Teas come in different types, although all teas originate with the leaves of the Camellia sinensis plant. The difference in black, green and oolong teas has to do with the treatment of the leaves. Black tea -- the most common tea consumed in the United States -- is made from fully fermented, oxidized leaves that are wilted and crushed. Green tea is made from unfermented leaves, while oolong tea comes from partially fermented leaves. Of the three, green tea contains the most tannins, a type of polyphenol, or plant chemical with certain health benefits.
Definition
Catechins make up the bulk of tannins in green tea, with epigallocatechin-3-gallate, often abbreviated to EGCG, the most potent and abundant of the catechins. Tannins and other polyphenols have antioxidant properties, meaning that they scavenge and destroy potentially harmful substances called free radicals, which are molecules created by toxins as well as by natural body processes. Antioxidants can damage cell DNA and may lead to diseases such as cancer, diabetes and heart disease.
Potential Cancer Benefits
In numerous laboratory studies, the polyphenols and catechins in tea have induced cell death in cancer cells and inhibited cancer cell's ability to reproduce, the National Cancer Institute reports. One drawback noted by researchers from Rutgers University in the October 2003 issue of "The Journal of Nutrition" is that most studies required concentrations of 10 or 20 micromol/L to achieve an effect. In humans, the peak plasma concentration of EGCG achieved after breakdown after ingestion is 1 micromol/L. More human studies will help determine the benefits of tannins in reducing cancer risks or treating cancer.
Potential Heart Benefits
Tannins in green tea may contribute to lower cholesterol levels and a decreased risk of developing atherosclerosis, a buildup of plaque on the interior walls of blood vessels that can increase the risk of heart attack and stroke. A Vanderbilt University project reported in the June 2003 issue of "Archives of Internal Medicine" studied the effect of a 375 mg green tea extract capsule compared to a placebo on Chinese subjects with mild to moderately elevated cholesterol over a 12-week period. Total cholesterol dropped 11.3 percent and low-density lipoprotein, the "bad" form of cholesterol, decreased by 16 percent in subjects taking the green tea extract, while no changes were noted in the placebo group.
Potential Weight-Loss Benefits
Catechins in green tea have been touted as a possible weight-loss aid by increasing metabolism, which burns more calories and also by decreasing fat stores. A Japanese study reported in the January 2005 issue of "The American Journal of Clinical Nutrition" studied the effects of drinking oolong tea with either 22 mg or 690 mg of catechins on healthy men. After 12 weeks, the group who drank the 690 mg tea had lower body weight, body-mass index, or BMI, waist circumference, body fat mass, subcutaneous fat area and LDL compared to the group who consumed 22 mg.
References
- National Cancer Institute: Tea and Cancer Prevention: Strengths and Limits of the Evidence
- University of Maryland Medical Center: GreenTea
- "The Journal of Nutrition"; Mechanisms of Cancer Prevention by Tea Constituents; J. Lambert, et al.; October 2003
- "The American Journal of Clinical Nutrition"; Ingestion of a Tea Rich in Catechins Leads to a Reduction in Body Fat and Malondialdehyde-Modified LDL in Men; T. Nagao, et al.; January 2005
- "Archives of Internal Medicine"; Cholesterol-Lowering Effect of a Theaflavin-Enriched Green Tea Extract: A Randomized Controlled Trial; D.Maron, et al.; June 2003
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