Oolong tea is made from leaves of the same plant that green and black teas come from. The difference lies in how long the leaves ferment. Green tea leaves are unfermented, while leaves for black tea are fully fermented. Oolong comes from leaves that are partially fermented.
Fermentation, or its lack, gives teas their color and aroma. It also alters tea's chemical makeup. The most notable changes happen in a group of chemicals called catechins. These are strong antioxidants that may act directly on human cells.
Phenylalanine comes in several forms as a supplement:
L-phenylalanine is an essential amino acid. It's also found in protein in the foods we eat.
DL-phenylalanine, which contains both the D- and L-forms
Tea is a caffeinated beverage. A major benefit of drinking oolong tea is heightened awareness and energy along with sharpened thinking skills.
These effects are directly related to the level of caffeine, and a related chemical, theophylline. The effects increase as the caffeine level increases.
Some drink oolong tea to prevent or treat obesity and diabetes. One study suggests that drinking six cups of oolong tea daily for 30 days might help people with type 2 diabetes reduce blood sugar. Other studies -- in both humans and animals -- suggest that drinking oolong tea can help in weight loss.
Some people drink oolong tea because of a belief that it helps with other conditions, such as:
But studies done in these areas have been inconsistent and not conclusive.
Some studies have suggested tea might offer some protection against mental decline. While a recent study in China supported the idea that oolong tea might offer that protection, the results weren't conclusive and further study is needed.
Researchers have been interested in the potential of tea -- especially green tea -- to help treat or prevent some cancers. Studies done on animals have been encouraging. The evidence from human studies is still mostly inconclusive. But some evidence suggests that women who drink two cups of tea daily -- green, oolong, or black -- can significantly lower their risk of ovarian cancer.
What are the risks of oolong tea?
The major risks of oolong tea are the risks associated with drinking caffeine chronically or excessively. They include: