In 2015, astronaut Scott Kelly set off for the International Space Station while his twin, Mark Kelly, remained on Earth. Scott returned in 2016, and both brothers are now retired, but over the one year Scott spent in space, 10 teams of researchers in the US carried out a landmark study on the twins’ biological profiles (Scott was sending his samples from space). With the twins sharing the same genetic code, the researchers looked for variances in their bio-markers.
The results showed that a long stay in space can cause changes in the human body. These were epigenetic changes — chemical “tweaks” to DNA that can influence gene activity, without affecting the underlying genetic code itself. When epigenetic changes occur at the wrong time or place, the process can turn genes on or off at the wrong time and place. In Scott’s case, most of the changes were reversed within months of his return to Earth.
The findings have been published in the journal Science. What changed, what did not:
Telomeres: These are special features at the ends of each DNA strand. Telomeres tend to get shorter as one ages; however, certain factors can affect the rate of this shortening. In Scott’s case, the study identified a change in telomere length dynamics during spaceflight and within days of landing.
Gene expression: Samples taken before, during and after Scott’s mission in space revealed some changes in gene expression. These were different from the changes Mark experienced on Earth. Of the changes Scott experienced, most (about 91.3%) reverted to baseline after he returned, while a small subset persisted after six months. Some observed DNA damage is believed to be a result of radiation exposure.
Gut bacteria: Scott’s microbiome during flight was profoundly different from pre-flight. This could be due to the food he consumed in space, although other space-specific environmental factors may have also contributed. When he landed on Earth, Scott’s microbiome returned to pre-flight state.
Arteries: The inside of an artery wall can narrow due to plaque buildup. Researchers found indications of inflammation and carotid artery wall thickening in Scott during and immediately after his mission, but no such changes were observed in Mark. Researchers have not yet established whether this adaptation is reversible.
Some of the findings were encouraging for researchers:
Vaccination: Scott received three flu vaccines — on Earth, in space, and back on Earth — each a year apart. This study found that his body reacted appropriately to the vaccine.
Cognition: With few exceptions, Scott’s cognitive performance (such as mental alertness, spatial orientation, recognition of emotions) remained largely unchanged during his time in space, and relative to Mark on the ground.
(Source: NASA & Johns Hopkins University)