Travelling long distances can be tough on the body, and if it is on the Mars or Moon you are travelling to, it can take a serious toll on your overall health — body and mind included. It might look cool and fun to go on the space voyages in those fancy air-craft as we see in the movies, but in reality, they are excruciating, long and far from being fun.
Space-flight stressors affect the health of astronauts
According to NASA, there are five main hazards of human spaceflight: radiation, gravity, distance from Earth, hostile enclosed environments, and isolation. Spending time in the low gravity environment of space can cause significant changes to your body — your bones weaken and your sense of taste may reduce. Some of these stressors were even confirmed to alter the gut microbiota, representing a risk to astronaut health, especially during long-term spaceflight missions.
Gut microbial dysbiosis
The microbiota residing in our gut and its metabolic products are known to have an immense influence on our health and well-being — it not only trains our immune system but also controls our risks and severity of certain diseases/infections, our ability to respond to treatments and affect our emotions and mood.
Numerous factors including environmental stressors are known to disturb the balance among the gut microbial community (also known as dysbiosis). Dysbiosis is known to affect our immune system functioning, making us vulnerable to diseases and infections.
Being in a hostile microgravity environment can often cause nausea, and reduce the appetite of astronauts, which can, in turn, disrupt their gut microbiome. This can lead to malnourishment, making astronauts extra vulnerable to irritation and infections, and reduced immunity to fight diseases. It can also have an effect on their psychological health and cognitive skills.
During long-duration space missions, astronauts are known to suffer from a range of health issues ranging from gastrointestinal (GI) conditions (constipation and diarrhoea), respiratory illness, skin irritation and infections, bone and muscle loss as well as anxiety and depression. Many of these conditions coincide with the microbial dysbiosis, decline in immune function and concurrently increased inflammation.
I can’t even begin to imagine how astronauts might deal with the stinky situation of diarrhea. Forget diarrhea situation, NASA is still searching for effective systems for astronauts to poop into during space missions.
The Fecal Containment Device during the Apollo-era was essentially just a plastic bag that the astronauts strapped to their butts. Once they deposited their poop, the bags were either stored on the spacecraft or left on the lunar surface.
Fortunately, over the years, NASA and other space agencies have gotten better at handling the business of going to #2. Feces collected on the International Space Station (ISS) are sucked into a canister, which is then shot back towards Earth. (Apparently, it burns up in the atmosphere. Phew!!)
The dysbiosis in the microbiota and its associated effects on the health of astronauts has been a topic of intensive research. Scientists studying the impact of real or simulated microgravity conditions on commensal and opportunistic pathogenic bacteria suggested that space travel may cause functional changes in the crew microbiome, including bacterial virulence, antibiotic resistance, biofilm formation and growth. The samples collected before and after space flights from astronauts have also identified shifts in the microbial composition of the oral, nasal and intestinal microbiota.
More recently, researchers studied the impact of long-term space exploration on the microbiome of nine astronauts who spent six to twelve months on the International Space Station (ISS) and confirmed substantial alterations in the composition of the astronauts’ microbiome during space travel. The ISS is a modular space station (habitable artificial satellite) in low Earth orbit.
The composition of the intestinal microbiota became more similar across crew members in space. There is also an indication of the decline in bacterial groups with anti-inflammatory potential, some of which were also correlated with changes in the pro-inflammatory cytokine (increased inflammatory signalling molecules) profile of ISS crewmembers. A bloom of a few bacterial types was also consistently observed in these astronauts.
Specifics of microbial dysbiosis :
- Among the bacterial groups in intestinal samples, there was a more than 5-fold inflight reduction in Akkermansia and Ruminococcus, and a 3-fold drop in Pseudobutyrivibrio and Fusicatenibacter. Most of these compositional changes resumed to preflight levels after astronauts returned to Earth, with the exemption of two genera of the phylum Firmicutes.
- The skin microbial communities whose abundance dropped while in space were mostly Gram-negative Proteobacteria with a predominance of Gamma- and Beta-proteobacteria (Moraxella, Pseudomonas and Acinetobacter). In contrast, most of the skin bacteria that became more abundant inflight belonged to the phylum Firmicutes, Bacteroidetes and Actinobacteria, including bacteria of the genus Streptococcus, Staphylococcus and Corynebacterium. Compared to preflight skin, postflight samples showed a similar trend as inflight samples (lower Proteobacteria and higher Firmicutes, Bacteroidetes and Actinobacteria).
- The microbiota of the nose also showed a similar trend but milder response to the space environment with a significant decline in two genera of Gram-negative bacteria that were also reduced in skin. Many of the observed changes in the nasal microbiota were restored after the astronauts returned to Earth, with higher abundance of Bifidobacterium and Akkermansia, and lower levels of Pseudoalteromonas in postflight samples.
While it is not clear if the observed changes in the GI microbiome during spaceflight pose a risk to astronauts’ health, it certainly offers some pointers that need attention.
- An inflight bloom in Streptococcus, Staphylococcus and Corynebacterium — the virulence characteristics of these bacterial species need further investigation to appreciate their potential risk to astronauts’ health during long-duration space missions.
- A space-associated increase in the relative abundance of Proteobacteria Parasutterella — the bacterium that has been positively associated with chronic intestinal inflammation in patients with irritable bowel syndrome (IBS).
- A space-associated reduction in the relative abundance of intestinal Fusicatenibacter, Pseudobutyvibrio and Akkermansia — these three bacterial genera are associated with anti-inflammatory properties and their decline is reported in many chronic health conditions.
- Akkermansia, a probiotic, is a short-chain fatty acid (SCFA) producer in the intestine, which contributes to the integrity of the gut epithelium and reduces the intestinal inflammatory response.
- The levels of intestinal Fusicatenibacter negatively correlated with the concentration of pro-inflammatory cytokines IL-8 and IL-1b, which were slightly but significantly increased in space. This supports the influence of microbiota changes on immune system activities.
Alteration in the genes and cognitive functions
As with the faltering immune system during the space missions, there is a potential to cause changes in genes, some of which are long-lasting. The NASA Twins Study found that space travel in an astronaut, Scott Kelly, on a year-long mission caused lasting changes to 9% of his genes (91% changes reverting back to normal on his return to Earth). The study compared his DNA to that of his identical twin brother, Mark Kelly, who remained on Earth.
The alterations in the gene expression observed in Scott were also associated with other findings in the Twin Study — including the body’s response to DNA damage, telomere regulation, bone formation and immune system stress. While Scott’s cognitive performance (such as mental alertness, spatial orientation, recognition of emotions) remained largely unaffected during his time in space, a marked decline in his speed and accuracy was observed after his landing on Earth that persisted for six-months.
The microbial analysis of the Twin Study also helped appreciate the effect that diet and confinement can have on the intestinal microbial community during space voyages. Scott’s gut flora was found to be markedly different during flight versus preflight. While the Bacteroides abundance spiked, consistent with simulated space environment tests, the populations of probiotic Lactobacillus and Bifidobacterium decreased, possibly affecting Scott’s immune function.
While the influence of other space-specific environmental factors on these changes cannot be overlooked, the food he consumed (mainly freeze-dried or thermo-stabilized prepackaged food) while on the space station is thought to account for the majority of these microbial alterations. On his return back to Earth, Scott’s microbiome returned to its preflight state.
Therefore, food, that is a significant modifiable factor of the gut microbiota needs special attention when feeding astronauts on longer space missions to countermeasure the health issues associated with spaceflight.
Foods in space
Foods taken into space must have specific properties — they must be light-weight, compact, tasty and nutritious. They must also keep for long periods without refrigeration. A variety of menus consisting of foods (meals and snacks) are provided to each astronaut with 2500 or more calories per day.
Foods chosen for the daily menu are selected based on their commonality to everyday eating, their nutritional content and their applicability to use in space. Most food for space-application is preserved through a process known as freeze-drying.
Prior to packaging, food is quick-frozen and then placed into a vacuum chamber. The vacuum removes all moisture from the food. They are then packaged while still in the vacuum chamber. Freeze-drying provides foods that will preserve their nutrition and taste qualities almost indefinitely. They are extremely light and compact and require no refrigeration.
Preparation differs based on the food type. Some foods can be eaten in their natural forms, such as brownies and fruit. Other foods require adding water, such as macaroni and cheese or spaghetti. The oven is used for warming foods to the proper serving temperature in space. There are no refrigerators in space, so space food must be stored and prepared properly to avoid spoilage, especially on longer missions.
Unlike previous space vehicles intended for astronauts, Skylab had a freezer and refrigerator, a convenience no other vehicle offered. The Daily Menu food supply is based on the types of food storage conditions:
- Frozen — most entrees, vegetable, and dessert items
- Refrigerated — fresh and fresh-treated fruits and vegetables, extended shelf-life refrigerated foods, and dairy products
- Ambient — thermostabilized, aseptic-fill, shelf-stable natural form foods, and rehydratable beverages
The countermeasures based on prebiotic and probiotics supplements are being intensively researched for their suitability and effectiveness in astronauts during long-term space missions. However, this area is still in its infancy and many questions remain to be answered — particularly, regarding the persistence of the efficacy of probiotics and/or prebiotics under microgravity conditions.
The efficacy of prebiotic fibre to produce anti-inflammatory SCFAs will be dependent on the status of the astronaut’s microbiome (presence/types/levels of fibre fermenters). Precision microbiome modulation with discrete dietary prebiotic fiber structures that promote the production of SCFAs with anti-inflammatory potential may be of significant benefit to future space missions.
The constraints and risks of spaceflight make it imperative that probiotics are carefully selected based on their strain-specific benefits, doses, delivery mechanisms, and relevance to likely crew conditions prior to evaluation in astronauts.
The delivery of probiotics in food in space also poses significant challenges. No fermented foods or probiotic foods are currently allowed on the astronaut food system due to strict microbiological controls and lack of refrigeration on most spaceships.
Once the best bacterial strains and prebiotic fibres are identified, selected and tested rigorously in intervention studies in space travellers, the best approach would be to combine prebiotic and probiotic to augment the health benefits in astronauts.
The countermeasures designed to alleviate health issues related to the long-term space voyages should also consider gender-specific differences in micro-gravity environments. Men and women are known to respond differently in the zero-gravity conditions.
Unlike the astronauts who are limited by their choice of foods they can eat during space missions, we, on Earth are not limited by the access to a variety of options for nutritious foods. Do not underestimate this simple yet important privilege available to us on this beautiful planet Earth.
While the astronauts can hope to regain most of their health functions once they return to the Earth, you and I, my friend, do not have that choice. We can’t return to Earth while we’re already on the Earth. So take care of your gut and it will take care of you.
If you want to know more about the nutritional strategies to nourish your gut health, you are welcome to read my article below that might guide you to make the right choices: