Health Functions and Related Molecular Mechanisms of Tea Components: An Update Review

Abstract

Tea is widely consumed all over the world. Generally, tea is divided into six categories: White, green, yellow, oolong, black, and dark teas, based on the fermentation degree. Tea contains abundant phytochemicals, such as polyphenols, pigments, polysaccharides, alkaloids, free amino acids, and saponins. However, the bioavailability of tea phytochemicals is relatively low. Thus, some novel technologies like nanotechnology have been developed to improve the bioavailability of tea bioactive components and consequently enhance the bioactivity. So far, many studies have demonstrated that tea shows various health functions, such as antioxidant, anti-inflammatory, immuno-regulatory, anticancer, cardiovascular-protective, anti-diabetic, anti-obesity, and hepato-protective effects. Moreover, it is also considered that drinking tea is safe to humans, since reports about the severe adverse effects of tea consumption are rare. In order to provide a better understanding of tea and its health potential, this review summarizes and discusses recent literature on the bioactive components, bioavailability, health functions, and safety issues of tea, with special attention paid to the related molecular mechanisms of tea health functions.

Keywords: Camellia sinensis; bioavailability; catechins; health benefits; phytochemicals; safety; tea.

Figure 1

The main health functions of tea.

Figure 2

Chemical structures of several bioactive compounds in tea.

Figure 3

The molecular mechanisms of tea antioxidants (TAs) with contrasting influences on cancer and normal cells. In cancer cells, TAs inhibit the expression and activity of sirtuin 3 (SIRT3), leading to mitochondrial reactive oxygen species (ROS) accumulation, mitochondrial dysfunction, and ultimately cell death. In normal cells, TAs activates SIRT3 and related downstream antioxidant responsive genes (AOX genes, including superoxide dismutase 2 (SOD2) and glutathione peroxidase 1 (GPX1)), preventing cells from oxidative damage. Abbreviations: ERRα, estrogen-related receptor α; PGC-1α, peroxisome proliferator-activated receptor γ coactivator 1α.

Figure 4

Main molecular targets of tea on targeting cancer. Abbreviations: Akt, protein kinase B; Bax, Bcl-2-associated X protein; Bcl-2, B-cell lymphoma 2; CAT, catalase; CDK, cyclin-dependent kinase; GPX, glutathione peroxidase; IL, interleukin; MAPK, mitogen-activated protein kinase; MCL-1, myeloid cell leukemia 1; MMP, matrix metallopeptidase; NF-κB, nuclear factor κB; NK, natural killer; SIRT, sirtuin; SOD, superoxide dismutase.