NASA's Twin Study Finds a Year in Space is OK For Your Health

The results of the study featuring twin astronauts Mark and Scott Kelly are officially in.
Jessica Miley

The final results of the NASA study on twins has been published in Science Journal. The research examined twin astronauts, Scott and Mark Kelly.


Fifty-year-old Scott spent a year aboard the ISS in 2015 while his identical twin stayed safe on planet earth. Both men were subject to close scrutiny, before during and after their year of separation to determine what effects space has on the human body.

Initial Results Caused Major Confusion

Initial results from the study were released both in 2017 and 2018. Reporting at times led some genuine confusion about the effects of space on humans. But with the final findings now published, NASA and other space agencies can clearly see what happens to the human body after it spends prolonged periods of time off our planet.

The research will help make astronauts and other space explorers stay safe on future missions. Overall the study confirms that Scott Kelly was comparably happy and healthy during his year in space compared to his earthbound brother.

Things Will Return to Normal

It also states that most of the small changes spotted in Scott returned to normal within six months time. “I think it’s reassuring to know that when you come back things will largely be back to the same,” said Michael Snyder, one of the study’s lead investigators.

When preliminary results were released last year many news outlets wrongly reported that 7 percent of Scott’s DNA had changed. Now if that were true the astronaut would have become an entirely new species.

Gene Expression Changed

What actually happened was that roughly 7 percent of his DNA had changed expression during his time in space. Basically, the genes the carrying out of instructions in a cell’s genome had altered slightly and that these changes were still observable six months after his return.

But it’s important to note that Marks DNA also went through some expression changes. That’s because our environment has the ability to shape our gene expression and can be affected by lifestyle choices like drinking and smoking that Scott was unable to enjoy.

Small but Important Differences

While most of these changes were tiny and have no real impact on either of the twins overall health (at least not that we know now). They are important for scientists to understand how the body does react to long periods of time in space.

One notable example of this that Scott’s eyes developed a thicker retinal nerve after a few months on the ISS. The same phenomena had been observed before in other astronauts before but not all of them. The thickening is likely related to being in microgravity, but scientists think that genetics are also part of the puzzle.

Genetics Need to be Considered


Both twins had genetic variations linked to the eye change, but only space-inhabiting Scott developed it. The other really interesting finding was that Scott’s telomeres - the ends of our DNA that protect our chromosomes - grew significantly longer when in space, But shrank after returning to earth, with some even staying smaller than they were before his departure. NASA scientists are particularly interested in how the stress of space life and the stress of returning to earth affects the long term health of its astronauts.

Overall the study will provide a lot of data for NASA to use to make sure astronauts receive the best care on future long-term missions. It could even provide some interesting ideas about how humans can improve their health on Earth.

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