There is an obstacle that will make missions from Earth to Mars particularly difficult and risky for astronauts: the effects of the lack of gravity and cosmic radiation on the immune system, which are probably worse than what was thought up till now. This is suggested in a study published in the Journal of Applied Physiology by researchers from the Universities of Arizona,  Texas and Louisiana, as well as the NASA-Johnson Space Center, who examined the pattern of one of the most important “categories” of lymphocytes that protect the body against viral infections and tumors, i.e. so-called Natural Killer cells (NK), in the blood of six astronauts that spent six months in the International Space Station.

Samples were taken of the astronauts’ blood prior to launch, several times during their mission and, finally, when they returned to our planet. These were then compared with blood samples taken from colleagues that had remained on Earth. And the researchers discovered that, after only 90 days, the effectiveness of NK-lymphocytes against potentially leukemic cells was reduced by 50% compared to that the of NK-cells of the astronauts that had remained on Earth, as well as the lymphocytes in the blood of the same astronauts taken prior to launch.

Furthermore, it was found that the change in NK-cells was more pronounced in first-time astronauts, as opposed to those that had already spent extended periods of time without gravity, probably due to the fact that young astronauts are more stressed when they face their “baptism” in space compared to their veteran counterparts, who already know what to expect – and stress, as it is well-known, heavily influences the immune system.

Now research will continue in order to understand the exact causes of the loss of effectiveness of NK-cells (microgravity? Stress? Age? Cosmic radiation?). And only when all the reasons for this immune system debacle are clear will it be possible to start to study specific remedies, which will be very important in view of future missions – such as those to Mars, scheduled for 2030 – which will probably last at least three years. Even if spaceships are almost sterile environments, each human carries millions of viruses and bacteria and, sometimes, cancer cells that, if not counteracted by an efficient immune system, could put the health of astronauts in serious danger.

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