Effect of a Dietary Supplement Versus Placebo on Serum PFAS Levels in Male Firefighters

This study is designed to evaluate the effect of a probiotic dietary supplement containing Streptococcus salivarius on serum PFAS levels in male firefighters with documented occupational PFAS exposure, following twice-daily use over a 12-week period.

Inclusion Criteria: * Able to give written informed consent * Male firefighter with previous career exposure to PFAS * BMI between 18.5 and 35 kg/m² * Serum PFOS level ≥5 ng/mL at screening * Willing to consume the study product daily for the duration of the study Exclusion Criteria: * History of drug and/or alcohol abuse (\>15 standard drinks per week) * Food allergy, intolerance or dietary restriction that, in the opinion of the investigator, would preclude consumption of the study product * Blood donation within the past 3 months * Current smoker of \>20 cigarettes per day, or former smoker with a history of ≥20 cigarettes per day who quit within 6 months prior to Visit 1 * Any significant acute or chronic health condition that would prevent participation, pose a risk, or confound interpretation of results, including: diagnosed gastrointestinal disorders (irritable bowel syndrome, inflammatory bowel disease, Crohn's disease, ulcerative colitis, coeliac disease, or other chronic diarrhoeal disorders); uncontrolled medical conditions; history of chronic kidney or liver disease; chronic inflammatory or autoimmune disease; history of gastrointestinal surgery; hospitalisation within the past 3 months * Current or recent (past 12 weeks) use of medications affecting bile acid metabolism (e.g. bile acid sequestrants, fibrates) or antibiotics * Current or recent (past 4 weeks) use of supplements affecting gut microbiota (prebiotics, probiotics, postbiotics, fibres, synbiotics), detoxification pathways (milk thistle, N-acetylcysteine, glutathione) or bile acid metabolism (e.g. psyllium husk) * Current or recent (past 2 weeks) consumption of prohibited foods, including probiotic yoghurts * Considered by the investigator unlikely to comply with study requirements * Current participation in another clinical study, or insufficient time elapsed since a previous experimental study