Green tea is not usually prescribed as a remedy for diseases. However, people all over the world have noticed that drinking green tea daily has many health benefits. Green tea is an important preventative against cancer, elevated blood fats, hardening of the arteries, and dental cavities. It also protects against bacterial dysentery. Green tea can help ward off a number of fungal, bacterial, and even viral infections (like the common cold) as well. Green tea is also good for your digestive system. It may help you think more clearly, and may even improve your eyesight. Green tea strengthens arteries, lowers cholesterol, and reduces excess fats in the blood. It clears phlegm from sore throats, and neutralizes poisons. The tannins in green tea can stop diarrhea. If you want to increase the tannin levels in your tea, let it brew longer. Some preliminary studies also suggest that green tea extract may boost metabolism and help burn fat.

One of the active compounds in green tea is as effective as aspirin in keeping blood platelets from clumping together, which improves circulation and may prevent against hardening of the arteries. Population studies show that there's less cancer in countries where people drink green tea every day, but no cause and effect has been established. Black tea does not have the same effect. In fact, if you drink a lot of black tea, you increase your risk for getting cancers of the rectum, gallbladder, and endometrium. Green tea is highly recommended as an alternative to coffee and black tea. Green tea's cancer-fighting effects work best against gastrointestinal cancer, lung cancer, and breast cancer. Studies on the effects of green tea on colon or rectal cancer have produced conflicting results. Some studies show decreased risk in those who drink the tea, while others show increased risk.

The difference between green and black teas is in their processing. The fresh leaves are slightly steamed and then quickly dried in green tea. This prevents enzymes in the tea from breaking down nutritious substances called polyphenols, which are the cancer-fighting compounds in green tea. Green tea polyphenols (GTP) are even better antioxidants than vitamins C and E.

The tea plant is a large shrub with evergreen leaves. It originally came from China, where it has been used for more than 5,000 years. Today, tea is grown throughout Asia and parts of the Middle East and Africa. Black tea is more common in the United States. But black tea is fermented and not as healthy as green tea. Green tea is unfermented. (Oolong tea is semi-fermented.)

The leaf buds and young leaves make the best green tea. Tea contains the purine alkaloids caffeine, theophylline, and theobromine. The most important active ingredients are polyphenols, which are responsible for many of the therapeutic and preventive actions of green tea.

Most green tea products are sold as dried leaf tea. There are also extracts made from the leaves and leaf buds. Green tea has 300 to 400 polyphenols and 50 to 100 mg caffeine per cup. Decaffeinated green tea products contain concentrated polyphenols (60 to 89% total polyphenols).

Pediatric

There are no reports to date about the use of green tea in children. Therefore, use of this herb in children is not recommended at this time.

Adult

Three cups of green tea per day (3 g soluble components, or 240 to 320 g polyphenols) or 300 to 400 mg per day of standardized green tea extract (extracts should contain 80% total polyphenols and 55% epigallocatechin) is the recommended dosage. Capsules and liquid preparations are also available.

Limit your intake of green tea if you have a sensitive stomach, cardiovascular complications, kidney disorder, overactive thyroid, or tendency toward spasm. If you're prone to anxiety attacks, be careful drinking tea or any caffeinated beverage.

If you're pregnant, don't ingest any products that contain caffeine, including tea. If you must have tea, try to limit yourself to no more than 3 cups of green tea per day. This is a maximum of 200 mg of caffeine per day. And drink your tea over the course of the entire day (but not too late at night). Don't drink it all in a short period of time. You should also avoid tea if you're nursing. Even a small amount of caffeine might give your baby a sleeping disorder.

If you take more than 1.5 g of tea every day over a long period of time, you might develop serious symptoms. This much caffeine can cause irritability, insomnia, heart palpitation, and dizziness. You may experience vomiting, diarrhea, and headaches, and you might lose your appetite. If you are drinking a lot of tea and start to vomit or have abdominal spasms, you may have caffeine poisoning. Lower your caffeine intake and see your health care provider if your symptoms are severe. The side effects of drinking too much tea are usually not fatal.

Green tea may increase the effectiveness of beta-lactam antibiotics by reducing bacterial resistance to treatment. Consult your healthcare provider before using green tea if you are currently taking these antibiotics.

The combination of green tea and chemotherapy medications, specifically doxorubicin and tamoxifen, increased the effectiveness of these medications in laboratory studies. These results have not yet been demonstrated in studies with human subjects. You should consult with your healthcare provider before using green tea if you are currently being treated with either doxorubicin or tamoxifen.

Green tea should not be taken with warfarin, a blood-thinning medication. Green tea contains vitamin K, which diminishes the effects of warfarin. There has been at least one report of an interaction between these substances that decreased the effectiveness of warfarin. If you are currently taking warfarin, you have probably been counseled to minimize your intake of substances containing vitamin K, including green tea.

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