Green Tea Benefits
Since ancient times, green tea has been a staple of daily life in Asia, and known as a healing beverage. Green tea is made from unfermented leaves and reportedly contains the highest concentration of powerful antioxidants called polyphenols. Antioxidants are substances that scavenge free radicals -- damaging compounds in the body that alter cells, tamper with DNA (genetic material), and even cause cell death. Free radicals occur naturally in the body, but environmental toxins (including ultraviolet rays from the sun, radiation, cigarette smoke, and air pollution) also give rise to these damaging particles. Many scientists believe that free radicals contribute to the aging process as well as the development of a number of health problems, including cancer and heart disease. Antioxidants such as polyphenols in green tea can neutralize free radicals and may reduce or even help prevent some of the damage they cause.
Green tea has been consumed throughout the ages in India, China, Japan, and Thailand. In traditional Chinese and Indian medicine, practitioners used green tea as a stimulant, diuretic (to promote the excretion of urine), astringent (to control bleeding and help heal wounds), and to improve heart health. Other traditional uses of green tea include treating flatulence (gas), regulating body temperature and blood sugar, promoting digestion, and improving mental processes.
Green Tea and Alzheimer's
There is also growing evidence, backed by research studies around the world, that one of these protective compounds is effective in preventing the buildup of plaque in the brain, linked to Alzheimer's disease. This buildup of plaque, called beta-amyloid plaque, is widely believed by medical researchers to cause the nerve damage and memory loss of Alzheimer's disease.
Most of the flavonoids found in tea are "catechins", a basic form of flavonoid. Flavonoids are powerful antioxidants, and the catechins found in green tea contain among the highest flavonoid content of all plants. The primary catechin is called epigallocatechin-3-gallate, usually abbreviated to EGCG. EGCG is over 100 times as effective in neutralizing harmful free radicals as vitamin C.
Because oxidative damage and inflammation are significant contributors to neurodegenerative diseases such as Alzheimer's, the powerful antioxidant and anti-inflammatory effects of tea can be a valuable tool in Alzheimer's prevention. According to one expert, Dr. Bradford L. Frank, a medical school professor, "There is now a large body of scientific evidence demonstrating that certain natural compounds, such as catechins, improve age-related cognitive decline, and are neuroprotective for Alzheimer's and other brain diseases. This scientific evidence supports the beneficial effects of green tea on cognitive function and it's uses as a natural neuroprotective substance."
EGCG seems to change potentially harmful proteins into proteins that are not detrimental to brain cells, actually converting a toxic structure into a less toxic structure. Because EGCG binds to unfolded proteins -- which are not associated with Alzheimer's -- the green tea can be considered as medication that recognizes the more troublesome proteins and converts them to harmless substances.
Dosage
Depending on the brand, 2 - 3 cups of green tea per day (for a total of 240 - 320 mg polyphenols) or 100 - 750 mg per day of standardized green tea extract is recommended. Caffeine-free products are available and recommended.
Precautions
The use of herbs is a time-honored approach to strengthening the body and treating disease. However, herbs contain active substances that can trigger side effects and interact with other herbs, supplements, or medications. For these reasons, people should take herbs with care, under the supervision of a practitioner knowledgeable in the field of botanical medicine.
People with heart problems, kidney disorders, stomach ulcers, and psychological disorders (particularly anxiety) should not take green tea. Pregnant and breastfeeding women should also avoid green tea.
People who drink excessive amounts of caffeine (including caffeine from green tea) for prolonged periods of time may experience irritability, insomnia, heart palpitations, and dizziness. Caffeine overdose can cause nausea, vomiting, diarrhea, headaches, and loss of appetite. If you are drinking a lot of tea and start to vomit or have abdominal spasms, you may have caffeine poisoning. If your symptoms are severe, lower your caffeine intake and see your health care provider.
Possible Interactions
If you are being treated with any of the following medications, you should not drink green tea or take green tea extract without first talking to your health care provider:
Adenosine -- Green tea may inhibit the actions of adenosine, a medication given in the hospital for an irregular (and usually unstable) heart rhythm.
Antibiotics, Beta-lactam -- Green tea may increase the effectiveness of beta-lactam antibiotics by reducing bacterial resistance to treatment.
Benzodiazepines -- Caffeine (including caffeine from green tea) has been shown to reduce the sedative effects of benzodiazepines (medications commonly used to treat anxiety, such as diazepam and lorazepam).
Beta-blockers, Propranolol, and Metoprolol -- Caffeine (including caffeine from green tea) may increase blood pressure in people taking propranolol and metoprolol (medications used to treat high blood pressure and heart disease).
Blood Thinning Medications (Including Aspirin) -- People who take warfarin, a blood thinning medication, should not drink green tea. Since green tea contains vitamin K, it can make warfarin ineffective. Meanwhile, you should not mix green tea and aspirin because they both prevent platelets from clotting. Using the two together may increase your risk of bleeding.
Chemotherapy -- The combination of green tea and chemotherapy medications, specifically doxorubicin and tamoxifen, increased the effectiveness of these medications in laboratory tests. However, these results have not yet been demonstrated in studies on people. On the other hand, there have been reports of both green and black tea extracts stimulating a gene in prostate cancer cells that may cause them to be less sensitive to chemotherapy drugs. Given this potential interaction, people should not drink black and green tea (as well as extracts of these teas) while receiving chemotherapy for prostate cancer in particular.
Clozapine -- The antipsychotic effects of the medication clozapine may be reduced if taken fewer than 40 minutes after drinking green tea.
Ephedrine -- When taken together with ephedrine, green tea may cause agitation, tremors, insomnia, and weight loss.
Lithium -- Green tea has been shown to reduce blood levels of lithium (a medication used to treat manic/depression).
Monoamine Oxidase Inhibitors (MAOIs) -- Green tea may cause a severe increase in blood pressure (called a "hypertensive crisis") when taken together with MAOIs, which are used to treat depression. Examples of MAOIs include phenelzine and tranylcypromine.
Oral Contraceptives -- Oral contraceptives can prolong the amount of time caffeine stays in the body and may increase its stimulating effects.
Phenylpropanolamine -- A combination of caffeine (including caffeine from green tea) and phenylpropanolamine (an ingredient used in many over-the-counter and prescription cough and cold medications and weight loss products) can cause mania and a severe increase in blood pressure. The FDA issued a public health advisory in November 2000 to warn people of the risk of bleeding in the brain from use of this medication and has strongly urged all manufacturers of this drug to remove it from the market.
Useful Tips
- Allow tea to steep for three to five minutes to bring out its catechins.
- The best way to get the catechins and other flavonoids in tea is to drink it freshly brewed. Decaffeinated, bottled ready-to-drink tea preparations, and instant teas have less of these compounds.
- Tea can impede the absorption of iron from fruits and vegetables. Adding lemon or milk or drinking tea between meals will counteract this problem.
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