Beneficial Effects of Green Tea Catechins on Neurological Disorders

Abstract

Green tea is natural dried leaves of the tea plant, Camellia sinensis. This “nonfermented” tea contains more catechins than black tea (oxidized green tea) or oolong tea (partially oxidized tea). The composition of tea leaves depends on a variety of factors, including climate, season, horticultural practices, and the type and age of the plant. Green and black teas contain polyphenols, alkaloids (caffeine, theophylline, and theobromine), flavonols (quercetin, kaempferol, and rutin), amino acids, carbohydrates, proteins, chlorophyll, volatile organic compounds that contribute to tea flavonoid, fluoride, aluminum, minerals, and trace elements (Fig. 5.1). Green tea contains gallic acid (GA), chlorogenic acid, and caffeic acid, and flavonols such as kaempferol, myricetin, and quercetin (USDA data base 2003; Wang and Ho 2009). In contrast, black tea mostly has the polymerized catechins such as theaflavins and thearubigins. Collectively, these studies indicate that green tea is the source of catechins—simple flavonoids whereas black tea is rich in theaflavins and thearubigins, which are generated during the process of oxidation (USDA data base 2003; Wang and Ho 2009). Four major theaflavins have been identified from black tea, including theaflavin, theaflavin-3-gallate, theaflavin-3′-gallate, and theaflavin-3,3′-digallate. Catechins are strong antioxidants that can quench reactive oxygen species (ROS) such as super oxide radical, singlet oxygen, hydroxyl radical, peroxyl radical, nitric oxide, nitrogen dioxide, and peroxynitrite (Feng 2006). Since ancient times, green tea has been considered by the traditional Chinese and Japanese medicine as a healthful beverage. Human studies indicate that green tea not only contributes to a reduction in the risk of cardiovascular disease and some forms of cancer, but also induces antihypertensive effects by suppressing angiotensin I-converting enzyme, body weight control by suppressing the appetite, antibacterial, and antivirasic effects, solar ultraviolet protection, bone mineral density increase, antifibrotic effects, and neuroprotective effects. Green tea also decreases blood pressure (Henry and Stephens-Larson 1984) and blood sugar (Matsumoto et al. 1993). Lipid metabolism studies in animals, tissues, and cells have found that tea extract and catechins reduce triacylglycerol and total cholesterol concentrations (Nanjo et al. 1994; Chan et al. 1999), inhibit hepatic and body fat accumulation (Ishigaki et al. 1991), and stimulate thermogenesis (Dulloo et al. 2000). In addition, green tea boosts metabolism and improves immune function.