Pilots, Astronauts, and the Aerospace Microbiota: A Narrative Review of Occupational Impact

The human microbiota plays a crucial role in maintaining health and preventing disease; however, the effects of occupational exposure on the microbiota of aircrew and astronauts are not fully understood. This narrative review aims to synthesize the current knowledge on microbiota alterations in aerospace medicine, assess the potential of probiotics as a countermeasure, and identify key gaps that warrant further research. The references were identified through searching PubMed for English articles published between 2010 and 2024, using keywords related to microbiota, probiotics, aviation, spaceflight, pilots, and astronauts. Additionally, the bibliographies of relevant papers were reviewed. Studies in aerospace medicine were selected based on their focus on the occupational impact on microbiota and the use of probiotics in this context. For aircrew, initial studies indicate a decrease in beneficial gut bacteria, suggesting that probiotics could enhance gastrointestinal health, immunity, and overall well-being. However, unsupervised use of probiotics carries potential risks. Conversely, spaceflight induces significant changes in the gut, skin, oral, and nasal microbiota of astronauts, characterized by altered diversity and abundance of specific microbial taxa. These changes include a relative decrease in the abundance of beneficial gut bacteria, an increase in opportunistic pathogens, and evidence of microbial transfer between astronauts and spacecraft surfaces. While simulated space studies suggest the potential for probiotics to mitigate dysbiosis, direct testing done during actual spaceflight is lacking. The observed microbiota changes during spaceflight are associated with various health implications, including alterations in metabolic pathways and interactions between the microbial metabolic capabilities and the host's metabolism. In conclusion, this review highlights the profound impact of spaceflight on astronaut microbiota and the promising role of probiotics as an intervention in both space and aviation medicine. However, significant research gaps remain. These include elucidating the functional implications of microbial shifts, developing personalized countermeasures, and validating the efficacy of probiotics during spaceflight. Future studies should leverage advanced tools such as metagenomic analysis and longitudinal tracking of astronaut health to inform targeted interventions that support the well-being of aerospace personnel. Integrating data across different sites of the body and missions, facilitated by resources like the Space Omics and Medical Atlas (SOMA), can help identify consistent microbial changes induced by the unique occupational conditions of spaceflight and aviation. This integrated approach will be crucial for developing effective microbiota-based countermeasures to mitigate the occupational health risks associated with space and aviation.