Ever since the first astronauts went up, we've known that life in space profoundly affects the human body. To investigate the extent of those changes, NASA conducted a comprehensive study comparing the genes and biology of identical twins Scott and Mark Kelly, after Scott spent almost a year in space while Mark stayed on Earth as a control. And now the results of that study have finally been released.

As part of the study, Scott lived on the International Space Station for 340 days over 2015 and 2016, while his brother, also a retired astronaut, went about his regular life on the ground. The idea, of course, is that because twins share 100 percent of their genetic makeup, they're a great window into the effects of the space environment on the human body.

In this case, 10 research teams intensely studied different aspects of the Kelly brothers' physiology during the spaceflight and for six months after Scott's return to Earth. The data gathered will help inform space missions for probably decades to come, including future astronaut diets, exercise regimes, and health and safety measures as we send humans back to the Moon and eventually, to Mars.

One of the most interesting findings was to do with Scott's telomeres. These sections of DNA sit at the tips of chromosomes and protect DNA from damage when cells divide, kind of like the little plastic bits on the ends of shoelaces. They naturally get shorter as we age – but the scientists noticed that Scott's actually got longer while he was in space. Within days of returning to Earth they shrank drastically, before returning to average length within six months. Mark's, meanwhile, stayed stable throughout the test period. This is basically the opposite of what was expected, which could have intriguing implications for aging in space.

Another important finding is that the flu vaccine works in space, which wasn't a guarantee. Scott was the first person to ever receive a vaccine in space, and it was found that his immune system responded as it should. That bodes well for longer missions in future where vaccinations will be an important procedure.

Gene expression was also found to differ between Mark and Scott. While space seems to have altered gene activity to a higher degree than usual, more than 90 percent of these changes reverted back to normal once back on Earth. Interestingly though, roughly seven percent persisted longer than six months. These gene expression changes can be linked to many of the other findings in the study. DNA damage was also observed, which NASA chalks up to radiation exposure.

Scott's cognitive abilities appeared to be relatively unchanged during his time in space, but interestingly, he experienced a decrease in speed and accuracy of cognition after returning to Earth, which persisted for the six-month period. But, NASA says, that could be a result of readjusting to Earth's gravity, and the stresses of a busy schedule afterwards.

Perhaps unsurprisingly, Scott's gut microbiome was drastically different during flight compared to beforehand. This is most likely due to the very different diet that astronauts have to eat, which includes mostly freeze-dried foods. What wasn't known though was whether these changes might be long-term afterwards, but thankfully the study found that the microbiome returned to normal within six months. The data could help inform changes to astronaut diets that foster healthier gut bacteria.

Among the many other health effects observed in Scott, the team found evidence of carotid artery wall thickening, elevated levels of the protein AQP2 – which may play a part in vision problems reported in astronauts – and folate, and other epigenetic changes.

The data gathered through this comprehensive study will no doubt continue to be trawled through for years to come. It will not only help inform future space missions but potentially unlock more general health benefits for us Earth-bound humans too, including new treatments for disease and better insights into aging.

The research was published in the journal Science. Some of the results are outlined in the video below.

Source: NASA [1],[2]