I found a  professional article that talks about ingredient composition of black tea. This is a persuasive angle to show benefits from tea drinker. 

Souce: By Susan Elliott–http://www.ehow.com/about_5399069_health-effects-tea.html

A tea is either made by infusion or decoction. The typical way to make a tea is by infusing herbs with water. An infusion is made by using the soft leaf or flower parts of the plant. Decoction is the process of making tea from the hard parts of a plant. Decoction requires a much longer boiling and steeping process than a tea infusion. However, no matter which process is used to make a tea, the many health benefits of tea can still be enjoyed.

Flavonoids

  • Black tea contains flavonoids. According to Dr. Gaby, coauthor of “The Natural Pharmacy,” flavonoids “support health by strengthening capillaries and other connective tissue, and some function as anti-inflammatory, antihistaminic and antiviral agents.”

    Tannic Acid

  • Black tea also contains tannic acid. Tannic acid has both antibacterial and astringent agents. Tannic acid can have a good effect on toothaches, ulcers and wounds. Some dentists tell patients to place cool tea bags on the area of the mouth where a tooth has been pulled to help decrease the chance of infection.

    Curative properties

  • The-color-of-tea.com provides studies done by researcher Milton Schiffenbauer of Pace University that show the many benefits of black tea. Schiffenbauer concluded that black tea helps to destroy many viruses that are found in the mouth. It can prevent and shorten the length of diarrhea, pneumonia, cystitis and skin infections.

    Preventative properties

  • There are also several preventative benefits from drinking black tea. These include the possible prevention of prostate cancer, breast cancer and stomach cancer. This is mainly due to the fact that the compound TF-2 is found in tea. TF-2 has been shown to deter the growth of cancerous cells. Black tea may also prevent tooth decay, relieve arthritis, and help burn excess fat.