All varieties of tea - green, brown or black are derived from the leaves of the same evergreen tree or bush, named Camellia sinensis. The first description of tea drinking is found in the ancient Chinese literature dating back to 350 AD.

The leaves of the plant are pricked, pressed and roasted and boiled in water with ginger and orange to make a herbal soup. It was bitter and considered to be a remedy for stomach problems and poor eyesight. In China the ritual of drinking tea was symbolic of harmony among men.

The Japanese were the first to claim that green tea  enhances health, reduces blood cholesterol, prevents cancer, and reverses ageing.

Tea contains caffeine, vitamin C, B and E, flavonoids, and polysaccharides which lower blood sugar, and fluorides that prevent dental cavities. 
 
Black and Green Teas

Both black and green teas come from the same plant named Camellia sinensis. Different processes are employed to make both the types of tea. The leaves for black tea are fully oxidized, and for green tea are steamed before being dried. Black tea mostly comes from Africa, India, Sri Lanka, and Indonesia. While green tea comes from China and Japan.

Composition of Tea

Both teas contain flavonoids which differ in their chemical structure. Green tea contains more of Catechins, while the oxidation undergone by black tea converts these simple flavonoids to more complex varieties called theaflavins and theaarubigins.

Caffeine content of Tea

Caffeine is found in Coffee beans (Coffea arabica), in the leaves of Thea sinensis, in the beans of cocoa, and in Kola nut. The three xanthines - caffeine, theophylline, and theobromine - are closely related plant alkaloids, and are CNS stimulants in decreasing order of potency.

Caffeine produces an increased capacity for sustained intellectual work, shortened reaction time, perfect association of ideas, and better memory.

In addition, the methylxanthines stimulate the heart, relax smooth muscle, improve skeletal muscle work, and have a diuretic effect.

Caffeine concentration in commonly consumed beverages:

Health benefits of Flavonoids

The oxidative process modifies the type of flavonoids, and their antioxidant activity is similar in both black and green tea.

A Japanese study has shown that regular consumption of green tea (more than 3 cups a day) may be protective against breast cancer in early stages. Thus green tea is anti carcinogenic, antioxidant, antiinflammatory, anti-rheumatic, cholesterol lowering, antibacterial, and antiviral.

The polyphenols have a protective action against ultraviolet radiation induced skin problems. Green tea also helps in weight reduction by speeding up the oxidation of fats.

Thus, the health benefits of both black and green tea are comparable in promoting health and well being. Consumption of tea also helps in fluid replacement in the body. A variety of teas are available today with special documented benefits.

Reference: Book Lifestyle and Health by Dr. H.K. Chopra, A Sterling Paperback, 2006