TEA ENHANCES INSULIN ACTIVITY

Authors: Anderson, Richard; Polansky, Marilyn

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2002
Publication Date: 11/1/2002
Citation: Anderson, R.A., Polansky, M.M. 2002. Tea enhances insulin activity. Journal of Agricultural and Food Chemistry. 50:7182-7186, 2002

Interpretive Summary: The lack of control of blood sugar leading to glucose intolerance and ultimately diabetes is one of the leading causes of poor health. The incidence of diabetes is expected to double in the next two to three decades. This study determined the potential improvements in the control of blood sugar by the consumption of tea and determined the active ingredients in tea. Tea, as normally consumed, was shown to increase insulin activity more than 20-fold in a laboratory assay. Black, green and oolong teas, but not herbal teas, which are not teas in the traditional sense since they do not contain leaves of Camellia senensis, were all shown to increase insulin activity. Separation of the components of green tea extracts showed that essentially all of the insulin potentiating activity was in the fraction containing epigallocatechin gallate, a component that has also been shown to be an antioxidant. Similar results were found with black tea but there was also some activity in the region of the theaflavins. These data demonstrate that tea contains in vitro insulin enhancing activity and the predominant active ingredient is epigallocatechin gallate. Further studies are required to determine if tea has beneficial effects on people with glucose intolerance or diabetes. This work is of potential benefit to the millions of people worldwide who have elevated levels of blood sugar.

Technical Abstract: 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 more than 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 since 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 activity. Addition of lemon to the tea did not affect insulin potentiating activity. Addition of 5 grams of 2% milk per cup decreased insulin potentiating activity one third and 50 grams of milk per cup decreased insulin potentiating activity approximately 90%. Nondairy creamers, and soy milk also decreased insulin enhancing activity. These data demonstrate that tea contains in vitro insulin enhancing activity and the predominant active ingredient is epigallocatechin gallate.