Mechanism of tea polyphenols improving sleep by regulating neurotransmitters through the gut microbiota-brain axis

In today's fast-paced modern lifestyle, sleep disorders have become a pervasive challenge for many individuals. Conventional treatments often rely on pharmacological interventions, which carry risks of dependency and adverse effects. In recent years, the gut microbiota has gained increasing recognition as a "second brain," engaging in bidirectional communication with the central nervous system via the microbiota-gut-brain axis (MGB axis). Tea polyphenols (TP), the primary bioactive compounds derived from tea, show considerable potential in improving sleep quality through this microbial-gut-brain circuitry. This review systematically elucidates how TP reshape the gut microbiota by selectively enriching beneficial bacteria such as Lactobacillus and Bifidobacterium, while suppressing pathogenic species. These structural changes are accompanied by functional benefits, including enhanced intestinal barrier integrity and attenuated systemic inflammation. Furthermore, gut microbiota metabolize TP into bioactive small molecules that enter systemic circulation, cross the blood-brain barrier (BBB), and modulate central neurotransmitters, notably serotonin (5-HT) and γ-aminobutyric acid (GABA). By delineating this gut-mediated neuromodulatory network, our study provides a novel theoretical foundation for the use of TP as a dietary strategy to ameliorate sleep disorders.