Tea, is the second most consumed beverages in the world after water and well ahead of coffee, beer, wine and carbonated soft drinks. It is made up from leaf and bud of the plantCamellia sinensis. “Originating from China, tea has gained the world’s taste in the past 2000 years. In literature Tea classic” by Lu Yu it has been reported that SHUNG dynasty of china first uses green tea as medicine. After them Mangols started using it as health drink. While in India after the estabilishments of East India Company, Britishers started the trade of green tea from Asia and Europe. Darjeeling is famous for tea cultivation in India.It is consumed in different part of the world green, black or oolong tea. It has been estimated that worldwide production of tea is about 2.5 million tons and mainly consumed inAsia, some parts of North Africa, the United States, and Europe. It has been already proved by scientist around the globe the association between tea consumption especially green tea and human health.

Classification of tea:

Based on differences in manufacturing processes, teas are classified into three major types

1. Green tea: They are non-fermented variety of tea, to produce green tea freshly harvested leaf are steamed to prevent fermentation yielding a dry stable product.
2. Oolong tea: Semifermented variety of tea produced by partial fermentation of fresh leaves before drying.
3. Black tea: Tea leaf undergo post-harvest fermentation before drying and steaming.

Composition of green tea:

Howeverpotential health benefit of green tea is ascribed to the composition of green tea has been explored in last two decades. The composition of green tea is complex constitute mainly  proteins, amino acids such as theanine or 5-N-ethylglutamine, glutamic acid, tryptophan, glycine, serine, aspartic acid, tyrosine, valine, leucine, threonine, arginine, and lysine; carbohydrates such as cellulose, pectins, glucose, fructose, and sucrose; minerals and trace elements such as calcium, magnesium, chromium, manganese, iron, copper, zinc, molybdenum, selenium, sodium, phosphorus, cobalt, strontium, nickel, potassium, fluorine, and aluminum; and trace amounts of lipids (linoleic and α-linolenic acids), sterols (stigmasterol), vitamins (B, C, E), xanthic bases (caffeine, theophylline), pigments (chlorophyll, carotenoids), given in table 1,

Table 1: comparison of composition (% of dry weight) in green tea and black tea,

Figure-1: Principal differences between green and black tea processing and its influence on the final polyphenols content.

Green tea contains polyphenols and the major class of polyphenols and due to these compounds green tea are considered as energy drinks the class of polyphenols are phenolics and flavonoids i.e. catechins, theophylline, theanine, caffeine, kaempferoletc. structures are given in figure 2.

                        Figure 2. Common polyphenols found in green tea

Green tea and human health:

Since ancient time it has been shown that consumption of green tea prevent many types of disease. Health promoting effect of green tea is mainly because of the polyphenolic compounds presents in it the common health benefit of green tea are given below,

• Scientific studies shows that green tea has potential to improve blood flow, decreases blood cholesterol level.
• The components (polyphenols, α-reductase, Vitamin E) presents in green tea are good for hair health and development and prevents hair fall.
• Constituents of green tea reported to have antioxidant property which eliminates toxic compounds presents inside body and good for healthy skin.
• Many studies reported that green tea prevent a range of cardiac issues from optimizing blood pressure to decreasing the risk of congestive heart failure.
• Green tea contains numerous components with antioxidant activity such as polyphenols (catechins), minerals vitamins. Because catechins seems to control blood pressure and blood glucose so they are good for diabetic patients.
• Catechins have strong antioxidative property and it has been widely accepted through in vitro and in vivo studies that it possess antimutagenic, antidiabetic, anti-inflammatory, antibacterial and antiviral properties.
• Recent human studies suggest that green tea may contribute to reduce the risk of cardiovascular disease and cancer, and has anotherbeneficial effect on health.
• Caffeine, xanthine bases present in green tea acts mainly upon the central nervous system responsible for stimulating wakefulness, and decreasing fatigue and for healthy memory.
• Theophylline responsible for the increased psychoactive activity it also has vasodilator and diuretic property.
• In Chinese medicine green tea shows to have hypotensive activity.
• Some researchers shows the potential role of green tea in weight control.

Side effects of green tea: 

High use of green tea can be harmful to the health,

• Pregnant ladies should avoid higher consumption of green tea because caffeine presents in green tea may cause miscarriage or some defects in developing embryo.
• Hyper consumption of green tea may cause anaemia
• Higher dose of green tea increases the concentration of calcium in blood, which is harmful for the body and bone health.

Conclusion:

Since the beneficial effect of green tea to human health are being increasingly proved and taking all this into account it is advisable to go for a tea break and grab you next cup of tea.