Anticancer Effects and Molecular Target of Theaflavins from Black Tea Fermentation <i>in Vitro</i> and <i>in Vivo</i>

Black tea is one of the most popular beverages in the world, and numerous epidemiological studies have shown that drinking black tea is good for health. As a natural tea pigment formed during the fermentation of black tea, the content of theaflavins accounts for only 2–6% of the dry weight of black tea, but they have a great impact on the color and taste of black tea soup. Recently, a large number of studies have shown that theaflavins have a significant anticancer effect. In this Perspective, we first state the physical and chemical properties, separation and purification methods, and biological formation pathways of theaflavins and analyze their safety and oral bioavailability and the structure–activity relationship of their antioxidant and anticancer activities; then, we describe in detail their anticancer effect in vitro and in vivo and highlight their various molecular targets involved in cancer inhibition. The anticancer molecular targets of theaflavins are mainly cell-cycle regulatory proteins, apoptosis-related proteins, cell-migration-related proteins, and growth transcription factors. Finally, the possibility of developing new health-care food based on theaflavins is discussed. This Perspective is expected to provide a theoretical basis for the anticancer application of theaflavins in the future.