The twin study, which took place between 2015 and 2016, is the first such study ever conducted by NASA. The study involved astronaut Mark Kelly on Earth and his identical twin brother Scott Kelly in space. After Cott Kelly returned to Earth, NASA studied the effects of exposure to space on his health by comparing his data with that of his brother Mark.
NASA's research details some important findings, including the impact of space life on Scott Kelly telomeres. According to the space agency, Scott's white blood cell telomeres were unexpectedly longer in space, but shorter after returning to Earth. Six months later, the length returned to the average; Mark Kelly's telomere length remained stable at the same time.
In addition, NASA said its research found that Scott Kelly's immune system responded appropriately in space, including to influenza vaccines. As NASA said before, researchers also found variability in gene expression, most of which returned to normal six months after returning to Earth.
This exception involves a "small number" of genes associated with DNA repair and the immune system that did not return to baseline after Scott Kelly's space life. J.D. Polk, chief health and medical officer at NASA headquarters, explained that:
The study of twins is an important step in understanding epigenetics and gene expression in human space flight. Thanks to the twin brothers and a group of investigators who worked tirelessly together, valuable data collected from twin studies can help illustrate the need for personalized medical care and its role in maintaining astronauts'health in deep space exploration, as NASA is on a mission to the moon and Mars.