Human immune function and intestinal microbiota are suggested to be altered within long-duration stay in space. Accumulated evidences on earth support that Lacticaseibacillus paracasei strain Shirota (LcS) is a promising probiotic strain on improvement of immune function and intestinal microbiota. This study aims to investigate the impact of long-duration spaceflight as well as intake of LcS on the international space station (ISS), on immune system and intestinal microbiota in astronauts.

Inclusion Criteria:

• Individuals who are scheduled to stay on the ISS for at least 3 months
• Individuals who fully understand the study protocol and provide written informed consent for the study participation

Exclusion Criteria:

• Individuals who routinely use antibiotic, laxative, and/or bowel regulating medicine
• Individuals who participate in other research that competes with this study in terms of the purpose and field, e.g., study with dietary management or intake of bifidobacteria/lactic acid bacteria, oligosaccharides, antibiotic, laxative, and/or bowel regulating medicine