Journal of Tea Science Research, 2024, Vol.14, No.2, 102-111 http://hortherbpublisher.com/index.php/jtsr 104 3 Epidemiological Evidence 3.1 Population studies on tea consumption and disease prevention Numerous population studies have investigated the relationship between tea consumption and the prevention of chronic diseases. For instance, long-term consumption of diets rich in polyphenols, including tea, has been associated with a reduced risk of developing various chronic diseases such as cardiovascular diseases (CVDs), cancer, diabetes, and neurodegenerative diseases (Rudrapal et al., 2022a; 2022b). Specifically, green tea has been highlighted for its chemopreventive effects against lung cancer induced by cigarette smoke (Rudrapal et al., 2022b). Additionally, tea polyphenols have been shown to regulate gut flora, which plays a crucial role in maintaining overall health and preventing chronic diseases (Wang et al., 2022). 3.2 Statistical correlations between tea polyphenols and chronic diseases Statistical analyses from various studies have demonstrated significant correlations between tea polyphenol intake and reduced incidence of chronic diseases. For example, polyphenols from green tea have been shown to reduce the oxidation of low-density lipoprotein cholesterol (LDL-C), which is a key factor in the development of atherosclerosis and cardiovascular diseases (Cicero and Colletti, 2018; Tung et al., 2020). The antioxidant properties of tea polyphenols have been linked to their ability to protect against oxidative stress-related disorders, including cancer and neurodegenerative diseases (Figure 2) (Zhao et al., 2019; Yan et al., 2020; Rudrapal et al., 2022a). Studies have also shown that regular consumption of tea can lead to significant improvements in antioxidant capacity, which is crucial for preventing oxidative damage and associated chronic conditions (Baeza et al., 2018; Zhang et al., 2018). Figure 2 The cellular pathways regulated by tea polyphenols during their antioxidant activity (Adopted from Yan et al., 2020) Image caption: AKT = protein kinase B; AMPK = adenosine 5'-monophosphate; Pi3-K = Pi3 kinase; ROS = reactive oxygen species; keap1 = Kelch-like ECH-associated protein-1; Nrf2 = nuclear factor erythroid 2-related factor 2; ERK = extracellular-signal-regulated kinase; JNK = c-Jun N-terminal kinase; NF-κB = nuclear factor-kappa B; I-κB = inhibitory protein inhibitor of NF-κB; SOD = superoxide dismutase; CAT = catalase; HO-1 = heme oxygenase-1; NQO1 = quinone oxidoreductase 1; GSH = glutathione; ARE = antioxidant response element; p-ERK = phosphorylated ERK; AP-1 = activating protein-1 (Adopted from Yan et al., 2020) Yan et al. (2020) illustrates the significant impact of tea polyphenols on reducing oxidative stress and inflammation through the regulation of key cellular signaling pathways. By modulating pathways such as Pi3-K/AKT, AMPK, ERK, JNK, and NF-κB, tea polyphenols enhance antioxidant enzyme activity and reduce reactive oxygen species (ROS) levels. This regulatory action helps protect cells from oxidative damage and inflammation, contributing to the prevention of diseases like cancer, cardiovascular issues, and obesity. The
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