Historical evidence suggests that tea leaves boiled in water were consumed as far back as 5,000 years ago in India and China. These two countries were the earliest users of tea. Tea also plays a very important part in social rituals of Japan. In Asian countries tea has long played an important cultural role.

Tea is derived from leaves of a plant called Camellia sinensis. The plant is grown in Asia, the Middle East and Africa.

There are three types of tea - Green, black and oolong. All of these are derived from Camellia sinensis, the difference lying in the way the leaves are processed. Green tea is prepared from leaves that are not fermented; oolong tea is prepared from partially fermented leaves, while black tea leaves are fully fermented. Green and oolong tea are mostly consumed in Asian countries like China, Japan, India and Thailand, while black tea is preferred in United States.

In recent periods green tea has attracted a lost of attention due to many health benefits attributed to it. Many studies have been conducted which explore the link between consumption of green tea and incidence of certain diseases in the population. It has been observed that green tea is helpful in:

- preventing cancer,

- improving the ratio of 'good' (HDL) cholesterol to 'bad' cholesterol,

- cognition,

- treating flatulence,

- regulating blood sugar,

- regulating body temperature,

- improving digestion.

In some studies it was suggested that the lower incidence of heart related diseases in the French population in spite of the consumption of a fat rich diet is related to the drinking of large quantities of green tea by them. This may be compared to the lower incidence of heart diseases in Japanese population, 75% of which are heavy smokers.

The medicinal properties of green tea are attributed to the presence of polyphenols, which act as antioxidants. Antioxidants help prevent the damage caused by free radicals present in body. Free radicals occur naturally, but they grow in numbers due to some environmental conditions like pollution, ultra-violet light, cigarette smoke etc. Green tea contains 30% to 40% polyphenols, while black tea contains up to 10% polyphenols.

3 to 4 cups of green tea is recommended for an adult.

Green tea has been found to be beneficial in following conditions :

(1) People who drink green tea are found to have lower LDL cholesterol levels and higher HDL cholesterol levels. One study conducted in animals suggests that polyphenols may help inhibit the absorption of cholesterol by intestines thus helping in the excretion of cholesterol from body.

(2) Though it has not yet been conclusively proved that drinking of green tea is related to the lower incidence of caner in Japan, yet some studies conducted in animals indicate that polyphenols that act as antioxidants may be responsible for killing the cancer cells.

(3) It was found in certain studies that polyphenols help control Type 1 diabetes. The body stops producing insulin in Type 1 diabetes. Green tea can be helpful in regulating levels of glucose in the blood in such cases.

(4) Green tea has also been found to be beneficial for the liver. It helps control the damaging effect of alcohol on it. People who drink green tea are found to have lower incidence of liver diseases.

(5) Green tea may also be helpful in reducing weight in obese people. Though not conclusively proved, weight reducing properties of polyphenols have been noted in some studies.

In some cases, however, certain precautions need to be taken while taking green tea.

People with stomach ulcers, heart problems, hyperthyroidism and psychological disorders should not take green tea. Pregnant women should also avoid it. Green tea should also be avoided if one is taking any of the following medications: anti-biotics, Benzodiazepines, Beta blockers, blood thinning medicines, chemotherapy, oral contraceptives and lithium.