Black, oolong, white and green teas are all produced from the same Camellia sinensis plant, which is native to eastern Asia but also grown in other areas. The Camellia sinensis leaves and leaf buds are used to produce various types of teas. Green tea is prepared by steaming and pan-frying these leaves and then drying them. Black tea is produced by a complex wilting and fermentation process. Other teas such oolong involve processes in which the leaves are totally fermented (black tea) or partially fermented (oolong tea).
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Genital Warts: A specific green tea extract ointment (Veregen, Bradley Pharmaceuticals; Polyphenon E ointment 15%, MediGene AG) is FDA-approved for treating genital warts. Applying the ointment for 10-16 weeks seems to clear these types of warts in 24% to 60% of patients.
High Cholesterol: People who consume higher amounts of green tea appear to have lower levels of Total cholesterol, low-density lipoprotein (LDL or "bad") cholesterol, and triglycerides, as well as higher levels of high-density lipoprotein (HDL or "good") cholesterol. Consuming green tea or taking green tea extract containing 150 to 2500 mg of green tea catechins, an antioxidant found in green tea, daily for up to 24 weeks has been shown to reduce Total and LDL cholesterol in people with high levels of blood fats or cholesterol.
Cervical Dysplasia (abnormal development of cells of the cervix): Taking green tea by mouth or applying it to the skin may reduce cervical dysplasia caused by human papilloma virus (HPV) infection.
Coronary Artery Disease (clogged arteries): Population studies suggest that drinking green tea is linked to a reduced risk of clogged arteries. The link seems to be stronger in men than women.
Endometrial Cancer: Population studies suggest that drinking green tea is linked to a reduced risk of developing endometrial cancer.
High Blood Pressure: There is some conflicting evidence about the effects of tea on high blood pressure. Population research in Chinese people shows that drinking 120-599 mL of green tea or oolong tea daily is linked to a lower risk of developing high blood pressure. Drinking more than 600 mL daily is linked to an even lower risk. Also, early clinical research suggests that taking green tea extract daily for 3 months, or drinking green tea three times per day for 4 weeks, reduces blood pressure in people with high blood pressure. Analysis of clinical research shows that green tea can reduce systolic blood pressure (the top number) by up to 3.2 mmHg and diastolic blood pressure (the bottom number) by up to 3.4 mmHg in people with or without high blood pressure. But several smaller studies show that green and black tea have no effect on blood pressure.
Low Blood Pressure: Drinking green tea might help increase blood pressure in elderly people who have low blood pressure after eating.
Oral Leukoplakia (thick, white patches on the gums): Drinking green tea has been shown to decrease the size of white patches in people with oral leukoplakia.
Osteoporosis: A population study suggests that drinking green tea for 10 years is linked to increased bone mineral density. Also, early research suggests that taking a green tea compound, containing 500 mg of catechins, twice daily for 24 weeks improves bone strength in post-menopausal women with low bone density.
Ovarian Cancer: Women who regularly drink tea, including green and black tea, appear to have a lower risk of developing ovarian cancer. Green tea, however, does not seem to prevent ovarian cancer from recurring in people with a history of ovarian cancer.
Parkinson's Disease: Drinking one to four cups of green tea daily appears to provide the most protection against developing Parkinson's disease.
Green tea is LIKELY SAFE for most adults when consumed as a drink in moderate amounts, or when green tea extract is applied to the skin as a specific ointment (Veregen, Bradley Pharmaceuticals), short-term.
Green tea extract is POSSIBLY SAFE for most people when taken by mouth for up to 2 years, when applied to the skin as other ointments short-term, or when used as a mouthwash short-term. In some people, green tea can cause stomach upset and constipation. In rare cases, green tea extracts have been reported to cause liver problems.
Green tea is POSSIBLY UNSAFE when taken by mouth long-term or in high-doses. It can cause side effects due to the caffeine. These side effects range from mild to serious and include headache, nervousness, sleep problems, vomiting, diarrhea, irritability, irregular heartbeat, tremor, heartburn, dizziness, ringing in the ears, convulsions, and confusion. Green tea may also reduce the absorption of iron from food.
Drinking very high doses of green tea is LIKELY UNSAFE and can actually be fatal. The fatal dose of caffeine in green tea is estimated to be 10-14 grams (150-200 mg per kilogram of body weight). Serious toxicity can occur at higher doses.
Children: Green tea is POSSIBLY SAFE for children when used in amounts commonly found in foods and beverages or when used for gargling three times daily for up to 90 days.
Pregnancy and breast-feeding: If you are pregnant or breast-feeding, green tea in small amounts - about 2 cups per day - is POSSIBLY SAFE. This amount of green tea provides about 200 mg of caffeine. However, drinking more than 2 cups of green tea per day is POSSIBLY UNSAFE. Consuming more than 2 cups of green tea daily has been linked to an increased risk of miscarriage and other negative effects due to the caffeine content. Also, green tea might increase the risk of birth defects associated with folic acid deficiency. In women who are nursing, caffeine passes into breast milk and can affect a nursing infant. Do not drink an excessive amount of green tea if you are pregnant or breast-feeding.
Anemia ("tired blood"): Drinking green tea may make anemia worse.
Anxiety Disorders: The caffeine in green tea might make anxiety worse.
Bleeding Disorders: Caffeine in green tea might increase the risk of bleeding. Don't drink green tea if you have a bleeding disorder.
Heart Conditions: Caffeine in green tea might cause irregular heartbeat.
Diabetes: Caffeine in green tea might affect blood sugar control. If you drink green tea and have diabetes, monitor your blood sugar carefully.
Diarrhea: Green tea contains caffeine. The caffeine in green tea, especially when taken in large amounts, can worsen diarrhea.
Glaucoma: Drinking green tea increases pressure inside the eye. The increase occurs within 30 minutes and lasts for at least 90 minutes.
High Blood Pressure: The caffeine in green tea may increase blood pressure in people with high blood pressure. However, this does not seem to occur in people who regularly drink green tea or other products that contain caffeine.
Irritable Bowel Syndrome (IBS): Green tea contains caffeine which, when taken in large amounts, can worsen diarrhea and may worsen symptoms of IBS.
Liver Disease: Green tea extract supplements have been linked to several cases of liver damage. Green tea extracts might make liver disease worse.
Osteoporosis (weak bones): Drinking green tea can increase the amount of calcium that is flushed out in the urine. Caffeine should be limited to less than 300 mg per day (approximately 2-3 cups of green tea). It is possible to make up for some calcium loss caused by caffeine by taking calcium supplements, or consuming foods high in calcium such as cooked, leafy green vegetables, tofu, beans and fortified foods (cereals, juice and non-dairy milks).
Stimulant drugs such as amphetamines speed up the nervous system. By speeding up the nervous system, stimulant medications can make you feel jittery and increase your heart rate. The caffeine in green tea may also speed up the nervous system, therefore consuming green tea along with stimulant drugs might cause serious problems including increased heart rate and high blood pressure. Avoid taking stimulant drugs along with caffeine.
Stimulant drugs such as cocaine speed up the nervous system. By speeding up the nervous system, stimulant medications can make you feel jittery and increase your heart rate. The caffeine in green tea might also speed up the nervous system. Taking green tea along with stimulant drugs might cause serious problems including increased heart rate and high blood pressure. Avoid taking stimulant drugs along with caffeine.
Stimulant drugs speed up the nervous system. Caffeine (contained in green tea) and ephedrine are both stimulant drugs. Taking green tea along with ephedrine might cause too much stimulation and sometimes serious side effects and heart problems. Do not take caffeine-containing products and ephedrine at the same time.
Green tea contains caffeine which may block the effects of adenosine (Adenocard). Adenosine is often used by doctors to do a test on the heart called a cardiac stress test. Stop consuming green tea or other caffeine-containing products at least 24 hours before a cardiac stress test.
The body breaks down caffeine to get rid of it. Some antibiotics might decrease how quickly the body breaks down this caffeine. Taking these antibiotics along with green tea can increase the risk of side effects including jitteriness, headache, increased heart rate, and other side effects.
Some antibiotics that decrease how quickly the body breaks down caffeine include ciprofloxacin (Cipro), enoxacin (Penetrex), norfloxacin (Chibroxin, Noroxin), sparfloxacin (Zagam), trovafloxacin (Trovan), and grepafloxacin (Raxar).
Birth control pills can decrease how quickly the body breaks down caffeine. Taking green tea along with birth control pills can cause jitteriness, headache, fast heartbeat, and other side effects.
Some birth control pills include ethinyl estradiol and levonorgestrel (Triphasil), ethinyl estradiol and norethindrone (Ortho-Novum 1/35, Ortho-Novum 7/7/7), and others.
Cimetidine (Tagamet) can decrease how quickly your body breaks down caffeine. Taking cimetidine along with green tea may increase the chance of caffeine side effects including jitteriness, headache, fast heartbeat, and others.
The body breaks down clozapine (Clozaril) to get rid of it. The caffeine in green tea appears to decrease how quickly the body breaks down clozapine. Taking green tea along with clozapine can increase its effects and side effects [of clozapine].
The caffeine in green tea may block the effects of dipyridamole (Persantine). Dipyridamole is often used by doctors to do a test on the heart called a cardiac stress test. Stop drinking green tea or other caffeine-containing products at least 24 hours before a cardiac stress test.
Disulfiram (Antabuse) can decrease how quickly the body gets rid of caffeine. Taking green tea (which contains caffeine) along with Disulfiram might increase the effects and side effects of caffeine including jitteriness, hyperactivity, irritability, and others.
Estrogens can decrease how quickly the body breaks down caffeine. Taking estrogen pills and drinking green tea can cause jitteriness, headache, fast heartbeat, and other side effects. If you take estrogen pills limit your caffeine intake.
Some estrogen pills include conjugated equine estrogens (Premarin), ethinyl estradiol, estradiol, and others.
The body breaks down the caffeine in green tea to get rid of it. Fluvoxamine (Luvox) can decrease how quickly the body breaks down caffeine. Taking green tea along with fluvoxamine may lead too high levels of high caffeine in the body, and increase its effects and side effects.
Your body naturally gets rid of lithium, however caffeine in green tea may increase how quickly your body gets rid of it. If you take products that contain caffeine and you take lithium, stop taking caffeine products slowly. Stopping caffeine too quickly may increase the side effects of lithium.
The caffeine in green tea can stimulate the body. Some medications used for depression can also stimulate the body. Drinking green tea and taking some medications for depression might cause too much stimulation of the body and serious side effects including fast heartbeat, high blood pressure, nervousness, and others.
Some of these medications used for depression include phenelzine (Nardil), tranylcypromine (Parnate), and others.
Green tea extracts might harm the liver. Taking green tea extracts along with medication that might also harm the liver can increase the risk of liver damage. Do not take green tea extracts if you are taking a medication that can harm the liver.
Some medications that can harm the liver include acetaminophen (Tylenol and others), amiodarone (Cordarone), carbamazepine (Tegretol), isoniazid (INH), methotrexate (Rheumatrex), methyldopa (Aldomet), fluconazole (Diflucan), itraconazole (Sporanox), erythromycin (Erythrocin, Ilosone, others), phenytoin (Dilantin), lovastatin (Mevacor), pravastatin (Pravachol), simvastatin (Zocor), and many others.
Green tea may slow blood clotting. Taking green tea along with medications that also slow clotting might increase the chances of bruising and bleeding.
Some medications that slow blood clotting include aspirin, clopidogrel (Plavix), diclofenac (Voltaren, Cataflam, others), ibuprofen (Advil, Motrin, others), naproxen (Anaprox, Naprosyn, others), dalteparin (Fragmin), enoxaparin (Lovenox), heparin, warfarin (Coumadin), and others.
Stimulant drugs such as nicotine speed up the nervous system. By speeding up the nervous system, stimulant medications can make you feel jittery and increase your heart rate. The caffeine in green tea might also speed up the nervous system, therefore consuming green tea along with stimulant drugs may cause serious problems including increased heart rate and high blood pressure. Avoid taking stimulant drugs along with caffeine.
The stimulant effects of the caffeine in green tea can block the sleep-producing effects of pentobarbital.
Phenylpropanolamine, as well as the caffeine in green tea can stimulate the body. Taking green tea and phenylpropanolamine together might cause too much stimulation and increase heartbeat, blood pressure and cause nervousness.
The body breaks down riluzole (Rilutek) to get rid of it. Drinking green tea can decrease how quickly the body breaks down riluzole and increase the effects and side effects of riluzole.
Caffeine works similarly to theophylline, however it may decrease how quickly the body gets rid of theophylline. Taking green tea along with theophylline might increase its effects and side effects [of theophylline].
The body breaks down the caffeine in green tea to get rid of it. Verapamil (Calan, Covera, Isoptin, Verelan) can decrease how quickly the body gets rid of caffeine. Drinking green tea and taking verapamil (Calan, Covera, Isoptin, Verelan) can increase the risk of side effects for caffeine including jitteriness, headache, and an increased heartbeat.
Warfarin (Coumadin) is used to slow blood clotting. Large amounts of green tea have been reported to decrease the effectiveness of warfarin, which may increase the risk of clotting. It is unclear why this interaction might occur, so be sure to have your blood checked regularly. The dose of your warfarin might need to be changed.
Alcohol can decrease how quickly the body breaks down caffeine. Consuming green tea along with alcohol may lead to high levels of caffeine in the bloodstream and increased side effects including jitteriness, headache, and fast heartbeat.
Fluconazole (Diflucan) might decrease how quickly the body gets rid of caffeine and cause caffeine to stay in the body for too long. Taking fluconazole along with green tea may increase the risk of side effects such as nervousness, anxiety, and insomnia.
Caffeine has been shown to increase blood sugar. Diabetes medications are used to lower blood sugar, therefore taking some medications for diabetes along with caffeine may decrease its effectiveness. Monitor your blood sugar closely - the dose of your diabetes medication may need to be changed.
Some medications used for diabetes include glimepiride (Amaryl), glyburide (DiaBeta, Glynase PresTab, Micronase), insulin, pioglitazone (Actos), rosiglitazone (Avandia), chlorpropamide (Diabinese), glipizide (Glucotrol), tolbutamide (Orinase), and others.
Mexiletine (Mexitil) can decrease how quickly the body breaks down caffeine. Taking Mexiletine along with green tea might increase the caffeine effects and side effects of green tea.
Terbinafine (Lamisil) can decrease how fast the body gets rid of caffeine. Drinking green tea along with terbinafine can increase the risk of caffeine side effects including jitteriness, headache, increased heartbeat, and other effects.
The United Kingdom Tea Council recommends drinking not more than 6 cups of tea a day. For the best health benefits, 3 to 4 cups are recommended. However, doses of green tea vary significantly - usually a range of 1-5 cups daily is considered safe. The commonly used dose of green tea is based on the amount typically consumed in Asian countries, which is about 3 cups per day, providing 240-320 mg of the active ingredients, polyphenols. To make tea, people typically use 1 tsp of tea leaves in 8 ounces of near boiling water.
Drink green tea when it’s freshly made but slightly cooled. Scalding tea can damage your digestive system. Moreover, recent studies suggest that too much hot tea can promote throat cancer. Compounds in tea like catechins, theanine, and vitamins C and B diminish over time through oxidation, so the health benefits are strongest with fresh tea. If you’re brewing the same tea leaves, brew them in moderation. With each successive infusion, potentially harmful substances in the leaves themselves (often pesticides) are drawn out and may be toxic. Old tea can also harbor bacteria, especially since its antibacterial properties diminish with time.
You don’t have to quit drinking your favorite cup of green tea, but if you have any of the above mentioned medical conditions or are taking prescription drugs, exercise caution and consult your doctor about how many cups you may consume per day. Moderation is the key to enjoying the full benefits of green tea. :)
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