Both black and green teas are made from the same plant. The highest quality teas are derived from the young shoots comprising the first two or three leaves plus the growing bud; poorer quality teas are made from leaves located farther down the stems. Green tea is preferred as more of the active substances (catechins) remain in the less-processed green form. Green tea contains high levels of substances called polyphenols (catechins) known to possess strong antioxidant, anticarcinogenic, and even antibiotic properties. The four major green tea catechins are epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate (EGCg), the most potent and physiologically active antioxidant of the four catechins. A typical cup of green tea contains between 300 and 400 mg of polyphenols, of which 10 to 30 mg is EGCg.
Black tea contains theoflavins and theorubigins, which also inhibit cancer-promoting agents, and protects against oxidative damage.
A growing body of evidence in both human and animal studies suggests that regular consumption of green tea can reduce the incidence of a variety of cancers, including colon, pancreatic, and stomach cancers. Cancer inhibition seems to be related to anti-tumor activity by inhibiting urokinase (uPA, an enzyme used by human cancers to invade cells and spread), inhibiting angiogenesis (the formation of new blood vessels used by cancers to grow and spread), and possibly by inhibiting vascular endothelial growth factor, inhibition of an NADH oxidase known as quinol oxidase or NOX (NOX activity is needed for growth of normal cells, and an overactive form of NOX called tNOX allows tumor cells to grow; EGCg inhibits tNOX but not NOX).
Also, giving green tea with the chemotherapy drug doxorubicin decreased heart toxicity often seen with doxorubicin administration (by decreasing doxorubicin concentration in heart cells) and increased doxorubicin concentration in cancer cells.
Green tea has also been shown to maintain white blood cell counts in human patients undergoing radiation or chemotherapy.
Other proposed benefits of green tea include: reduced cholesterol and triglycerides, arterial relaxation (via an increase in nitric oxide and intracellular calcium), inhibition of platelet clumping (via the amino acid theanne in the tea, which inhibits thromboxane), immune enhancement (by increased production of B-cells), treating infections (by inhibiting bacterial enzymes and inhibiting viral absorption onto cell membranes), possible lower blood sugar in diabetic pets (although one study has made the assertion that regular consumption of tea by children increases their development of diabetes), antioxidant activity (increased levels of seroxide dismutase in the blood and increased activity of glutathione S-transferase and catalase in the liver), liver protection, and kidney protection.
While the observational preclinical studies used to draw these conclusions (both experimental laboratory testing in lab animals and in vitro studies) support the health benefits of tea (especially green tea), studies in people have been misleading and do not always show consistent results. Epidemiological studies have turned up both positive and negative results on the health benefits of green tea; not everyone who examines the data concludes that green tea has been proven effective. However, most doctors feel there are health benefits to the use of green tea despite the inconclusive clinical studies.
Studies suggest people drinking three cups of green tea daily have increased protection against cancer. The typical consumption of green tea in the average Japanese tea drinker is ten cups per day (1000 mg of EGCg daily). However, because not everyone wants to take the time to drink green tea, manufacturers have offered extracts that can be taken in pill form. A typical dosage is 100 to 150 mg three times daily of a green tea extract standardized to contain 80 percent total polyphenols and 50 percent epigallocatechin gallate. Whether these extracts work as well as the real thing remains unknown, although some studies have shown effectiveness. Since pets will not drink this much tea each day, and it is unknown whether the extracts are effective, the use of green tea in pets to prevent cancer is still unproven. Because the results of most tests appear encouraging, many veterinarians are supportive of the use of green tea for pets with a variety of medical disorders, especially cancer.
Black tea applied topically appears to soothe discomfort in the mouth that is associated with radiation-induced damage (radiation mucositis). Applying black or green tea to pets with gingivitis or oral ulcerations may be soothing.
Black and green teas are generally regarded as safe. Green tea does contain caffeine, although at a lower level than black tea or coffee, and can therefore cause insomnia, nervousness, and the other well-known symptoms of excess caffeine intake. Due to the potential for platelet inhibition and increased bleeding, pets taking anticoagulant medications such as aspirin must be monitored carefully for bleeding. EGCg has provoked asthmatic attacks in a small number of asthmatic patients working in a tea factory. Tea has a low sodium but high potassium content; pets with elevated potassium levels (end-stage kidney failure) should not take green tea. Green tea should not be given to infants and young children as it may cause iron metabolism problems and microcytic anemia; similar precautions probably apply in pets. For pets taking MAO inhibitors, the caffeine in green tea could cause serious problems.
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Shawn Messonnier, DVM
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Shawn Messonnier DVM Past Supporting Member, Oncology Association of Naturopathic Physicians Author, the award-winning The Natural Health Bible for Dogs & Cats, The Natural Vet’s Guide to Preventing and Treating Cancer in Dogs, and Breast Choices for the Best Chances: Your Breasts, Your Life, and How YOU Can Win The Battle!
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