Scientists who study astronauts and the effect of space flight on their bodies had found some odds things over the years. NASA had a unique opportunity to study long-term effects a few years ago when they used identical twin astronauts Scott and Mark Kelly to compare an astronaut's (Scott's) physical condition during and after a year on the International Space Station with his twin (Mark, who had retired) on earth. The comprehensive results of that study have been published in the magazine Science. The results are not pretty.
Scott’s immune system was generally turbulent during his year in space: Many of his immune-related cellular pathways were disrupted, including the adaptive immune system, innate immune response, and the natural killer-cells that protect the body from cancers like leukemia and viruses. (The result confirms a shocking study published in January that compared the immune systems of eight astronauts who completed spaceflights longer than six months with healthy adults on Earth: Just 90 days into their flights, the astronauts’ natural-killer cells were 50 percent less capable of fighting leukemia cells.) Scott’s cognitive function was also whacked: He got dumber on the ISS.
The human body is wonderfully adaptive, and almost all of these changes were transient: Scott returned to normal within six months of returning to Earth. He became his old self, except for the ordinary depredations of age. But some of the effects of spaceflight left their mark. Scott got dumber on the ISS, but he stayed dumber, too. The decline in the speed and accuracy of his mental functions persisted six months after his mission.