Black Tea is made from the dried leaves of Camellia sinensis, a perennial evergreen shrub. It has a long history of use. Black Tea, Green Tea, and Oolong Tea are all derived from the same plant. Black Tea is one of the most common teas known to mankind. It has been used throughout history for medical purposes, long before it became a breakfast tea. Black Tea is a source of caffeine, a methylxanthine which stimulates the central nervous system, relaxes smooth muscle in the airways to the lungs, stimulates the heart, and acts on the kidney as a diuretic. It also contains polyphenols (catechins, anthocyanins, phenolic acids), tannin, trace elements, and vitamins. Unlike high levels of caffeine found in coffee, the low amounts in Black Tea promotes blood flow in the brain without overstimulating the heart. The caffeine in Black Tea sharpens mental focus and concentration, and the trace element fluoride inhibits tooth decay. Black Tea also contains abuindant tannins, astringent chemicals and soothing anti-inflammatory effects on the digestive tract.
Some of the studies have revealed that Black Tea is found to help cut levels of the stress hormone cortisol circulating in the blood. It soothes away stress. In addition, researchers also found that blood platelet activation was lower among Black Tea drinkers. It also helps relieve diarrhea, lowers cholesterol levels and helps prevent tooth decay. It has a therapeutic effect on gastric and intestinal illnesses because of its tannins, which decrease intestinal activity and exerts an antidiarrheal effect. In addition to improving circulation, the theophylline in Black Tea helps improve cholesterol levels. Drinking two cups of Black Tea for three weeks every day and it shall open the blood flow in the capillaries and helps maintain normal blood pressure. It also has been known to expand the airways, making breathing easier for astmatics. Fluoride, a trace element found in Black Tea, strengthens tooth enamel, thereby helping to prevent tooth decay.
Medline Plus. http://www.nlm.nih.gov/medlineplus/druginfo/natural/patient-black_tea.html
BBC News. http://news.bbc.co.uk/1/hi/health/5405686.stm