Anderson Richard A, Polansky Marilyn M
Nutrient Requirements and Functions Laboratory, Beltsville Human Nutrition Research Center, U.S. Department of Agriculture, Beltsville, Maryland 20705, USA.
J Agric Food Chem. 2002 Nov 20;50(24):7182-6. doi: 10.1021/jf020514c.
The most widely known health benefits of tea relate to the polyphenols as the principal active ingredients in protection against oxidative damage and in antibacterial, antiviral, anticarcinogenic, and antimutagenic activities, but polyphenols in tea may also increase insulin activity. The objective of this study was to determine the insulin-enhancing properties of tea and its components. Tea, as normally consumed, was shown to increase insulin activity >15-fold in vitro in an epididymal fat cell assay. Black, green, and oolong teas but not herbal teas, which are not teas in the traditional sense because they do not contain leaves of Camellia senensis, were all shown to increase insulin activity. High-performance liquid chromatography fractionation of tea extracts utilizing a Waters SymmetryPrep C18 column showed that the majority of the insulin-potentiating activity for green and oolong teas was due to epigallocatechin gallate. For black tea, the activity was present in several regions of the chromatogram corresponding to, in addition to epigallocatechin gallate, tannins, theaflavins, and other undefined compounds. Several known compounds found in tea were shown to enhance insulin with the greatest activity due to epigallocatechin gallate followed by epicatechin gallate, tannins, and theaflavins. Caffeine, catechin, and epicatechin displayed insignificant insulin-enhancing activities. Addition of lemon to the tea did not affect the insulin-potentiating activity. Addition of 5 g of 2% milk per cup decreased the insulin-potentiating activity one-third, and addition of 50 g of milk per cup decreased the insulin-potentiating activity approximately 90%. Nondairy creamers and soy milk also decreased the insulin-enhancing activity. These data demonstrate that tea contains in vitro insulin-enhancing activity and the predominant active ingredient is epigallocatechin gallate.
茶最为人所知的健康益处与多酚类物质有关，多酚是其主要活性成分，具有抗氧化损伤、抗菌、抗病毒、抗癌和抗诱变活性，但茶中的多酚类物质也可能增强胰岛素活性。本研究的目的是确定茶及其成分增强胰岛素的特性。在附睾脂肪细胞试验中，正常饮用的茶在体外可使胰岛素活性提高15倍以上。红茶、绿茶和乌龙茶均能增强胰岛素活性，而传统意义上不属于茶的花草茶（因为它们不含茶树的叶子）则不能。利用沃特世SymmetryPrep C18柱对茶提取物进行高效液相色谱分离显示，绿茶和乌龙茶增强胰岛素活性的主要成分是表没食子儿茶素没食子酸酯。对于红茶，除表没食子儿茶素没食子酸酯外，色谱图的几个区域都有活性，这些区域还对应单宁、茶黄素和其他未定义的化合物。茶中发现的几种已知化合物都能增强胰岛素活性，其中表没食子儿茶素没食子酸酯活性最强，其次是表儿茶素没食子酸酯、单宁和茶黄素。咖啡因、儿茶素和表儿茶素的胰岛素增强活性不显著。往茶中加柠檬不影响其增强胰岛素的活性。每杯加5克2%的牛奶会使增强胰岛素的活性降低三分之一，每杯加50克牛奶会使增强胰岛素的活性降低约90%。非乳制奶精和豆浆也会降低增强胰岛素的活性。这些数据表明，茶具有体外增强胰岛素的活性，其主要活性成分是表没食子儿茶素没食子酸酯。
