Biological activities of kombucha beverages: The need of clinical evidence

Background: The growing consumption of kombucha beverages in the last decade has motivated an increase in the number of scientific studies investigating their biological activities. Their specific microbiological and chemical composition led to the generation of interesting bioactive fractions. Scope and approach: Although many in vitro analyses have been described regarding bioactivities of kombucha and kombucha ingredients, a significantly lower amount of in vivo tests have been published and, moreover, clinical trials are particularly missing. In this revision, several biological activities were reviewed through the scientific literature (antioxidant, immune-modulatory, antiproliferative, hypocholesterolemic, antihypertensive, hypoglycemic, antimicrobial), describing the utilized experimental model, the reported results and their potential implications on human health. Furthermore, strengths and weaknesses of the current evidences around kombucha bioactivities were pointed out. Key findings and conclusions: It can be concluded that, despite of the interesting results obtained in vitro, further research is required including more in vivo tests, bioaccessibility and bioavailability assessment and clinical trials, as well as the isolation of bioactive compounds allowing the study of single molecules and their functionality.