About 60 years ago, Dr. Minowada of Kyoto University noticed that sugar in the urine of patients hospitalized for diabetes fell markedly during periods when they participated in chanoyu (Tea Ceremony). He reported that powdered tea of the type used in the traditional Tea Ceremony had the capability of lowering blood sugar. Unfortunately, however, this important report was ignored due to the outbreak of World War II and the subsequent postwar food shortages. But the arrival of the gourmet era in recent years in Japan has led to heightened interest in diabetes and the ability of green tea to reduce blood sugar.
The sugars and carbohydrate in our food are digested mainly in the duodenum, converted there to glucose and then absorbed into the blood. The agent that regulates the intake of blood sugar into the tissues is insulin, a chemical secreted from Langerhans islets on the pancreas. Diabetes is a disease characterized by insufficient secretion or improper functioning of insulin, which hinders the proper absorption of glucose into the tissues and leads to a high concentration of blood sugar that must eventually be excreted into the urine. If this high concentration of blood sugar should continue for a long period, it will affect the vascular system and cause a number of quite serious diseases including atherosclerosis and retinal hemorrhages. Dr. Hara(#10) gave dried green tea catechin in edible form to mice that were subject to hereditary diabetes and verified a lowering of their blood sugar. In parallel experiments, Dr. Shimizu(#11) gave an extract of green tea to mice and demonstrated that it had the ability to lower blood sugar. It has also been shown that the polysaccharides in green tea possess the same ability. Although these results come from animal tests, the evidence that green tea catechin and polysaccharides can lower blood sugar In mice may also, in light of Dr. Minowada's old report, apply to humans.

(#10) H. Asai, Y. Kuno, H. Ogawa, Y. Hara and K. Nakamura, Kiso to Rinsshyo, 21, 163 (1987).
(#11) M. Shimizu et al., Yakugaku Zasshi, 108, 964 (1988).