~ 081508 Green Tea Extract Improves Glucose Control In Borderline Diabetics

The August, 2008 issue of the European Journal of Clinical Nutrition published the discovery of researchers in Japan that supplementing the diet with green tea extract improves fasting hemoglobin A1c, a blood marker that is regularly tested in diabetics to assess long term glucose control. While fasting glucose provides an immediate measurement of blood glucose levels, hemoglobin A1c assesses glycation, a process that occurs when blood sugar molecules bind with proteins such as hemoglobin. The excessive glycation that occurs in people with consistently elevated blood sugar results in damaged tissues, which contributes to the apparent accelerated aging observed in diabetic patients. High hemoglobin A1c levels indicate elevated average glucose levels over the three month period prior to testing.

For the current crossover study, researchers at the University of Shizuoka, Osaka University, and Hamamatsu University School of Medicine in Japan enrolled 49 men and 11 women with prediabetes. An early intervention group consisting of 29 participants received a daily green tea extract powder containing 544 milligrams polyphenols (providing 456 milligrams catechins) for two months, followed by two months during which no supplement was received. The participants in the later intervention group received no supplement for the first two months, followed by two months of daily green tea supplementation. Fasting hemoglobin A1c levels were measured at the beginning of the study and at two and four months.

For both groups, fasting hemoglobin A1c levels were found to be significantly reduced from baseline levels following green tea supplementation. Hemoglobin A1c levels declined from 6.2 to 5.9 percent in the early intervention group, and from 6.1 to 5.9 percent in the later intervention group. (Hemoglobin A1c levels in healthy individuals range from 4 to 5.9 percent.) For those in the early intervention group, this reduction remained following the final two months of the study during which no green tea supplement was received. A decrease in diastolic blood pressure was also associated with green tea supplementation, however, its significance was considered borderline.

In their discussion of the findings, the authors cite previous research in which catechins were found to suppress glucose absorption in the small intestine. Insulin-like activities have been attributed to green tea, as well as inhibition of gluconeogenic enzymes. In their introduction to the report, they observe that green tea polyphenols have been associated with anticancer effects, antioxidative activity, antibacterial effects and antioxidative activity against low-density lipoprotein cholesterol, as well as a reduction in cholesterol, body weight and fat, and blood glucose. The current findings contribute to the growing body of knowledge concerning the benefits associated with green tea, and may be of particular interest to diabetic patients or those at risk of the disease.


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