Black tea is made from the leaves of a bush called Camellia sinensis. A process called oxidation turns the leaves from green to a dark brownish-black color. Oxidation means the leaves are exposed to moist, oxygen-rich air.
Tea manufacturers can control the amount of oxidation. Black tea is a fully oxidized tea. Green tea comes from the same plant, but is not oxidized.
Many people drink black tea for alertness and energy. There is good scientific evidence to show this works. Black tea has a lot of caffeine. It also contains a little bit of a stimulating substance called theophylline. Both can speed up your heart rate and make you feel more alert.
Black tea is also full of healthy substances called polyphenols. Polyphenols are antioxidants that can help protect your cells from DNA damage.
Some scientists think that specific antioxidants in tea, including polyphenols and catechins, may help prevent some types of cancer. For example, some research shows that women who regularly drink black tea have a much lower risk of ovarian cancer than women who do not.
But larger-scale studies are needed to confirm these uses.
Black tea extract is sold as a supplement. Sometimes, the supplement includes other types of herbs, vitamins, or minerals.
Drinking a moderate amount of black tea (one to four cups a day) may boost blood pressure slightly, but the effect does not last long. And drinking this amount of black tea is not associated with long-term high blood pressure.
Preliminary studies in people show that a black tea supplement can boost metabolism and increase blood pressure. Changes in blood pressure can be a concern. However, a small increase may be helpful for people who have dizziness due to low blood pressure when they stand up.
Optimal doses of black tea have not been established. Supplement ingredients and quality may vary widely. This makes it hard to set a standard dose.