How does microgravity affect human gut bacteria during spaceflight? Information from the landmark NASA Twins study

The landmark NASA Twins study has found out the effects of microgravity on human gut bacteria during spaceflight, which may give valuable insights for future space travel to Mars.

The new research shows that extended spaceflight affects the human gut microbiome, possibly due to microgravity. The astronaut Scott Kelly and his identical twin brother, who is a retired astronaut, Mark Kelly, took part in the NASA Twins study over one year.

How astronaut Scott Kelly’s gut bacteria shifted during spaceflight

Scott Kelly was the first American astronaut to spend almost a year in space, from 2015 to 2016. During his stay on the International Space Station (ISS), he experienced a shift in the ratio of two major categories of bacteria in his gut microbiome. However, the diversity of bacteria in his microbiome, however, did not change during spaceflight, which the researchers believe to be an encouraging sign.

How microgravity affects gut bacteria

According to the team, a number of variables could have influenced Scott Kelly’s microbiome during spaceflight, including:

  • Microgravity;
  • Increased radiation;
  • Shifts in circadian rhythms;
  • Decreased sleep time;
  • Lack of air circulation;
  • The stress of living in an enclose space; and
  • An altered diet, consisting of mainly freeze-dried, irradiated and pre-packaged foods.

Northwestern’s Fred W. Turek, who led the study, commented: “We think that microgravity has an effect on the bacteria. That’s what we want to determine going forward.”

This is Scott Kelly at work on ISS maintenance with the station’s solar arrays visible in the background.
© Scott Kelly

Flying to Mars

Turek said: “We cannot send humans to Mars without knowing how spaceflight affects the body, including the microbes traveling with humans to Mars. And we need to know sooner rather than later. The plan is to send people to Mars in 2035, so we cannot wait until 2033 to gain this information.”

The significance of gut bacteria

Martha Vitaterna, the first author of the study and a research professor of neurobiology at Northwestern, explained: “The influence that bacteria have on all other systems of the body is really remarkable. There are studies that link changes in the gut microbiome with neurological and physiological conditions, like Alzheimer’s disease, Parkinson’s disease, autism and schizophrenia. By protecting the gut, we can protect all these other systems.”

The study found that “there was some kind of wholesale shift in remodeling of the structure of this community of microorganisms,” according to Vitaterna. She added: “We cannot say whether it’s good or bad.”

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