Next to water, tea is the most widely consumed drink in the world. In particular, green tea is receiving a lot of attention from medical experts due to its perceived health benefits. It has been used for thousands of years in China and India, and today it is consumed either as an infusion or as an extract made from the tea leaves. Green tea has been associated with a reduction in the incidence of diseases such as cancer, diabetes and liver disease, though it also has some contraindications.
Cancer
The most highly-touted benefit of green tea is its positive effect against cancer. Clinical studies have shown that there is indeed a link between regular green tea consumption and a reduction in certain types of cancer, the University of Maryland Medical Center reports. These include breast cancer, bladder cancer, pancreatic cancer, skin cancer, prostate cancer and ovarian cancer. Scientific studies suggest that the high antioxidant content and polyphenols in green tea help stave off the onset of cancer in general.
Diabetes
Laboratory research seems to indicate that polyphenol antioxidants found in green tea may support healthy insulin activity and regulate blood sugar in the body. Animal studies suggest a reduction in the risk of type 1 diabetes and slowed progression of the disease once it develops. However, according to the National Center for Complementary and Alternative Medicine, this is not yet conclusive. Nonetheless, some clinical studies concerning Japanese women who drank green tea have found a greatly reduced risk of developing type 2 diabetes.
Liver Disease
Green tea may protect against liver damage and lower the risk of liver disorders, the University of Maryland Medical Center says. Clinical studies on men who drank more than ten cups a day showed they were less likely to develop liver disease, while studies on mice showed a reduced incidence of tumors. The catechin content in green tea may also help treat viral hepatitis, thereby successfully reducing inflammation. Note that the catechin was isolated from green tea and used in high concentrations and was not obtained from drinking a green tea beverage.
Negative Side Effects
Although green tea is considered safe for most adults, drinking too much of it is inadvisable, as MedlinePlus, a service of the National Institutes of Health, reports. This is because it contains caffeine -- like any other tea. Consuming more than five cups of green tea daily may lead to negative effects such as vomiting, headache, diarrhea, irritability, difficulty sleeping, dizziness, confusion, heartbeat irregularities, tremors and heartburn. Toxicity can occur as a result of excessive consumption and reaching a caffeine dosage of 10 to 14g may actually be fatal.
Special Precautions
Pregnant and breastfeeding mothers should not drink more than two cups of green tea per day so as to limit the amount of caffeine they consume. Drinking more than this amount is associated with a heightened risk of miscarriage and other pregnancy complications. The caffeine may also be passed onto the baby through breast milk.
Furthermore, caffeine in green tea may also worsen existing cases of anxiety and anemia, temporarily worsen glaucoma, and increase the risk of bleeding, the National Center for Complementary and Alternative Medicine says. Green tea extracts have been associated with liver disorders, though this does not extend to green tea beverages themselves.
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