while in space would have limited access to care, medication, or evacuation.”

The next step in the scientists’ research will be designing ways to prevent immune suppression during long-duration space flights.

According to Harris, this “would also make valuable contributions to the design of personalised medicine on Earth.”