Space travel subjects astronauts to a harsh environment. Microgravity, cosmic radiation, confinement, and other challenges lead to many health risks. Disorders may include reduced immunity, increased infections of the genitourinary tract, reactivation of viruses, bacterial resistance, cardiovascular issues, cancers, cognitive decline, bone loss, muscle atrophy, and mental health concerns.
Dysbiotic changes in the gut, nose, and skin microbiomes induced by space travel are involved in many of these health concerns. Researchers suggest that the microbiota of the gut and other areas may be novel targets for combatting some of these changes in space travelers. Probiotics may counteract some of the detrimental effects.
This blog takes a look at the current evidence regarding the potential use of probiotics in space travel.
Space travel and physiological challenges
Traveling in a closed environment thousands of miles from earth exposes astronauts to stressors that can lead to a substantial spate of health issues. As manned missions extend for longer durations and farther reaches, it is even more imperative to address the harmful physiological impacts of space travel.
What may initially look like harmless fun, the weightlessness experienced when freed from the earth’s gravitational pull can have dire effects on multiple body systems, including neuro vestibular, cardiovascular, musculoskeletal, bone metabolism, and immune-hematological systems. Immediate adaptation to microgravity causes fluid shifts, increased pressures, reduced leg volume, potential ocular damage, and altered gut function. Most space travelers also experience motion sickness, affecting the performance of 60-80% of astronauts and resulting in reduced energy intake, decreased gastric activity, and delayed gastric emptying.
Cosmic radiation results in epigenetic changes and high levels of oxidative damage and tissue inflammation. The oxidative stress of cosmic ray exposure is associated with the etiology of several human diseases, including cancer, cardiovascular and neurodegenerative disorders, gastrointestinal diseases, and notably many diseases related to aging.
Prolonged separation from society in a confined environment can lead to psychological stressors such as homesickness, loneliness, interpersonal conflicts, and reduced mental well-being. Factors such as constricted living space, external hazards, radiation exposure, and dietary changes further contribute to stress, impacting sleep patterns, physical health, and crew relationships.
Disrupted circadian rhythms
Disrupted and short sleep durations are seen in space flights. Compromised sleep can result in persistent, widespread low-level inflammation and is linked to several diseases characterized by inflammation. The immune system is altered by sleep deprivation, which can lead to an increased risk of infection. In addition, the close proximity inside the space capsule can promote the spread of infection.
Microbiota changes in space travel
Exposure to stressors in space can alter the stability and composition of the gut, nasal, and oral microbiota.
Research conducted on mice and humans during space missions has revealed changes in the gut microbiome, including alterations in community structure, increased abundance of certain bacteria, and a decrease in beneficial bacteria.
Mice flown on several real space missions demonstrated a higher abundance of Clostridiales and fewer Lactobacillales. In one of these, mice flown for 37 days onboard the International Space Station demonstrated “unchanged richness of microbial community, an altered community structure, and an elevated Firmicutes-to-Bacteroidetes ratio.”
An investigation of the microbiota from nine astronauts who spent 6-12 months aboard the International Space Station observed changes in the microbial population of the gut, nose, tongue, and skin. For example, increases of Parasutterella (associated with chronic intestinal inflammation) and reduced proportions of several genera with anti-inflammatory properties, such as Akkermansia, were observed in the gut microbiome during space flight.
Another notable study called the Twins Study compared the gut microbiomes of an astronaut and his identical twin on Earth, showing transient changes in the microbiome (an increase in the Firmicutes-to-Bacteroidetes ratio) in the twin during spaceflight, which returned to pre-flight levels upon return to Earth. In addition, anti-inflammatory metabolites, such as 3-indole propionic acid, were noted at low levels in flight.
Alterations in the composition and functionality of the gut microbiome can be induced even by short-term space travel. One study reported shifts between dominant genera in the microbiome during space missions of 15 and 35 days that led to an increased abundance of Bacteroides.
The effect of microgravity on the gut microbiota of astronauts during spaceflight is summarized here.
Marked fluctuations were also documented in a simulated spaceflight study conducted on humans. Simulated microgravity on the ground using a hindlimb unloading mouse model caused a decrease in bacterial genera associated with anti-inflammatory properties, gut homeostasis, and health benefits such as kidney stone prevention.
Similar to what is observed in the gut microbiome, the skin, oropharyngeal, and nasal microbiomes during space flight show variations in diversity and abundance of certain bacterial genera, which may contribute to skin hypersensitivity reactions, rashes, and respiratory symptoms. Disruptions in the microbiota of these areas can increase susceptibility to infection and the overgrowth of pathogens.
See a list of microbiome studies pertaining to spaceflight as well as ground-based simulations (conducted through 2021).
As mentioned before, changes to gut microbiome composition appear to be reversible following return to earth, however, persistent microbial changes with extended exploration missions may have long-lasting implications.
Impact of spaceflight-induced microbiome alterations
The impact of spaceflight conditions on microbial physiology and host-microbe interactions has been explored. Studies show changes in bacterial growth kinetics, increased mutation rates, altered gene expression and virulence factors, antibiotic resistance, enhanced biofilm formation, increased horizontal gene transfer, and potential risks of antibiotic resistance and pathogenicity.
According to a recent review, gut microbiota, influenced by the brain and environmental factors, plays a crucial role in the mental health of astronauts during spaceflight. Astronauts also face challenges related to genitourinary tract infections, virus reactivation, bacterial resistance, epithelial barrier disruption, immunological alteration, cardiovascular functions, and the effects of cosmic radiation.
Support for probiotics use in space flights
- Inhibition of pathogen binding to the intestinal epithelial layer by altering mucus secretion and competing for adhesion sites, while also improving the integrity of the intestinal barrier.
- Modulation of the immune system by altering cytokine secretion and strengthening the gut barrier.
- Exhibition of antimicrobial activity through the synthesis of organic acids and bacteriocins.
- Potential benefits in treating intestinal disorders, preventing antibiotic-associated diarrhea, reducing the risk of cancer, alleviating stress and anxiety, and preventing urinary tract infections.
- Production of short-chain fatty acids, which play a vital role in immune regulation and maintaining gut health.
Given the acknowledged advantages of probiotics in promoting a healthy gut microbiome and overall well-being, utilizing them in space travel, whether by incorporating them into food or using them as supplements, shows great potential as a viable solution to mitigate the dysregulation and health challenges faced by astronauts.
Researchers believe that promising probiotic candidates for space missions could include Bifidobacterium and Lactobacillus, to counteract their decrease in relative abundance in the astronaut microbiome during spaceflight.
Nevertheless, uncertainties remain regarding the viability of probiotics in microgravity environments. Several studies have investigated the effects of microgravity on probiotics.
- One study found that simulated microgravity conditions had positive effects on Lactobacillus acidophilus, such as increased tolerance to acid and bile, enhanced antimicrobial activity, and maintained adherence ability.
- Another study using Limosilactobacillus reuteri revealed increased tolerance to the gastrointestinal passage and enhanced production of the bioactive compound reuterin.
- Additionally, a study on three commercial probiotics showed that only Bacillus subtilis spores could survive the conditions simulating the passage through the gastrointestinal tract, suggesting that spore-based probiotics may be suitable for long-term space travel.
The findings presented here are based on small numbers and should therefore be interpreted with caution. Nevertheless, understanding the changes in the microbiome during space travel is important for managing the considerable health risks associated with space flight. While these changes can be reversible, prolonged periods of space travel may result in enduring effects.
Probiotics have the potential to serve as countermeasures to alleviate these risks. Once the most suitable bacterial strains are identified and selected, intervention studies should be undertaken on astronauts to validate their potential effectiveness during space missions.
Prebiotics and postbiotics are also candidates for further study.
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