Evaluating the scientific evidence to support mental health and well-being claims made on probiotic products.

Background: Increasing interest in probiotics for mental health has led to products marketed to consumers claiming psychological benefits. This study aimed to identify mental health claims on probiotic supplements and to provide a narrative review of the scientific evidence to support these claims.

Methods: Probiotic supplements with mental health claims on the product label were identified. A search of the scientific literature was performed using Google Scholar, PubMed and Cochrane Central Register of Controlled Trials. Studies were included if the primary outcome was mental health or a biomarker of mental health, if they investigated the exact probiotic strain or combination of strains as present in the product, and if the study was a trial of probiotics conducted in either humans or animals. Included studies were assessed for risk of bias.

Results: Fourteen probiotic products with mental health claims were identified containing five different strains or strain combinations. Eighteen studies relevant to the products and investigating mental health outcomes met inclusion criteria. Ten studies investigated the same combination of probiotics and provided evidence to support the claims made. Statistically significant results were not universally present for all products.

Conclusion: The amount and quality of evidence to support claims of mental health benefits made on probiotic products is variable. The results support the need for a grading system to facilitate informed consumer decision-making when choosing a probiotic supplement to support mental health.