Tea

All types of tea—green, black, oolong, and white—are produced from the Camellia sinensis plant using different methods. Tea is usually brewed and drunk as a beverage, but green tea extracts are also sold in capsules and sometimes used in skin products. (Herbal teas are made from plants other than Camellia sinensis.) 

Tea contains various components, including polyphenols, alkaloids (caffeine, theophylline, and theobromine), amino acids, carbohydrates, proteins, chlorophyll, volatile organic compounds (chemicals that readily produce vapors and contribute to the aroma of tea), fluoride, aluminum, minerals, and trace elements. The polyphenols are thought to be responsible for the health benefits that have traditionally been attributed to tea, especially green tea. 

Green tea is often promoted for improving mental alertness, relieving digestive symptoms and headaches, and stimulating weight loss. Also, green tea and its extracts have been studied for their possible protective effects against heart disease and cancer. 

So far, we have learned the following about tea: 

• Although tea and/or tea polyphenols have been found in animal studies to inhibit the growth of tumors in different parts of the body, the results of human studies—both epidemiologic and clinical studies—have been inconclusive.  
• Green tea has not been shown to be effective for weight loss.  
• Very few long-term studies have looked at the effects of tea on heart disease risk. However, the limited evidence currently available suggests that both green and black tea might have beneficial effects on some heart disease risk factors, including blood pressure and cholesterol.

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