"To our knowledge, we provide the first evidence that EGCG consumed in the diet exerts potent antidiabetic activity in vivo in a dose-dependent manner," wrote lead author Swen Wolfram from DSM Nutritional Products in the Journal of Nutrition (Vol. 136, pp. 2512-2518).
An estimated 19 million people are affected by diabetes in the EU 25, equal to four per cent of the total population. This figure is projected to increase to 26 million by 2030.
In the US, there are over 20 million people with diabetes, equal to seven per cent of the population. The total costs are thought to be as much as $132bn, with $92bn being direct costs from medication, according to 2002 American Diabetes Association figures.
Dietary supplementation with EGCG could contribute to anti-diabetic nutritional strategies if the results of the new study can be translated to humans.
The research, which used DSM's high purity green tea leaf extract Teavigo (greater than 94 per cent EGCG and less than five per cent other catechins), used two rodent models of type 2 diabetes mellitus, as well as investigating the effect of the extract on rat liver (H4IIE) cells.
Thirty-six severely diabetic male mice were divided into four groups and fed a modified AIN-93 diet supplemented with one of three doses of EGCG (2.5, 5.0, or 10.0 grams per kilogram of diet) or placebo for seven weeks. After five weeks the researchers performed an oral glucose tolerance test, and after six weeks an insulin tolerance test. At the end of the test, blood samples were taken to analyse glucose, free fatty acids, triacylcglyceride levels.
Dr. Wolfram and his colleagues report that, after five weeks, glucose tolerance was improved in a dose-dependent manner, with the effect most noticeable in food-deprived mice. EGCG dietary supplementation lead to reductions in glucose levels of 23, 35, and 48 per cent for the 2.5, 5.0, or 10.0 g/kg diets, respectively.
Plasma triacylglyceride concentrations were reduced by 0.25, 0.5, and 1.0 per cent for the 2.5, 5.0, or 10.0 g/kg diets, respectively, and plasma insulin levels were increased in a dose-dependent manner, said the researchers.
Dietary supplementation of mildly diabetic rats with EGCG (5 g/kg of diet) for ten weeks resulted in improved oral glucose tolerance, blood glucoses levels, lower free fatty acid plasma concentrations, as well as increasing plasma insulin concentrations 15 minutes after EGCG supplementation.
Separate experiments with rat liver (H4IIE) cells allowed the researchers to investigate the potential mechanism behind the apparent benefits, and Wolfram reported that EGCG downregulated genes involved in gluconeogenesis, as well as genes involved in the synthesis of fatty acids, triacylgycerol, and cholesterol.
"Our data suggest that supplementation with EGCG could potentially improve glucose tolerance in humans with type-2 diabetes mellitus," concluded the researchers. "This hypothesis should now be investigated in randomised placebo-controlled trials."
Indeed, Dr. Wolfram confirmed to NutraIngredients.com that DSM Nutritional Products were planning to start such a trial in the near future.
Consumer awareness of the benefits of green tea and green tea extracts continues to rise with growing numbers of studies, from 430 papers in 2000 to almost 1500 in 2003, reporting benefits of the main compounds, catechins.
This has seen European demand surge, having reached 500 metric tonnes in 2003. Companies such as DSM's Teavigo, and Taiyo International's Sunphenon (more than 90 per cent purity), position themselves firmly in specific catechin markets.