How A Year In Space Affected An Astronaut’s Genes4 min read

The long-await results of the study comparing twin astronaut brothers, Scott and Mark Kelly, were published in Science. The Twins Study produced some important findings on the effects long-term space travel may pose to a human body. In particular, changes in Scott Kelly’s genes during his time in space have been especially informative.

Expedition 45/46 Commander, Astronaut Scott Kelly along with his brother, former Astronaut Mark Kelly speak to news media outlets about Scott Kelly’s 1-year mission aboard the International Space Station. Photo Date: January 19, 2015. Location: Building 2. Photographer: Robert Markowitz

The Twin Study

The Twin Study was the most in-depth and comprehensive study of the impact of spaceflight on a human body to day. In 2015 Scott Kelly spent 340 days in space – the longest single stretch of time spent in space by any American. Not only that, but Mark Kelly, who was also an astronaut and Scott’s twin brother, functioned as a control on Earth for scientists conducting the study.

During the months prior, during and after Scott’s time in space, NASA scientists collected a range of samples from both brothers. This included blood, fecal and urine samples, to compare how spaceflight might affect the body.

Expected Findings

The high exposure to radiation in space, as a meant that some changes were expected.

“In a microgravity environment, like the one on the ISS, organs in the body are able to shift around, and that can affect the heart muscles in particular, including the way in which blood is pumped around the body,” says Leslie Kurtz, a blogger at and “Many astronauts have been diagnosed with cardiovascular disease after being out in space. We know heart disease can be a major risk for astronauts.” Similarly, eye damage has also been experienced by astronauts in the past, as the muscles in their eyes change due to the lower gravity.

During his mission, the blood supply to the back of Scott’s eye swelled and parts of his retina swelled, leading to problems with his vision. His carotid artery also thickened, which can be an indicator of cardiovascular disease in future.

The study also found that Scott suffered weight loss during his mission and showed some signs of dehydration. His immune system also experienced some major shifts whilst he was in space, but reassuringly, the flu vaccine still worked for him.

Changes To Gene Behavior and Telomeres

Exposure to radiation can cause strands of DNA to break and can move chromosomes around and cause them to swap places. This results in genes expressing themselves that might otherwise not, as well as causing other genes to stop expressing. Changes such as these can increase the chances of diseases, such as cancer.

Although Scott Kelly experienced some genetic changes during his time in space, about 91% had returned to normal, six months after he returned to Earth. Interestingly, most of the big shifts in Scott’s gene behavior happened in the latter half of his mission, which suggests that longer space trips could cause bigger changes to the body the longer an astronaut is in space.

The most surprising finding was what happened to the structure of Scott’s telomeres. “Telomeres are structures found at the end of chromosomes. Normally they are regarded as a biomarker of aging and by association, of age-related diseases,” explains Bea Martinez, a health writer at and “Telomeres shorten as we get older. The expectation was that Scott’s telomeres would shorten as a result of the unique stresses and environmental exposure he was under during his long mission. Instead, researchers found that during his spaceflight, Scott’s telomeres actually lengthened. Once he was back on Earth, however, they returned to their pre-flight level. In fact, about nine months after his return, researchers actually saw that Scott had more seriously shortened telomeres than he had had before.” 

Finally, changes to Scott’s cognition were also observed. During cognitive tests, he was unable to perform as well as he had both before and during his time in space. Researchers found that he was less accurate and slower than he had been previously.

Although the test sample in this study was too small to provide conclusive evidence, the data collected is extremely useful as NASA considers longer spaceflights. In order to fully understand the effects, both short-term and long-term, of long-duration spaceflight upon the human body, more research and data is required. Yet the research conducted on the Twin Study will undoubtedly help to design future missions.

Beatrice is a professional copywriter at and She specializes in a range of topics and likes sharing her personal experience at Beatrice enjoys giving advice to beginner writers and offering support helping them to create content, of all genres, that sells.


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