Probiotic Research: Open-label Functional Intervention and Longitudinal Evaluation in Healthy Adults

• Probiotic Supplementation (Lactobacillus plantarum) (Dietary supplement): This probiotic is a proprietary food-grade supplement that is not yet commercially available or CE-marked.

Primary outcomes

• Changes in metagenome of stool samples [From enrolment to the end of treatment at 4 or 24 weeks respectively. Optionally, a follow-up measure may be offered 24 weeks after the end of treatment.]: The investigators will evaluate changes in genetic material in participant stool, representing establishment of the probiotic in the digestive tract

Secondary outcomes

• Change in blood multiome [From enrolment to the end of treatment at 4 or 24 weeks respectively. Optionally, a follow-up measure may be offered 24 weeks after the end of treatment.]: This measure will evaluate change in blood proteins (plasma proteome) and blood metabolites (plasma metabolome). Both measures are quantified using mass to charge ratio.
• Changes in cognition [Assessed weekly from enrolment and to end of treatment at 4 or 24 weeks respectively.]: Participants will complete a weekly online cognitive test administered via our remote platform. This generates a score relativised to each participant's performance, and does not utilise a scale.
• Change in daytime sleepiness [Assessed at enrolment and at end of treatment at 4 or 24 weeks respectively.]: Participants will complete the Epworth Sleepiness Scale (ESS), with a minimum score of 0, and a maximum score of 24. A higher score indicates worse daytime sleepiness.
• Change in sleep quality [Assessed at enrolment and at end of treatment at 4 or 24 weeks respectively.]: Participants will complete the Pittsburgh Sleep Quality Index (PSQI) survey. This has a minimum global score of 0, and a maximum of 21. A higher score indicates worse sleep quality.
• Change in self-reported wellbeing and mood [Assessed at enrolment and at end of treatment at 4 or 24 weeks respectively.]: Participants will fill out a questionnaire at the beginning and end of the study which will ask questions about subjective mood and wellbeing.
• Adverse event monitoring [Assessed from enrolment until end of treatment at 4 or 24 weeks respectively.]: Participants will be expected to self-report any adverse features resulting from use of the supplement

Sex: All, ages: 18 Years to any, accepts healthy volunteers

Inclusion Criteria:

* Aged 18 years or older at the time of providing informed consent.
* In generally good health, with no known medical conditions that could interfere with the aims of the study or participant safety, as judged by self-report and screening questionnaire.
* No history of significant psychiatric or neurological illness
* Ability to complete study specific tasks, including:
* Daily oral intake of a probiotic capsule
* Self-collection of stool samples
* Completion of online questionnaires and simple cognitive tasks
* Able to read, understand, and communicate in English, in order to give informed consent and follow study instructions.
* Access to the internet and a suitable device (e.g., smartphone, tablet, or computer) for completing online aspects of the study.

Exclusion Criteria:

* Participants will be excluded from the study if any of the following criteria apply:
* Use of any systemic antibiotic or systemic immunosuppressive medication within the past 8 weeks, including but not limited to:
* β-lactam antibiotics, macrolides, tetracyclines, fluoroquinolones, aminoglycosides, glycopeptides, sulfonamides, antimycobacterial agents, systemic antifungals or antivirals
* Use of any systemic immunosuppressants within the past 16 weeks, including, but not limited to:
* Systemic corticosteroids, conventional immunosuppressants, biologic immunomodulators, targeted synthetic immunosuppressants, cytotoxic chemotherapy, or transplant-related immunosuppression.
* A longer exclusion window is applied for systemic immunosuppressive therapies due to their prolonged and potentially lasting effects on immune function and gut microbial composition compared with systemic antibiotics.
* Participants who commence systemic antibiotics or immunosuppressive therapy after enrolment will not be withdrawn from safety monitoring but will stop the supplement and will not continue the intervention phase of the study. With participant consent, data collected may still be used.
* Major gastrointestinal disease or surgery:
* Any history of significant gastrointestinal disease or surgery that may alter gut microbiome composition, immune function, or nutrient absorption, including but not limited to inflammatory bowel disease (Crohn's disease, ulcerative colitis, indeterminate colitis); coeliac disease or other chronic malabsorptive disorders; chronic liver, biliary, or pancreatic disease; moderate-to-severe or unstable irritable bowel syndrome; gastrointestinal malignancy; chronic gastrointestinal motility disorders; recurrent Clostridioides difficile infection; or any major gastrointestinal surgery such as bowel resection, bariatric surgery, colectomy, ileostomy or colostomy. Prior appendectomy or cholecystectomy alone is not exclusionary.
* Current pregnancy or development of pregnancy, breastfeeding
* Known allergy to probiotic or compounding ingredients:
* Vitamin D3
* Isomaltooligosaccharide
* Yeast extract