Overview and Health Benefits

The subtle aroma of freshly brewed Camellia sinensis has long been a hallmark of cultural traditions and medicinal practices, enjoyed in the form of green tea or black tea. Revered for its potent polyphenol content, particularly catechins such as epigallocatechin gallate (EGCG), green tea in particular has gained recognition in herbal medicine for its wide-ranging health benefits. Black and oolong tea require partial fermentation of the leaves, but green tea is produced by steaming fresh leaves, which inactivates oxidising enzymes in the leaves and preserves polyphenol content. From enhancing cardiovascular health to offering protective effects against various forms of cancer, green tea is much more than just a comforting beverage—it's a potent ally in promoting health and longevity. The antioxidant properties of green tea’s bioactive compounds are central to its therapeutic effects, making it a valuable component in the prevention and management of chronic diseases.

Key Benefits

• Antioxidant Powerhouse: Green tea is renowned for its high catechin content, especially EGCG, which significantly contributes to its powerful antioxidant activity. These compounds help neutralise free radicals, thereby reducing oxidative stress—a major contributor to chronic diseases and ageing. This antioxidant action is crucial for maintaining cellular health and preventing damage that could otherwise lead to conditions like cardiovascular disease and neurodegeneration (Lambert & Elias, 2010; Hajam et al., 2022; Vinson et al., 1995).
• Cardiovascular Health: Regular consumption of green tea has been linked to improved cardiovascular outcomes. The catechins in green tea help lower blood pressure, improve lipid profiles, and prevent the oxidation of LDL cholesterol, a key factor in the development of atherosclerosis. Studies suggest that drinking green tea may reduce the risk of heart disease and stroke, highlighting its role as a cardioprotective agent (Sano et al., 2004; Sánchez et al., 2020; Vinson et al., 1998). Furthermore, green tea polyphenols promote hepatic detoxification pathways and protect against cardiac toxicity during chemotherapy (Sengottuvelu et al., 2008).
• Cancer Prevention: The potential anticancer effects of green tea are widely studied, with evidence suggesting that EGCG may inhibit cancer cell growth and metastasis (Yang et al., 2011). Green tea catechins interfere with cellular mechanisms of various cancers, including breast, prostate, and colorectal cancers, by promoting apoptosis and inhibiting angiogenesis, thereby reducing tumour growth and spread (Pastore & Fratellone, 2006; Demeule et al., 2002). Additionally, green tea has been shown to inhibit key pathways involved in tumour initiation, growth, and metastasis, such as NF-kappa B and VEGF, and to potentiate the effects of certain chemotherapeutic agents while protecting against their side effects (Lambert & Elias, 2010).
• Metabolic and Endocrine Regulation: Green tea supports metabolic health by enhancing insulin sensitivity and glucose metabolism. These effects are particularly beneficial for individuals with or at risk of type 2 diabetes, as they help regulate blood sugar levels and reduce the risk of diabetes-related complications (Sánchez et al., 2020). Additionally, green tea’s thermogenic properties aid in weight management by increasing fat oxidation and improving lipid metabolism, making it a popular component of weight loss regimens (Hursel et al., 2011; Hodgson et al., 2013; Sánchez et al., 2020).
• Neuroprotective Effects: The neuroprotective properties of green tea, attributed largely to EGCG, include the potential to protect against neurodegenerative diseases like Alzheimer’s and Parkinson’s (Mandel & Youdim, 2004). Green tea polyphenols help reduce inflammation and oxidative stress in the brain, which are key contributors to neurodegeneration. Moreover, green tea has been shown to enhance cognitive function, possibly due to its effects on neurotransmitter regulation and the protection of neuronal cells from oxidative damage (Scholey et al., 2012).
• Antimicrobial and Antiviral Properties: Green tea has demonstrated significant antibacterial and antiviral effects (Steinmann et al., 2012). The catechins in green tea, particularly EGCG, are effective against a range of pathogens, including Staphylococcus aureus, Helicobacter pylori, and various viruses such as HIV, HPV, and influenza (Sugita-Konishi et al., 1999; Carneiro et al., 2016). These properties make green tea a valuable natural remedy for preventing and managing infections.

Safety

While green tea is celebrated for its numerous health benefits, it is important to approach its consumption with awareness of potential cautions and contraindications. Green tea contains tannins, which can inhibit iron absorption, making it advisable to leave at least two hours between consuming tea and iron-rich foods or supplements (Disler et al., 1975). The caffeine present in green tea, though moderate, acts as a stimulant and diuretic, which can be problematic for individuals sensitive to caffeine or those with anxiety disorders, insomnia, or certain cardiovascular conditions (Hodgson et al., 2013). Excessive intake of green tea, particularly in supplement form, can lead to adverse effects such as gastrointestinal discomfort, liver toxicity, and impaired iron absorption due to its high tannin content (Bonkovsky, 2006). Moreover, the caffeine present in green tea, although relatively moderate, can exacerbate conditions like anxiety disorders, insomnia, and certain heart conditions, and may interact with medications such as blood thinners, beta-blockers, and stimulants (Hodgson et al., 2013). Additionally, studies have shown conflicting evidence regarding the interaction between Camellia sinensis and certain cancer medications, suggesting that those undergoing treatment should seek expert advice (Schönthal, 2011). It's important to note that the risks associated with green tea or its active compound, EGCG, generally arise with very high doses, far above what is typically consumed in a daily diet (Schönthal, 2011). Green tea polyphenols have also been shown to inhibit the activity of certain drug-metabolising enzymes, which could alter the effectiveness of prescription medications, including chemotherapy agents and anticoagulants (Lambert & Yang, 2003). 

Therefore, as with any herbal remedy, it is best to consult with a qualified medical herbalist before using green tea in significant doses for medicinal purposes, especially if you have a pre-existing medical condition or are taking any prescription medications.