Tea comes in four common varieties: black, green, white and oolong. Green tea, made from unfermented leaves, has the highest concentration of polyphenols, a type of antioxidant. Antioxidants help prevent cell damage by removing free radicals caused by toxins and other substances. The most beneficial polyphenol in green tea appears to be epigallocatechin gallate, also called EGCG.
Heart-Related Benefits
Green tea slightly lowers total cholesterol and raises high-density lipoprotein, or HDL -- the "good" cholesterol -- while lowering low-density lipoprotein, or LDL, known as the "bad" cholesterol, according to most but not all studies. The United States Food and Drug Administration, however, denied a petition to allow tea makers to claim on their labels that tea reduces the risk of heart disease, stating the claim lacked sufficient credible evidence.
Cancer Benefits
Studies have examined treatment or prevention benefits from green tea in colon, breast, ovary, prostate and lung cancers, but results have been mixed. In a promising study conducted by the University of Parma in Italy and reported by lead author S. Bettuzzi in the Jan. 15, 2006 "Cancer Research," 60 men with premalignant prostate cells were followed for one year. Half received green tea catechins -- polyphenols extracted from the tea leaves -- while the other half took placebos. Normally, 30 percent of people with this condition would be expected to develop prostate cancer within one year. After one year, 30 percent of the placebo group developed prostate cancer, while only one of the 30, or 3 percent, of the subjects in the green tea group developed cancer.
Weight Loss Benefits
Green tea may aid in weight loss by increasing metabolism, according to a 1999 study reported in the "American Journal of Clinical Nutrition." The study, reported by lead author Abdul Dulloo and conducted jointly by the University of Geneva; Geneva University Hospital; and Laboratoires Arkopharma in Nice, France, found that people taking green tea extract containing 50 mg of caffeine and 90 mg of EGCG three times a day had significant increases in energy expenditure compared with those taking just caffeine or placebo.
References
- University of Maryland Medical Center: Green Tea
- PubMed:Chemoprevention of Human Prostate Cancer by Oral Administration of Green Tea Catechins in Volunteer With High-grade Prostate Intraepithelial Neoplasia: a Preliminary Report From a One-year Proof-of-Principle Study; S. Bettuzzi et al; 2006
- University of Michigan Medical Center: Green Tea
- National Cancer Institute: Tea and Cancer Prevention: Strengths and Limits of the Evidence
- "American Journal of Clinical Nutrition:" Efficacy of a Green Tea Extract Rich in Catechin Polyphenols and Caffeine in Increasing 24-h Energy Expenditure and Fat Oxidation in Humans; Abdul Dulloo; December 1999
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