Lee Swanson Research Update

Green Tea Review Suggests Many Health Benefits

November 2010

Researchers at the NPO International Laboratory of Biochemistry in Japan recently undertook a review of scientific literature showing the benefits of green tea in promoting health. The review was published in the journal Chinese Medicine.

Researchers said: “The health benefits of green tea for a wide variety of ailments, including heart disease and liver disease, were reported. Many of these beneficial effects of green tea are related to its catechin, particularly (-)-epigallocatechin-3-gallate, content. There is evidence from in vitro and animal studies of the underlying mechanisms of green tea catechins and their biological actions. There are also human studies on using green tea catechins to treat metabolic syndrome, such as obesity, type 2 diabetes and cardiovascular risk factors.”

For their review, the authors searched PubMed, EMBASE, AMED and China Academic Journals Full Text Database. They included articles about green tea’s health benefits in humans and animals, absorption of metal ions, antioxidation and inhibition of oxidative stress, carbohydrate metabolism, diabetes mellitus and more. The authors selected 105 peer-reviewed articles in English for the review.

Cited in the review are animal studies reporting that green tea catechins provide some protection against degenerative diseases.

Several epidemiological studies and clinical trials have shown that green tea may reduce the risk of chronic diseases, particularly hypertension and coronary heart disease. Other cited animal and human studies report an inhibitory effect of green tea on Helicobacter pylori infection and on the influenza virus, as well as an antifungal activity against Candida albicans.

Green tea consumption has also been associated with increased bone mineral density and protection against hip fractures. The authors report that tea catechins can affect iron absorption, particularly in those at risk for iron deficiency.

Green tea catechins, along with the antioxidant vitamins C and E and certain enzymes (superoxide dismutase and catalase) are hypothesized to contribute to the total antioxidant defense system.

In vivo studies have reported that green tea catechins increase total plasma antioxidant activity. The content of the oxidative stress marker malondialdehyde has been shown to decrease after green tea intake. One cited study of 25 patients with different gastrointestinal complaints measured the tolerance of green tea tablets and their effect on antioxidant status indices; a decreased level of oxidative stress was seen in the treatment group.

Tea catechins, especially EGCG, appear to have anti-obesity and anti-diabetic effects. Recent data from human studies indicate that the consumption of green tea or green tea extracts may help reduce body weight, mainly body fat, by increasing postprandial thermogenesis and fat oxidation.

Cited studies in animal models of diabetes reported reductions in serum glucose levels with the administration of green tea polyphenols. In normal rats, green tea catechins reduced plasma triglyceride levels in an oral glucose-tolerance test. Green tea and green tea extracts have been demonstrated to modify glucose metabolism beneficially in experimental models of type 2 diabetes mellitus. A human study reported that green tea promoted glucose metabolism in healthy human volunteers as shown in oral glucose-tolerance tests.

The authors conclude that long-term consumption of tea catechins could be beneficial to high-fat diet-induced obesity and type 2 diabetes and could reduce the risk for coronary disease. They also added that further research should focus on the pharmacological and clinical effects of green tea and its mechanisms of action.

Chinese Medicine 5:13-21, 2010

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