Green Tea

Green tea is commonly consumed as an infusion made by steeping dried or powdered leaves in hot water. Traditional forms include loose leaf tea and powdered green tea known as matcha, especially in Japan. It can be consumed plain or with additions such as lemon or honey. Green tea extracts are also available in liquid or supplement forms. The preparation methods and serving styles vary by culture but generally aim to preserve the natural antioxidants present in the leaves.

Botanical Origin and Processing

Green tea is produced from the leaves of Camellia sinensis. Unlike black or Oolong tea, green tea undergoes minimal processing. The freshly harvested leaves are steamed immediately to prevent fermentation, preserving natural polyphenols, particularly catechins. This processing method maintains the green color and preserves compounds believed to contribute to health effects.

Chemical Composition

Green tea leaves contain a complex array of compounds including proteins, amino acids (such as theanine), carbohydrates, minerals, trace elements, caffeine, vitamins, and polyphenols. Polyphenols, especially flavanols known as catechins (including epicatechin, epigallocatechin, epicatechin-3-gallate, and (-)-epigallocatechin-3-gallate [EGCG]), make up about 30% of the dry leaf weight and are central to green tea’s biological activities.

Biological Activities and Health Effects

• Antioxidant Properties: Green tea catechins exhibit antioxidant effects by neutralizing reactive oxygen species and modulating antioxidant enzymes such as superoxide dismutase and catalase, thereby protecting cells from oxidative stress.
• Effects on Cancer and Cardiovascular Diseases: Experimental studies suggest that green tea catechins may have antiproliferative and antitumorigenic properties in various cancers and may reduce cardiovascular disease risk by lowering blood pressure and improving lipid profiles.
• Neuroprotective and Immune-Modulating Effects: Green tea components have shown potential neuroprotective effects in models of neurodegenerative diseases and may modulate immune responses.
• Bone Health: Green tea consumption has been associated with increased bone mineral density, suggesting a role in reducing fracture risk.
• Effects on Carbohydrate Metabolism and Diabetes: Green tea catechins have demonstrated hypoglycemic effects in animal models by improving glucose tolerance, reducing blood glucose levels, and enhancing antioxidant defenses. EGCG mimics insulin activity and reduces expression of gluconeogenic enzymes. Some human studies indicate improved glucose metabolism, though further research is required.
• Antiobesity Effects: Green tea catechins may aid weight management through increased energy expenditure, enhanced fat oxidation, and modulation of lipid metabolism. Clinical studies report increased postprandial thermogenesis and fat oxidation, but optimal dosing and mechanisms need clarification.
• Safety and Adverse Effects: High doses of green tea catechins, particularly EGCG, may induce cytotoxicity, including liver toxicity and pro-oxidant effects in pancreatic cells. Potential adverse effects include thyroid enlargement, reduced iron bioavailability, caffeine-related risks, and aluminum accumulation concerns. Individuals with cardiovascular conditions, pregnant or breastfeeding women, and those taking certain medications should exercise caution.

Green Tea in Japanese Culture

Green tea holds a significant cultural and historical role in Japan, where it was first introduced in the 17th century from India. The Japanese tea ceremony (chanoyu or sado) is a ritualized form of preparing and drinking powdered green tea (matcha), embodying principles of harmony, respect, purity, and tranquility. Green tea is consumed daily by many in Japan, reflecting both social and health values. The preservation of green tea’s flavor and nutrients through steaming, a distinct processing method, is a hallmark of Japanese tea production. The integration of green tea into various culinary, medicinal, and social contexts underscores its cultural importance beyond its biochemical properties.