When Americans drink tea, it's usually black tea, often iced (and in the South, sugared). Many of the recent studies on tea, however, have been done on green tea, served hot, the kind favored in Asia.
No one knows for sure whether tea type makes a difference when it comes to health, but experts say all kinds of teas from the Camellia sinensis plant probably have some health benefits. Each contains high levels of antioxidants, although the way tea is processed (for example, how long it's fermented before being packaged and shipped to stores) can change antioxidant levels as well as color and taste.
"If anything, the data would suggest that tea has benefits, and it doesn't much matter if it's green or oolong or black. But the real definitive studies haven't been done," says Jeffrey Blumberg, a tea researcher at Tufts Nutrition Center in Boston.
Green tea is made by picking the leaves and quickly heating them to stop oxidization, the process by which oxygen interacts with a substance to alter its chemical composition. Green tea typically has a mild, fresh taste.
Black tea is processed to fully oxidize and ferment the leaves and create a stronger taste. Some experts suggest that this could result in some variation in health benefits between black and green teas. Oolong tea is also oxidized, but less so than black teas.
The more rare white tea is considered the finest of teas because it consists of the youngest buds from the plant, which are still covered with whitish hairs when they're picked. White and green teas have the least amount of caffeine and appear to contain the highest levels of healthy polyphenols. But even black teas contain only about half as much caffeine as coffee.
As for temperature, there is no reason iced tea, which has been brewed first, wouldn't also carry health benefits, experts say. But the powdered, instant iced tea popular in this country contains only small amounts of tea. Researchers have little information on the health benefits of other tea variations, such as tea that is heavily flavored with milk and sugar or bottled teas that may contain other substances, such as sugar and preservatives.
Herbal teas are something entirely different. They're made from the leaves, flowers or roots of various plants, not the Camellia sinensis plant. Herbal teas can vary widely in terms of their health effects.