Science & Technology

The NASA twin study shows the effects of space travel

The one-year NASA study involving twin brothers reveals the effects of spaceflight on the human body more comprehensively than ever before.
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The one-year NASA study involving twin brothers reveals the effects of spaceflight on the human body more comprehensively than ever before.

In an unprecedented year-long project, astronaut Scott Kelly spent 342 days in space, whilst his twin brother, Mark, remained on earth. The aim: to assess the effects of spaceflight on the human body.

Scott Kelly at work on ISS maintenance with the station’s solar arrays visible in the background (NASA)

The groundbreaking NASA study brought together 84 researchers from ten separate research teams, across 12 universities to create the most comprehensive study of the effects of space travel on the human body.

The research investigated physical traits such as cardiovascular health, protein regulation, ocular degeneration and cognition, right down to a genetic level — even examining the effects on Scott’s gut bacteria and his telomeres — the ‘caps’ that prevent chromosomes from ‘fraying’.

The results begin to fill in gaps about potential health consequences for astronauts who remain in space for longer than six months, and the effects of associated hazards such as exposure to radiation and microgravity. 

Thus far, the way these risks impact health during extended stays in space has been unclear, however. Francine Garrett-Bakelman and colleagues leveraged the opportunity to study this when Scott Kelly spent a year in space aboard the International Space Station (ISS) between 2015 and 2016. Meanwhile, his brother, Mark Kelly, a former astronaut himself, remained on Earth as a ground control. 

After a year, samples from the twins were compared to see the possible effects of spaceflight.

Steve Platts, PhD, deputy chief scientist at the NASA Human Research Program, says: “The Twins Study provided the most comprehensive and integrated molecular view to date of how a human responds to spaceflight. 

“Results will help expand our understanding of the physiological and psychological adaptations to space.”

The researchers discovered that there were no long-lasting major ill-effects on Scott’s body despite him spending almost a year orbiting at 400 km above his brother. They also discovered that many of the changes that did occur to Scott’s body returned to normal six months after his return to Earth.

Andrew Feinberg and Lindsay Rizzardi test procedures for purifying blood samples on NASA’s microgravity plane called the ‘Vomit Comet.’ (John Hopkins) 

As Jenn Fogarty, PhD, chief scientist at the project, points out: “ “The Twins Study demonstrated on the molecular level the resilience and robustness of how one human body adapted to the spaceflight environment. 

“This study was a stepping stone to future biological space research focusing on molecular changes and how they may predict health and performance of astronauts.”

Scientists collected blood samples, physiological data and cognitive measurements from Scott and Mark Kelly at various time points over 27 months before, during and after Scott’s one-year space mission. The samples from Scott during the flight were collected on the space station when shipments from Earth arrived on a Soyuz rocket and, that same day, shipped back to Earth on the rocket so that the samples could be processed within 48 hours.

Scott Kelly’s personal living quarters on the ISS (NASA)

As Brinda Rana, PhD at UC San Diego School of Medicine, points out, even this had to be an operation of extraordinary precision: “ Blood volume drops in space and the astronauts are chronically dehydrated. These factors add to the difficulty of obtaining samples in space.

“The challenge was to collect enough biofluids onboard the ISS at multiple time points throughout the year for all 10 investigative teams to conduct this comprehensive omics view of the human body in space.”

These challenges have also highlighted the need for NASA to develop methods that allow astronauts to perform gene-sequencing ‘on the -go’ and may lead to exciting new research into portable DNA sequencing tools. 

Why twins?

Identical twin brothers: retired astronaut Mark Kelly (left) and Scott Kelly ( NASA/ Robert Markowitz)

The twin study provided NASA with a unique opportunity to use Scott’s twin brother, Mark, as a baseline control here on Earth.

With Mark and Scott being so genetically similar, researchers were able to sift out changes that occurred to Scott as a result of his exposure to space travel from any changes that may have occurred naturally to the twins as a result of their genome.

Dr Christopher Mason, an associate professor of physiology and biophysics at Weill Cornell Medicine, says: “It is likely that these two astronauts have been studied at a greater depth than any other person in history.

 “They give us a really in-depth view of cellular, molecular and physiological changes that can help us learn what is in the range of what a human can endure.”

The study should be viewed with caution

It should be noted, that due to the rarity of twin astronauts, the study has an extremely small sample size. As Andrew Feinberg, M.D., the Bloomberg Distinguished Professor of Medicine, Biomedical Engineering and Mental Health at The Johns Hopkins University, warns: “Since we only have two people in our study, we can’t say that these changes are due to space travel itself.

 “We need more studies of astronauts to draw such conclusions.”

In addition to this, as the ISS is in a low-Earth orbit it means that Scott was not exposed to the levels of radiation that an astronaut on a trip to the Moon or Mars would experience.

The results, despite not being completely conclusive, point towards areas of interest that will be to be focused on if humanity is to embark on longer space missions — particularly a 2–3-year mission to Mars.

Markus Löbrich writes in relation to the study in Science : “Undoubtedly, the study by Garrett-Bakelman et al. represents more than one small step for mankind in this endeavour.”

Key areas of research included

  • Heart and ocular health
  • Effect on gut bacteria and health
  • The effectiveness of vaccines for astronauts
  • Changes in the length of Scott’s telomeres — caps on chromosomes which scientists believe are responsible for ageing and ageing-related illness. 
  • Effect on cell mitochondria 

Key findings from the research

  • Scott experienced dramatic shifts in telomere length dynamics, a biomarker that can help evaluate health and potential long-term risks of spaceflight. 
  • Scott experienced thickening of the carotid artery, thickening of the retina, and weight loss. As well as a reduction in cognitive abilities. 
  • There was some DNA damage: 91.3% of Scott’s gene expression levels returned to normal or baseline levels within six months of landing back on Earth. About 7% of gene expression changes persisted after six months on Earth.
  • the flu vaccine administered in space worked exactly the same as on Earth
  • changes in Scott’s diversity of gut flora in space were no greater than stress-related changes scientists observe on Earth
  • proper nutrition and exercise while in space resulted in decreased body mass and increased folic acid, which is vital for making red blood cells, for Scott.
  • The majority of radical changes in gene expression occurred during the latter six months of the space mission rather than the first six month period.
  • NASA attributed most of the key findings and effects to the stresses placed on the human body by spaceflight rather than an external effect such as exposure to radiation. 
  • NASA states: “Given that the majority of the biological and human health variables remained stable, or returned to baseline, these data suggest that human health can be mostly sustained over this duration of spaceflight.”

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