More healing properties attributed to green tea
More healing properties attributed to green tea
Protection against skin cancer suggested
Green tea already is known for its powerful antioxidant properties and the resulting protection against several types of cancer. Now researchers at Case Western Reserve University in Cleveland are adding skin cancer to that list.
Whether green tea is consumed as a beverage or applied topically, it appears to provide strong protection against ultraviolet (UV) radiation, particularly against UV-B, the type that causes the most skin damage and the greatest risk of skin cancer, says Santosh Katiyar, PhD, senior research associate in dermatology at Case Western.1
"Green tea is a part of daily life for people in China, Japan, and Korea, and perhaps not coincidentally, skin cancer is far more rare there than it is in the United States," says Katiyar.
In fact, cancer onset in female Japanese patients who consume 10 cups of tea or more a day averages 8.7 years later, according to cancer researcher James Morre, PhD, professor of medicinal chemistry at Purdue University in West Lafayette, IN.
With 1.3 million new cases of skin cancer diagnosed every year, 47,700 of them deadly mela-nomas, there is a continuous search for greater skin protection, according to the American Cancer Society in Atlanta.
Recent research suggests that green tea’s health benefits are derived not only from its well-documented antioxidant properties, but also from anti-inflammatory properties and from the tea’s ability to prevent the growth of new blood vessels or angiogenesis, which is particularly significant in the development of tumors.
Polyphenolic compounds in green tea are at the heart of all three of those chemopreventive powers. The primary flavonoid polyphenol in green tea is (-)-epigallocathechin -3-gallate (EGCG), which along with three other epicatechins represent approximately 30% of green tea’s weight. A cup of green tea contains about 142 mg of EGCG.
Katiyar says green tea’s photoprotective benefits probably are best derived from topical application since it is targeted directly to the skin and provides immediate protection. One human study cited by Katiyar showed significantly less sunburn when subjects used a topical application of EGCG.
However, a study on hairless mice with green tea polyphenols added to their only drinking water source also showed significant protection against UV-inflicted skin damage.
What’s more, the polyphenols even shrank existing tumors in some animals.
Green tea is being added to popular health and beauty items, including toothpaste, shampoo, depilatory cream, facial cleansing lotion, moisturizing cream and lotion, scented sprays, body lotion, and bath and shower gels. Companies marketing green tea cosmetics include Avon and Estee Lauder in New York City; L’Oreal in Paris; Elizabeth Arden in Roanoke, VA; Carter-Wallace in New York City; Aubrey Organics in Tampa, FL; and Schwartzkopf in Compton, CA.
However, Katiyar notes, "Most if not all of these products are untested and are not standardized. The green tea polyphenols within these preparations are not uniform, yet the supplementation of skin products with green tea could have a profound impact on various skin disorders in the years to come."
Katiyar called for more research on the issue and said laboratory studies are currently in progress using human skin cells.
In an editorial accompanying Katiyar’s published study in the Archives of Dermatology, the call for physician awareness and for more research was repeated.
Noting extensive preclinical evidence of the efficacy of antioxidants such as green tea, vitamins C and E, garlic, and ginger, Gary S. Wood, MD, director of cutaneous oncology programs with the Department of Dermatology of University Hospitals of Cleveland, noted that clinical efficacy of green tea polyphenols has been demonstrated in human trials as well.
Remind patients of skin safety practices
"Dermatologists should be familiar with the effects of green tea polyphenols because of the large number of skin care products already containing these agents and the likelihood of additional products in the near future," Wood wrote in the editorial.
The American Cancer Society issued a statement noting that clinical evidence is not yet conclusive. The organization urges consumers to follow established skin safety practices:
• avoid long exposure to sun;
• wear sunscreens with an SPF of 15;
• wear sunglasses;
• avoid tanning beds and sun lamps.
In addition, Katiyar suggests particular attention be paid to wearing protective clothing and sunscreen between the hours of 11 a.m. to 2 p.m. when the sun’s rays are the strongest.
No negative side effects have been noted for green tea consumption except those normally associated with caffeine consumption. Green tea contains 6 mg to 30 mg of caffeine per cup, about one-third of the amount contained in black tea and 10% to 20% of that contained in coffee.
Standardized decaffeinated green tea extract also is available in capsules containing 97% green tea polyphenols under the brand name Tegreen, manufactured by Pharmanex Pharmaceuticals in San Francisco.
Like its cousins, black tea and oolong tea, green tea is made from the leaves of the Camellia sinensis, a hardy shrub most commonly grown in the Far East. It is pale in color, usually a subtle shade of light green or yellow, and the leaves are only lightly steamed or gently heated, a process which preserves the medicinally valuable polyphenolic compounds. Black tea, which comprises nearly 80% of the global tea production, is further processed, and the polyphenolic content is greatly reduced.
Other research credits green tea with additional health benefits, including cardioprotection, resistance to dental caries, improved cognitive performance, and maintained Crohn’s disease remission. Human research associates green tea consumption with lower rates of some cancers.
Among the strongest studies showing the benefits of tea drinking in general was derived from the Iowa Health Study, showing postmenopausal women who drank more than two cups of tea a day had a 10% lower incidence of all types of cancer compared to the general female population and 70% fewer gastrointestinal cancers and 40% fewer urinary cancers.3
Purdue’s Morre found an additional mechanism in green tea beyond its antioxidant properties. In a study on human mammary epithelial cells and HeLa cells derived from human cervical carcinoma, Morre found that EGCGs in green tea specifically target cancer cells. The EGCGs stop their cell division and growth, while leaving surrounding healthy cells unaffected. He attributes this characteristic to inhibition of the enzyme tNOX by EGCG.2
He found green tea infusions are approximately 10 times more effective than black tea and contain about 10 times more EGCG.
"Tea is one of the few agents that seem to inhibit cancer at all stages of development: initiation, promotion, and progression," he says. "It may not be accurate to think of tea simply as a good source of antioxidants."
Morre says his findings now provide a non-antioxidant mechanism linked to EGCG that may help explain the high degree of specificity of inhibition of the proliferation of several types of cancer cells. "We think this is really exciting because green tea is so safe and universal."
Morre says there is ongoing research on green tea, but large clinical trials are unlikely because green tea is nonproprietary. "So quite simply, no one wants to put up the money for the trials."
References
1. Katiyar S, Ahmad N, Mukhtar H. Green tea and skin. Arch Dermatol 2000; 136:989-994.
2. Morre D, Bridge A, Lian-Yang W et al. Preferential inhibition by (-)-epigallocatechin-3-gallate of the cell surface NADH oxidase and growth of transformed cells in culture. Biochem Pharm 2000: 60:937-946.
3. Zheng W, Doyle T, Kushi L et al. Tea consumption and cancer incidence in a prospective cohort study of postmenopausal women. Am J Epidemiol 1996; 144(2):175-182.
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