Talking about tea we have to distinguish between the different types:

- Black tea is the most common, with a strong aroma, originated from camellia plant that went
   through oxidation process.
- Green tea has more delicate flavor. It also comes from Camellia plant, but did not go
   through this oxidation process.
- Oolong is a combination of black and green tea.
- Herbal tea is a broad family based on plants, flowers and natural spices extracts which
   are also known as medicinal herbs due to their attributed healing properties.

As the medicinal qualities of tea are medically proven, its  popularity rises and consumption increases as well.
 

There's a Chinese saying that "Tea tempers the spirit, harmonizes the mind, dispels lassitude and relieves fatigue, awakens the thought and prevents drowsiness" but what else? Although it contains caffeine, a relatively negligible amount - only about a third than coffee, it is rich in body and soul positive healthy traits: it contains substances that reduce arterial calcification, Polyphenols that prevent the formation of tumors and has a high concentration of Flavanoids - a type of antioxidant.

 
A large-scale study published by the Journal of the American Medical Association, JAMA, in mid 2006 found that green tea reduces the mortality from heart disease.
 

Another extensive new study states that drinking both cold and hot teas on a regular basis reduces the risk of Parkinson's disease, thanks to the unique antioxidants natural components found in it. 
 

And what about green tea? A British study found that green tea's has the ability to delay the development of Alzheimer's disease through inhibition of the activity of an enzyme that plays a significant role in creating protein precipitation generated in the brains of Alzheimer patients. Moreover, Researchers from the Chinese University of Hong Kong have shown that drinking green tea can help prevent eye diseases.

 
Unlike black and green tea the doctors are divided in their opinions about the effectiveness and health value of many types of herbal tea as the multiple views on the effectiveness of the herbs themselves.

Since researches on the subject have not yet ended, it is still unclear what the antioxidants contribution is compared with other harmful ingredients. Therefore we should consume it moderately: no more than 3 green or black tea cups a day.
 

Also, a glass of black tea or green is not equal to a glass of water in the sense of human body need for fluids. On the contrary, the content of caffeine contributes to dehydration, therefore it is recommended to drink an extra glass of water for every cup of tea.

The same applies to herbal teas drinking especially if you drink only one kind. Each kind has its recommended dosage for its alleged contribution without damaging.

Well, enjoy the cup of your choice: black tea, green tea or herbal tea but don't overdo.