- As the space race heats up, keeping astronauts healthy on long missions is a major obstacle
- One review argues that ensuring a healthy gut is key to protection against disease in space
- This means incorporating targeted pre- and probiotics in a fibre-rich diet for space travellers
To infinity and beyond – or, as far as our fragile human bodies can take us.
As the space race is reignited by billionaires who want to take people to Mars, we have to start thinking about how astronauts' health will be affected by such long space missions.
According to research published in Frontiers in Physiology, our gut microbiomes could be the key to ensuring we stay healthy on missions to the moon, Mars and beyond, and rehabilitate our systems once back on Earth.
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Gut in space
What do we know about the gut and space flight? Astronauts on the International Space Station (ISS) don't consume the same nutrients while on spaceflights as they would on Earth, taking in less fluids, expending more energy than consumed, while experiencing lower gastrointestinal transit time. This can impact muscles, the heart, immune function and cognition.
Zero- or microgravity also has an impact as the body adapts to its new environment, shifting fluids from the bottom of the body to the top. Other elements of space flight that affect the gut include changes in sleep, galactic radiation, medication and just general stress.
"Since the early 1960s, some of these stressors have been shown in both animal and human studies to promote gut microbiota dysbiosis, which may drive gastrointestinal disease and metabolic imbalances, as well as changes in bacterial physiology in the spaceflight environment and ground-based analogue studies," write the researchers.
The top three medical events that took place in space were space adaptation syndrome, neurosensory alterations and gastrointestinal problems.
These effects are easily fixed on short-term flights, like to the ISS, but impaired health could seriously jeopardise future space flights of a year or longer.
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Improving the space diet
Scientists have been working for a long time on ways to improve the astronauts' diets for physiological fitness in microgravity environments. If you can fix this, gut microbes that depend on proper nutrition might also better adjust to the extreme conditions.
It's been proven time and time again that a healthy gut is a healthy you, and the researchers suggest that pre- and probiotics should form part of the countermeasures implemented to protect an astronaut's health.
They can maintain the richness (numbers of bacteria) and diversity (number of bacterial species) of the astronauts' gut microbiota to keep them similar to what they were on Earth.
"Problems to which the gastrointestinal tract is particularly prone are infection and inflammation. In this context, the gut microbiome may play a critical role in being able to exert a barrier effect against potential enteropathogens, promote the integrity of the epithelial barrier, and influence immune function."
Existing studies limited
However, studies on the gut microbiota of astronauts are still very small and limited, so there's a lot of speculation in the field. Studies involved mice, which showed the richness of the gut microbiota stayed the same while the community structure changed, and the famous twin astronauts study that showed similar results.
In both studies, there was also an increase in the Firmicutes-to-Bacteroidetes ratio, a relationship between two types of gut bacteria that changes as we age, while diversity remained unchanged in the twins study.
The most important study was the Astronauts’ Microbiome project, which took samples from nine astronauts prior to launch and then again after their six-month or one-year missions. They found that their microbiota did change in microgravity and that their colonies became very similar to those of their colleagues on the space station.
But they couldn't determine whether or not this had an impact on their health, although they did find that inflammatory-linked bacteria increased while anti-inflammatory bacteria decreased. They could trigger inflammatory diseases, so a probiotic with the right strains might be able to combat this.
There's also some evidence that good gut microbiota could help fight the loss of bone mass that happens in space, which could be incorporated in probiotics. The science is still out on whether this could benefit muscle mass, though it might help muscle function and strength.
The gut's bidirectional link to the brain is another important factor to consider, as neurological decline in astronauts on long space flights has serious effects on a mission's success. Ensuring the gut is happy will keep the brain more resilient against external stressors.
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Fibre remains important
"More recently, ground-based space simulations have provided intriguing (although not entirely unequivocal) insights into the possibility of maintaining a eubiotic gut microbiome layout (poor in potential pathobionts while rich in health-promoting [short-chain fatty acids] producers) through a bioregenerative life-support system – a confined, self-sustained artificial ecosystem to biologically regenerate O2, food, water and other basic living necessities."
While the results from these simulations will differ from real space situations, it does highlight the importance of well-defined dietary guidelines with high fibre intake. Because people's gut microbiota differ widely, personalised diets for astronauts could also be beneficial in addressing each individual's nutritional needs.
"In humans, it is commonly accepted that a healthy and balanced diet, with a regular intake of dietary fibre through fruits and vegetables, allows the prevention of several diseases resulting from immune deficiencies such as cancer, and a better immune response against pathogens.
"In view of the effects on immunity, the use of prebiotics and probiotics to stimulate the production of [short-chain fatty acids] would thus increase nutrient and metabolic resources and the eliminatory capacity of lymphocytes, which may limit the re-emission of latent viruses."
More research into microgravity environments with pre- and probiotics and fibre-rich diets is still much needed to figure out the best strains and methods to improve resilient gut microbiota in the depths of space.
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