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Tea Contains Health-Promoting Polyphenols
Posted by SoundHealth, in Nutrition
Topics: Tea Green Tea Polyphenols

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From green, black and white, teas are packed full of flavonoids and other health beneficial antioxidants. Studies have associated some teas with relieving conditions like cancer, heart disease, and diabetes; encouraging weight loss; and bringing about mental alertness.

"tea" can refer to any number of beverages including herbals like mint or chamomile. But 'true' tea that is packed with beneficial antioxidants is made from the leaves, stems and buds of the Camellia sinensis plant. This includes the varieties black, green, white or oolong tea, which all come from this bush. The difference between the teas is how they are processed. "green tea" is made from leaves that are dried right after harvesting, while the leaves used to make black tea are fermented for a short time. White tea leaves do not undergo any oxidation and are shielded from the sun and not allowed to produce any chlorophyll.

Health Benefits of Tea

Tea is a good source of flavonoids called catechins, which are important antioxidants that are associated with helping to prevent certain diseases. The majority of these catechins are found in green tea and include epigallocatechin-3-gallate (EGCG), the most abundant and widely studied tea polyphenol.

All of these teas contain caffeine and theanine (an amino acid), which affect the brain, and have shown to heighten mental alertness. Caffeine levels tend to be higher in tea bag forms (the finer grind releases more caffeine).

The more processed the tea leaves, usually the less polyphenol content. As oolong and black teas are oxidized or fermented, they have lower concentrations of polyphenols than green tea; but their antioxidizing power is still high.

Here's what some studies have found about the potential health benefits of tea:

Green tea: Made with steamed tea leaves, it has a high concentration of EGCG and has been widely studied. The antioxidants in green tea as associated with relieving conditions varying from simple viral or bacterial infections, to degenerative conditions including cancer, cardiovascular disease, stroke, osteoporosis and periodontal disease. Green tea has also shown to alleviate symptoms of illnesses such as diabetes, liver disease and arthritis.

Black tea: Made with fermented tea leaves, black tea has the highest caffeine content and forms the basis for flavored teas like chai, along with some instant teas. Studies have linked the consumption of black tea along with green tea in helping to reduce the risk of heart disease, by improving endothelial function (keeping the lining of the arteries open to allow more blood flow) and lowering blood pressure. The major polyphenols of black tea and green tea have also been shown to inhibit proteins which are closely associated with cancer tumor growth and metastasis (the spreading of cancer cells from one organ or tissue to another).

White tea: This is uncured and unfermented tea, and one study showed that white tea has the most potent anticancer properties compared to more processed teas.

Boosts insulin activity: a study from the US found that green, black and oolong teas increased insulin activity by about fifteen-fold in tests using fat cells obtained from rats.

Weight loss: Preliminary research findings suggest that drinking tea has an effect on weight and fat accumulation in the body. Researchers found that green tea extract significantly increased energy expenditure and fat oxidation, and resulted in weight loss of modestly obese patients.

Herbal Teas

Herbal tea is not really tea; it is an infusion of herbs, fruits, flowers, seeds, or roots. As these infusions do not come from the Camellia plant, they therefore do not have its health promoting benefits. Their chemical compositions of herbal infusions vary widely depending on the plant used, but they do promote various other health qualities, and have relaxing and calming effects. Another advantage is that they are caffeine-free.

Common varieties include: ginger, chamomile, ginkgo biloba, ginseng, hibiscus, jasmine, rosehip, mint, rooibos (red tea), and echinacea.

Limited research has been done on the health benefits of herbal teas, but here are some of the findings:

Chamomile tea: Its antioxidants are associated with helping prevent complications from diabetes, like loss of vision and nerve and kidney damage, and stunt the growth of cancer cells.

Hibiscus tea: A small study found that drinking three cups of hibiscus tea daily lowered blood pressure in people with modestly elevated levels.

Rooibos (red tea): This is a South African herb that is fermented. Although it has flavonoids with cancer-fighting properties, medical studies have been limited.

Tips on Using Tea

  • Instant tea generally contains very little amounts of actual tea and therefore out of all the forms of tea, it has the least amount of health-promoting catechins.

  • Green and white teas are best brewed at lower temperatures (around 80 degrees Fahrenheit), because if the water is too hot the leaves will burn, leaving a bitter taste.

  • Black tea should be allowed to steep for about five minutes for the best flavor, and eighty percent of the catechins are released by the five-minute mark.

References

  • Henning SM, Niu Y, Lee NH, Thames GD, Minutti RR, Wang H, Go VLW, Heber D. Bioavailability and antioxidant activity of tea flavonols after consumption of green tea, black tea, or a green tea extract supplement. Am J Clin Nutr. 2004;80:1558-1564.

  • Arts IC, Jacobs DR Jr, Gross M, et al. Dietary catechins and cancer incidence among postmenopausal women: the Iowa Womens health Study (United States). Cancer Causes Control. 2002;13(4):373-382.

  • Conney AH, Lu Y, Lou Y-R, et al. Inhibitory effect of green and black tea on tumor growth. Proc Soc Exp Biol Med. 1999;220:229-233.

  • Hakim IA, Harris RB. Joint effects of citrus peel use and black tea intake on the risk of squamous cell carcinoma of the skin. BMC Dermatol. 2001;1:3.

  • Dora I, Arab L, Martinchik A, et al. Black tea consumption and risk of rectal cancer in Moscow population. Ann Epidemiol. 2003;13(6):405-411

  • Isemura M, Saeki K, Kimura T, et al. Tea catechins and related polyphenols as anti-cancer agents. Biofactors. 2000;13(1-4):81-85.

  • Cabrera C, Artacho R, Gimenez R. Beneficial effects of green tea--a review. J Am Coll Nutr. 2006 Apr;25(2):79-99. Review.

  • Yang YC, Lu FH, Wu JS, et al. The protective effect of habitual tea consumption on hypertension. Arch Intern Med. 2004;164(14):1534-1540.

  • Arts ICW, Hollman PCH, Feskens EJM, Bueno de Mesquita HB, Kromhout D. Catechin intake might explain the inverse relation between tea consumption and ischemic heart disease: The Zutphen Elderly Study. Am J Clin Nutr. 2001;74:227-232.

  • Nagao T, Komine Y, Soga S, Meguro S, Hase T, Tanaka Y, and Tokimitsu I. Ingestion of a tea rich in catechins leads to a reduction in body fat and malondialdehyde-modified LDL in men. Am J Clin Nutr.2005;81:122-129.

  • Hegarty VM, May HM, Khaw K-T. Tea drinking and bone mineral density in older women. Am J Clin Nutr 2000;71:1003-7.

  • Anderson RA, Polansky MM. Tea enhances insulin activity.J Agric Food Chem. 2002 Nov 20;50(24):7182-6.


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