The Role of Polyphenols on Cognitive Function and Dementia Through Gut-Microbiota-Brain Axis Modulation: A Narrative Review.

The number of individuals affected by dementia and cognitive decline is progressively increasing, becoming a serious global health challenge. Several investigations underline the role of nutrition and dietary habits as a preventive strategy. Recent studies suggest that dietary supplementation with polyphenols may constitute an efficient preventive strategy. Indeed, it is emerging that polyphenols exhibit a neuroprotective effect because of their pronounced antioxidant and anti-inflammatory activity. Notably, several studies underline the role of the gut microbiota in the metabolism of the polyphenols, producing bioactive molecules that are absorbed through the gastrointestinal tract. They may exhibit beneficial effects on the central nervous system. Moreover, dietary polyphenols modulate gut microbiota composition, demonstrating a reciprocal regulation between gut microbiota and polyphenol-induced effects on brain functions. Thus, polyphenols are proposed to have an important role on the gut-microbiota-brain axis regulation. The literature search for this narrative review was conducted across three electronic databases PubMed, Scopus, and Web of Science as well as the NIH ClinicalTrials.gov registry, covering the period from January 2000 to 10 February 2026. The following search terms were used: "polyphenols", "microbiota", "gut-brain axis", "dementia", "cognitive function", "polyphenols and cognitive dysfunction", and "polyphenols and microbiota". The study selection process was performed in two sequential stages: (i) screening of titles and abstracts, followed by (ii) full-text assessment for eligibility. Articles were included if they were peer-reviewed studies (in vitro, in vivo, or clinical trials), published in English, and addressed the effects of polyphenols on cognitive outcomes, gut microbiota composition, or the gut-microbiota-brain axis. Exclusion criteria included non-peer-reviewed sources, studies lacking relevant cognitive or microbiota-related endpoints, and publications not available in full.