Health Effects of Green Tea
Green tea contains polyphenols which are thought to improve health, particularly catechins, the most abundant of which is epigallocatechin gallate. In vitro and animal studies as well as preliminary observational and clinical studies of humans suggest that green tea can reduce the risk of cardiovascular disease and cancer as well as beneficially impact bone density, cognitive function, dental caries, and kidney stones. However, the human studies are sometimes mixed and inconsistent. Green tea also contains carotenoids, tocopherols, ascorbic acid (vitamin C), minerals such as Cr, Mn, Se or Zn, and certain phytochemical compounds. It is a more potent antioxidant than black tea, although black tea has substances which green tea does not such as theaflavin.
Green tea consumption is epidemiologically associated with reduced heart disease, and animal studies have found that it can reduce cholesterol. However, several small, brief human trials found that tea consumption did not reduce in cholesterol in humans. In 2003 a randomized clinical trial found that a green tea extract with added theaflavin from black tea reduced cholesterol.
In a study performed at Birmingham (UK) University, it was shown that average fat oxidation rates were 17% higher after ingestion of green tea Extract than after ingestion of a placebo. Similarly the contribution of fat oxidation to total energy expenditure was also significantly higher by a similar percentage following ingestion of green tea extract. This implies that ingestion of green tea extract can not only increase fat oxidation during moderately intensive exercise but also improve insulin sensitivity and glucose tolerance in healthy young men.
In a study performed at the Technion, it was shown that the main antioxidant polyphenol of green tea extract, EGCG, when fed to mice induced with Parkinson’s and Alzheimer’s disease, helped to protect brain cells from dying, as well as ‘rescuing’ already damaged neurons in the brain, a phenomenon called neurorescue or neurorestoration. The findings of the study, led by Dr. Silvia Mandell, were presented at the Fourth International Scientific Symposium on Tea and Human Health in Washington D.C., in 2007. Resulting tests underway in China, under the auspices of the Michael J. Fox Foundation, are being held on early Parkinson’s patients.
In a recent case-control study of the eating habits of 2,018 women, consumption of mushrooms and green tea was linked to a 90% lower occurrence of breast cancer.
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