NASA’s Twin Astronaut Study

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Have you heard about NASA’s Twin Astronauts? Most of you probably know the name, Scott Kelly. He’s a retired astronaut who holds the current U.S. record for the longest ever single spaceflight, clocking in at 342 consecutive days in space. Some of you may also know that he has an identical twin “Mark Kelly”, who is also an astronaut. Mark and Scott Kelly were the central figures in a brand new, totally unique twin study. NASA just published the results that let us know, in unprecedented detail, what happens to our bodies during long-term spaceflight. So, let’s learn what NASA’s twin astronaut study revealed us.

Expectations from NASA’s twin astronaut study

In the decades since first sending humans into space, we have been monitoring spaceflight-induced physiological changes in hundreds of astronauts. We can compare an individual to themselves before, during, and after a mission. Allowing NASA to develop countermeasures against issues like decreased bone density and decreased muscle mass. But so far, we are most familiar with the results of 1-4 months of spaceflight and comparing an individual to themselves doesn’t clearly let us know what could be caused by spaceflight vs. something that may have happened to that individual anyway. If we are expecting humans to survive years for something like transport to Mars, how do we prepare for that? How do we know what’s going to happen to our bodies?

Mark Kelly and Scott Kelly-NASA’s twin astronaut study
Mark Kelly and Scott Kelly

Well, Scott and Mark Kelly presented an incredibly exciting opportunity for NASA. While Scott spent a year in space, Mark served as his ‘genetically matched ground control’. Both twins were monitored closely before, throughout, and after the mission. Physiologically, genetically, and cognitively creating a massive amount of data in the first twin study of its kind. Some things changed during spaceflight that, while super interesting and important to keep measuring in future studies, don’t seem to pose a significant health risk. For example, body mass decreased, gut microbiome composition changed, and inflammation increased—all temporarily. Plus, the flu vaccine works just as well on someone in space as it does for someone on earth, which is a relief.

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Then we have got the medium-risk stuff. Stuff we may need to be careful about. Urine sample metabolites indicated that spaceflight could interrupt collagen regulation in the body. While we may most often hear about collagen in the context of our skin, it’s also part of all our veins and arteries and valves. Disturbance in its production and incorporation could result in issues like blood pooling at the bottom of our legs or issues with blood pressure regulation. And about telomeres—these are the caps on the end of your chromosomes that protect your DNA from damage and that deteriorate as we age.

Effects on Telomeres

Scott Kelly’s telomeres actually lengthened during his year on the ISS. But then shortened rapidly and significantly when he returned to Earth. They have since recovered to around pre-spaceflight length but given the essential nature of telomeres in protecting genomic integrity and the role we think they play in aging. Further research into this aspect of space-induced genetic changes could be really fruitful. Not only for spaceflight but for other areas of science and medicine. And now for the high-risk stuff, the stuff we really need to work on solutions for.

A comprehensive suite of computerized tests indicated that while some measures of cognitive function increased, especially early in the mission, other cognitive functions. Like emotion recognition and abstract matching accuracy actually declined during spaceflight, along with cognitive speed. And these declines persisted for about 6 months after return to Earth. In a weightless environment, our veins and arteries can also get a little confused. Usually, they have to work with or against Earth’s gravity to move blood around our body. But in microgravity, we see thickening of vascular walls, an increase in vascular stiffness, and a ballooning effect in the vasculature of the upper body. We are actually still not sure if all of this is reversible after an astronaut comes back to earth, that remains to be seen.

What we know from previous experiments?

Observations made in many other astronaut’s spaceflight is associated with altered optical function. We see swelling of the optical disc, a flattening of the actual globe of the eye, along with other structural changes, which can lead to onset of blurry vision, blind spots, and more. We have not been able to pinpoint what causes these changes but they are obviously not good for your eyesight and may be permanent. And lastly, blood samples- before, during, and post-flight determined that spaceflight can significantly increase genotoxic stress.

Other significant results from NASA’s twin astronaut study

Space is highly radioactive, and while galactic cosmic rays may sound awesome, they can really do a change on your DNA. Cytogenetic analysis, which means looking at changes in your chromosomes, revealed higher levels of genomic instability for the spaceflight twin. This comes in the form of increased chromosomal translocations and inversions, which can be linked to disorders like infertility and cancer. Genetic analysis also revealed dysregulation of genes, especially those associated with immune function and DNA repair. These changes did not return to normal when they got back to Earth. All this talk of DNA changing may make it easy to ask the question, “Are they still twins?”. The answer is YES.

Media outlets a while back went a little overboard with the ‘news’ that 7% of Scott Kelly’s DNA was different. If 7% of Scott’s genes were completely different, not only would he not be Mark’s twin anymore, he would be an entirely different species. The real way to think about it is that yes, some genetic mutation occurred, but most of the change was epigenetic change. This means that something like DNA methylation, or a little add-on unit to a gene, changed the expression of the gene, not the actual makeup of the DNA itself. This can result in upregulation or downregulation of the genes in charge of things like immune function and bone growth. So yes, they are still related.

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All of this data represents, as the researchers put it, “a uniquely controlled and integrated framework for comprehensively quantifying astronaut biology in space”. And opens up so many exciting questions that are going to be fascinating to build on. Even though NASA doesn’t currently have any more twins in the pipeline, this kind of research can continue with those who take on longer and longer spaceflights. Building a better understanding of the effects of long-term spaceflight on the body and the mind will prepare us to test even more spaceflight boundaries that no human has ever broken before. While hopefully keeping us all in one piece.


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