- What other names is Green Tea known by?
- What is Green Tea?
- Is Green Tea effective?
- How does Green Tea work?
- Are there safety concerns?
- Are there any interactions with medications?
- Dosing considerations for Green Tea.
Green Tea Safety and Side Effects
Green tea is safe for most adults. Green tea extract seems to be safe for most people for short-term use. In some people, green tea can cause stomach upset and constipation. Green tea extracts have been reported to cause liver problems.
Too much green tea, such as more than five cups per day, can cause side effects because of the caffeine. These side effects can 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 seems to reduce the absorption of iron from food.
If you are pregnant or breastfeeding, green tea in small amounts is probably not harmful. Do not drink more than 2 cups a day of green tea. This amount of tea provides about 200 mg of caffeine. Consuming more than this amount has been linked to an increased risk of miscarriage and other negative effects...
Green tea is used to improve mental alertness and thinking.
It is also used for weight loss and to treat stomach disorders, vomiting, diarrhea, headaches, bone loss (osteoporosis), and solid tumor cancers.
Some people use green tea to prevent various cancers, including breast cancer, prostate cancer, colon cancer, gastric cancer, lung cancer, solid tumor cancers and skin cancer related to exposure to sunlight. Some women use green tea to fight human papilloma virus (HPV), which can cause genital warts, the growth of abnormal cells in the cervix (cervical dysplasia), and cervical cancer.
Green tea is also used for Crohn's disease, Parkinson's disease, diseases of the heart and blood vessels, diabetes, low blood pressure, chronic fatigue syndrome (CFS), dental cavities (caries), kidney stones, and skin damage.
Instead of drinking green tea, some people apply green tea bags to their skin to soothe sunburn and prevent skin cancer due to sun exposure. Green tea bags are also used to decrease puffiness under the eyes, as a compress for tired eyes or headache, and to stop gums from bleeding after a tooth is pulled.
Green tea in candy is used for gum disease.
Green tea is used in an ointment for genital warts. Do not confuse green tea with oolong tea or black tea. Oolong tea and black tea are made from the same plant leaves used to make green tea, but they are prepared differently and have different medicinal effects. Green tea is not fermented at all. Oolong tea is partially fermented, and black tea is fully fermented.
There isn't enough information to know if green tea is effective for the other conditions people use it for including: kidney disease, heart disease, kidney stones, tooth decay, and others.
Likely Effective for...
- Genital warts. A specific green tea extract ointment (Veregen, Bradley Pharmaceuticals) is FDA-approved for treating genital warts.
- High cholesterol. Taking green tea by mouth seems to lower cholesterol levels. Research suggests that consuming 145-3000 mg of green tea catechins, an antioxidants found in green tea, daily for up to 24 weeks reduces total cholesterol and low-density lipoprotein (LDL or "bad") cholesterol.
- Mental alertness. Drinking green tea and other caffeinated beverages seems to help people maintain mental alertness throughout the day. Combining caffeine with sugar as an "energy drink" seems to improve mental performance more than caffeine or sugar alone. Also, taking a combination of green tea extract and L-theanine for seems to improve memory and attention in people with mild mental problems.
Possibly Effective for...
- Abnormal development of cells of the cervix (cervical dysplasia). Taking green tea by mouth or applying it to the skin seems to reduce cervical dysplasia caused by human papilloma virus (HPV) infection.
- Clogged arteries (coronary artery disease). 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.
- Low blood pressure. Drinking green tea might help increase blood pressure in elderly people who have low blood pressure after eating.
- Thick, white patches on the gums (oral leukoplakia). Drinking green tea seems to decrease the size of white patches in people with oral leukoplakia.
- Osteoporosis. Research 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, an antioxidant in green tea, daily for 24 weeks improves bone strength in post-menopausal women with low bone density.
- Ovarian cancer. Women who regularly drink tea, including green or black tea, appear to have a lower risk of developing ovarian cancer.
- Parkinson's disease. Drinking one to four cups of green tea daily seems to provide the most protection against developing Parkinson's disease.
Insufficient Evidence to Rate Effectiveness for...
- Acne. Early research suggests that applying a solution containing a certain chemical found in green tea to the skin for 8 weeks reduces acne.
- Abnormal protein buildup in the organs (Amyloidosis). Early research suggests that drinking green tea or taking green tea extracts for 12 months protects against an increase in heart mass in people with amyloidosis affecting the heart.
- Athletic performance. There is inconsistent evidence about the effects of green tea on athletic performance. Some early research suggests that taking green tea extract as a beverage does not improve breathing or performance in people undergoing endurance training. However, other early research suggests that taking seven doses of a certain green tea chemical over three days improves some breathing tests in healthy adults.
- Bladder cancer, esophadeal cancer, and pancreatic cancer. Most evidence suggests that drinking green tea is linked to a lower risk of bladder, esophageal, and pancreatic cancer. However, there is also some inconsistent evidence that suggests it might not reduce the risk of developing these cancers.
- Breast cancer. Research suggests that green tea does not seem to reduce the risk of breast cancer in Asian people. However, there is some evidence that it might reduce the risk in Asian-Americans.
- Heart disease. Population studies suggest that drinking three or more cups of green tea daily is linked to a decreased risk of death from heart disease or any cause.
- Colds and flu. Early research suggests that taking a specific formulation of green tea and theanine (Thea-flan and Suntheanine) daily for 5 months lowers the risk of developing the flu. Other early research suggests that taking a specific green tea product (ImmuneGuard) reduces cold and flu symptoms and the duration of illness.
- Colon cancer. Most evidence suggests that drinking green tea does not have any effect on colon cancer risk. However, some research suggests that consuming a high amount is linked to a reduce risk, particularly in women.
- Diabetes. Research suggests that Japanese adults, particularly women, who drink 6 or more cups of green tea daily, have a lower risk of developing diabetes. However, green tea extract does not seem to help control sugar or insulin levels in people who already have diabetes.
- Fertility. Early research suggests that taking a specific product containing chasteberry, green tea, L-arginine, vitamins and minerals (FertilityBlend) increases pregnancy rates in women who have trouble conceiving.
- Stomach cancer. There is inconsistent evidence about the effects of green tea on stomach cancer risk. One study suggests that drinking at least 5 cups of green tea daily does not reduce the risk of stomach cancer. Other research suggests that drinking at least 10 cups of green tea daily reduces the risk of stomach cancer.
- High blood pressure. There is inconsistent evidence about the effects of green tea on blood pressure. Some research shows that drinking green tea regularly can lower the risk of developing high blood pressure. However, other research shows that it has no effect on blood pressure in people with or without high blood pressure.
- Allergy to Japanese cedar (pollinosis). Early research suggests that drinking a green tea drink daily for 6 weeks before being exposed to Japanese cedar pollen can reduce allergy symptoms, including throat pain, nose blowing and tears.
- Leukemia. Population research suggests that Taiwanese people who drink higher amounts of green tea have a lower risk of developing leukemia.
- Lung cancer. There is inconsistent evidence about the effects of green tea on lung cancer risk. One study suggests that drinking at least 5 cups of green tea daily does not reduce the risk of death related to lung cancer. However, men who consume high amounts of phytoestrogens, chemicals found in green tea, have a lower risk of developing lung cancer.
- Metabolic syndrome. Early research suggests that taking 1000 mg of green tea extract daily or drinking four cups of green tea daily for 8 weeks does not improve blood pressure, cholesterol levels, or blood sugar in obese people with metabolic syndrome.
- Obesity. There is inconsistent evidence on the effects of green tea in obese people. Some early research shows that some specific green tea extracts (AR25, Exolise; Sunphenon) reduce weight in people with obesity. Other research suggests that drinking green tea can reduce body weight and body mass index (BMI) in overweight people. However some research suggests that taking green tea extracts or drinking green tea does not reduce body weight or BMI.
- Mouth cancer. Early research suggests that taking green tea extract three times daily after meals for 12 weeks increases healing responses in people with oral cancer.
- Gum disease (periodontal disease). Chewing candy that contains green tea extract seems to control plaque build-up on the teeth and reduce gum swelling. Also population research suggests that drinking green tea is linked with a reduced risk of gum disease.
- Pneumonia. Research suggests that Japanese women who drink green tea have a lower risk of death from pneumonia compared to those who don't drink green tea.
- Prostate cancer. Men who drink more green tea or who take products containing green tea antioxidants seem to have a lower risk of developing prostate cancer. However, green tea or green tea extracts do not seem to slow the progression of prostate cancer that has already been diagnosed.
- Stress. Early research suggests that taking a specific brand of green tea extract (Teavigo) by mouth for 7 days reduces stress and increases calmness.
- Stroke. According to one study in Japan, drinking 3 cups of green tea daily seems to lower the risk of having a stroke compared to drinking one cup or no tea.
- Upper respiratory tract infection. Early research suggests that gargling and swallowing green tea (Morgentau) over 4 days is less effective than citrus lozenges (Cystus052) for reducing symptoms of upper respiratory tract infections.
- Wrinkled skin. Some early research suggests that taking green tea antioxidants twice daily for 2 years does not reduce the signs of sun damage to the face in women. However, applying a green tea cream and taking green tea by mouth daily seems to improve some aspects of skin aging in women.
- Other conditions.
Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, and Insufficient Evidence to Rate (detailed description of each of the ratings).
Next: How does Green Tea work?
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