People have been drinking green tea for thousands of years, with its use in China recorded as early as 5,000 years ago. Made from the dried leaves of an evergreen shrub called Camellia sinensis, green tea has been used for a variety of health purposes, such as improving mental alertness, weight loss and treating stomach disorders. It contains very high concentrations of antioxidants and as such has been studied extensively for its effects on various diseases.
Green Tea and Antioxidants
Green tea contains large amounts of antioxidants called catechins. These substances counteract free radicals, which are compounds that damage DNA and lead to cell death, cancer, atherosclerosis and blood clot formation. They are also believed to influence the aging process. Green tea is able to maintain high concentrations of antioxidants because it is only minimally processed. Unlike other teas, which are fermented, green tea is only withered and steamed before drinking.
Cancer
Many clinical studies show the positive effects of green and black teas on cancer prevention, the University of Maryland Medical Center reports. These population-based studies linked regular consumption of green tea with lower rates of cancer incidence, as illustrated by countries such as Japan. However, whether it is green tea that is actually responsible for cancer prevention is still undecided. Other, more specific clinical studies done on smaller groups of patients have shown a positive correlation between regular green tea use and lower rates of diseases such as pancreatic, breast, bladder and prostate cancers. Researchers believe that polyphenols in green tea help eliminate cancerous cells and prevent their spread.
High Cholesterol
Green tea has been shown to simultaneously lower total cholesterol while increasing HDL, or good, cholesterol in patients, explains MedlinePlus, a service of the National Institutes of Health. Men who drank green tea were more likely to have lower overall cholesterol than those who did not drink it. Researchers think that the polyphenols in green tea help the body flush out excess cholesterol and block its absorption in the intestines. Male smokers who drank green tea in another study were also found to have greatly reduced levels of LDL, or bad, cholesterol.
Liver Disease
Green tea has been associated with lower incidence of kidney disease, as the University of Maryland Medical Center explains. It also may protect the liver from the damage sustained from excessive consumption of toxic substances such as alcohol. Animal studies in mice have shown green tea's protective quality against the formation of liver tumors. In addition, several studies on both humans and animals show that the catechin polyphenols in green tea may help alleviate viral hepatitis, where the liver is inflamed from a viral infection.
Safety Concerns and Side Effects
Green tea is considered safe for consumption for most adults, the National Center for Complementary and Alternative Medicine reports. However, too much green tea -- over five cups per day -- may cause negative side effects due to the tea's caffeine content. High doses and chronic use may result in psychological dependence and tolerance. Sudden discontinuation of use may lead to withdrawal symptoms. In addition, patients with severe liver disease should use caffeine with caution.
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