The Health Perils of Going Intergalactic

by Kristina C. - May 1, 2017

Liubov Edwards for
Liubov Edwards for

Spending a year in space—who hasn’t imagined it? The view of a blue-green marbled Earth out the spaceship window, eating freeze-dried ice cream out of a pouch, and gliding from place to place without touching the floor. Sounds a little more exciting than a normal holiday.

“Now, at last, space travel is open to all of us,” says the website of Richard Branson's Virgin Galactic—a company planning to offer commercial space flight to tourists with the goal of “democratizing access to space for the benefit of life on earth”.

But how much would you pay for a trip to space? Would you pay with your health?

The truth that’s not often acknowledged by people like Branson is that outer space is extremely hard on the human body. Sleep deprivation, psychological stress, microgravity, and cosmic radiation are a necessary part of space travel. They contribute to the poor health of astronauts, and are some of the reasons why they tend to have compromised immune systems and suffer permanent changes in their cardiovascular systems and eye health.

Scientists studying the effects of space travel on physical health have an urgent task ahead: to figure out the risks of both short-term and long-term experiences in outer space so they can protect professional astronauts and space tourists alike.

NASA reported recently that these scientists have added a new dimension to their analyses: the human microbiome. This collection of microorganisms that live in and on the human body are linked to many aspects of health, and have an especially close relationship with the immune system. Changes to the species of microbes that live on the body—especially in the intestines—can be tracked for insights about health, but the microbes are not so easy to study because they vary so much from person to person. Genes, diet, living environment, and a host of other factors influence which bugs live inside a person’s gut.

Two American brothers who both became astronauts gave scientists a great opportunity to study health changes in space through the microbiome. Because the brothers, Mark and Scott Kelly, are identical twins, the scientists were fortuitously able to keep one important factor constant—their genes. Between 2015 and 2016, Scott spent 342 days on the International Space Station while Mark remained on Earth. Analysis of their gut microbiomes (through fecal samples) showed that Scott experienced a major shift in his gut microbiome during his time in space, especially when it came to the ratio of two important bacterial groups (phyla) in the gut, Firmicutes and Bacteroidetes. Mark, on the other hand, had only minor gut microbiome fluctuations during the same period. And when Scott came back to Earth, his baseline gut microbiome returned.

Some aspect of space was messing with Scott’s microbiome, but it’s not clear what. A prime contender would be his diet, but many other factors could have played a part. A key question to answer is whether this shift was related to the health effects that Scott and other astronauts typically experience.

One concerning point for scientists is the lack of exposure to microbes while in space. From sterile food to filtered air, astronauts are exposed to only a fraction of microbes that they encounter while on Earth. This helps minimize infections during space travel, but it might also negatively impact their health, as constant exposure to a healthy complement of microbes from the outside environment is proving to be important for immune system homeostasis. Probiotics—bacteria with a health benefits—might be a good solution to this problem, but scientists would first need to hone in on which strains and doses would really give the astronauts a leg up on their health.

Much has yet to be learned about how the human body fares in space. But let’s hope the 700 "future astronauts" from 50 countries who have already paid deposits for space flights on Virgin Galactic are paying attention: before you go cosmic, consider your microbes and your health.


Kristina Campbell is a freelance science writer specializing in the gut microbiota and digestive health.

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