One year in space - what are the consequences?

NASA's twin study reveals far-reaching and sometimes unexpected changes

The identical twins Mark and Scott Kelly are both NASA astronauts, but only Scott spent a year on the ISS space station. © NASA
Read out

One year in space: An unusual twin study reveals the consequences astronauts have to expect in long-term missions. Because NASA astronauts Scott and Mark Kelly are identical twins - but only one remained in orbit for a year. The comparison reveals that there are some unexpected and far-reaching changes and damages, especially in genetic material - and not all of them are reversible. Surprisingly too: Spaceflight caused cognitive deficits - but only after landing.

Being an astronaut is unhealthy - as proven by experience from the Apollo missions, but also from the International Space Station ISS. Weightlessness makes muscles and bones dwindle, blood and water rise to the head. In addition, astronauts often get fever, viruses become active and the cardiovascular system shows lasting damage. Long space missions can cause long-lasting changes to the astronaut's brain, and could even threaten dementia on flights to Mars.

All these symptoms show up after just a few days to months in space. But in the near future humans will fly to Mars and live in lunar space stations. They would therefore spend years in space. "Only four people have completed space missions of more than a year so there is almost no experience with flights lasting more than six months, " said Francillin Garrett-Bakelman of Weill Cornell Medicine, New York, and her colleagues.

Scott Kelly at an outdoor mission at the International Space Station ISS. NASA

A twin in space

The remedy is a twin study of a special kind, because NASA astronauts Scott and Mark Kelly are identical twins. However, while Scott spent a year on the ISS, his brother Mark stayed on the ground. This enabled researchers to determine for the first time which physical and mental changes caused a long-term stay in space compared to a genetically identical comparator.

For the study, both brothers gave multiple urine, blood and saliva samples before, during and after the space visit. They then analyzed ten different research teams for genetic, microbiological and physiological parameters. In addition, both astronauts performed tests of their physical and mental performance several times over the course of the 25-month project. display

Telomeres: Rejuvenated in space?

Now the results are available and are sometimes quite surprising. It therefore seems clear that a long space mission affects the body and mind of a person in many ways. As expected, the researchers found changes in the cardiovascular system, as well as the immune system, the musculoskeletal system and the eyes. Increased inflammatory markers and altered messenger substances also indicated a physiologically increased stress level. In addition, Scott Kelly's gene expression was altered in more than 9, 000 loci, according to the researchers.

Unexpectedly, however, was another change in the genome: The telomeres in the cells of the ISS astronaut were in orbit longer these end caps of the chromosomes grew on average by 14.5 percent. "That really surprised us, " says Susan Bailey of Colorado State University. Because with stress and with age telomeres tend to be shorter. Scott Kelly's chromosomes seemed to rejuvenate.

Also strange: When Scott Kelly returned to Earth, his chromosome ends returned to the old state, but not all. Ironically, the few telomeres that had shrunk in space remained shorter afterwards. Why, is so far unclear.

Copying errors in the genome

Less surprising, but clearly negative is another genetic effect: During the space mission, the cells of the astronaut copying the DNA made significantly more errors than normal. They put parts of the chromosome in the wrong place or in the wrong place. "At the same time, genes that are linked to reactions to DNA damage have also been read a lot, " Garrett-Bakelman and her team report.

This suggests that staying in space causes increased damage and errors in the genome. The reason for this is the increased radiation exposure in Earth orbit, as the researchers explain. The astronaut was exposed to a radiation dose of 146 millisieverts on the ISS during the year - the equivalent of fifty years of natural background radiation on Earth.

Worrying too: even after returning to Earth, the copying errors in the chromosomes continued for months. "This could indicate radiation-related damage to the stem cell reservoirs of the cells, " said the scientists. In the long term, these radiation effects could significantly increase the cancer risk for astronauts.

Mental losses - after landing

But even in the mind of the astronaut, the long-term mission did not pass without a trace. During his time on the ISS, his cognitive performance did not diminish, but after his return to earth. The mental efficiency of the astronaut dropped even below the level before the space flight. "These deficits in the pace and precision of cognitive performance have been preserved for up to six months after returning to Earth, " Garrett-Bakelman and her team report.

Why these mental deficits only manifested after landing is so far unclear. For future Mars missions, however, that could mean that the astronauts are still doing quite well on the outbound flight and are up to all challenges. But when they land on the Red Planet, mistakes could slip in. "This could be a problem for the safe management of space missions - for example, after a landing on Mars, " say the researchers.

Effects more evident than expected

"The observed effects are thus broader and more pronounced than one would have expected - especially in beam-specific reactions such as genome instability, up-regulated gene expression and cognitive deficits, " writes Markus Löbrich of the TU Darmstadt in an accompanying commentary. He also emphasizes that the astronauts would be exposed to more than five times the radiation dose on a flight to Mars. Because outside the earth orbit lacks the protective shield of the earth's magnetic field.

"Understanding the details of these changes and their long-term consequences will therefore be important for future ventures, " says Löbrich. "On this point, the study by Garrett-Bakelman and her team is more than just a small step for humanity." (Science, 2109; doi: 10.1126 / science.aau8650)

Source: Science, NASA, Johns Hopkins, Weill Cornell Medicine, Colorado State University, University of California, San Diego

- Nadja Podbregar