A comprehensive review on bioavailability, safety and antidepressant potential of natural bioactive components from tea.

Depression is a global public health issue with high morbidity and mortality, which tends to cause fatigue, inability to concentrate, insomnia, and loss of appetite, especially represented by major depressive disorder (MDD). Pathologically, depression is associated with hyperactivity of hypothalamic-pituitaryadrenal (HPA) axis, inflammation, loss of monoaminergic system, and disturbance of gut microbiota. Epidemiological studies have shown that regular tea drinking can reduce the risk of depression. Tea bioactive compounds (L-theanine, catechin, tea pigment and GABA) can regulate depression by inhibiting hyperactive HPA axis, reducing the inflammatory response, restoring the monoaminergic system, inhibiting monoamine oxidase levels, increasing the enrichment of intestinal flora and promoting microbial-gut-brain axis activity. This review discusses the composition, structure, bioavailability and safety of bioactive components from tea, and focuses on exploring the possible pathways of tea bioactive compounds in the regulation of depression. In addition, the low bioavailability of natural bioactive compounds from tea limits the efficacy on depression. Emerging technologies (such as metabolomics, proteomics, and genomics) and nano-encapsulation can be utilized to improve the stability and bioavailability of tea active ingredients, and reduce the potential biotoxicity. The review provides a theoretical basis of utilization of tea active compounds for formulating the prevention and treatment of depression.