After water, tea is the most commonly consumed beverage in the world. This is good news, because tea offers important health benefits.

Green tea was the first tea studied for its cancer-fighting benefits. Recent research shows that any tea derived from the leaf of a warm-weather evergreen known as Camellia sinensis has similar cancer-fighting properties. This includes all green, black and red (oolong) teas. The leaves of this tree contain chemicals called polyphenols, which give tea its antioxidant properties. Herbal teas are not derived from this leaf and so do not have this particular health-promoting chemical.

The degree of processing determines whether a tea will be green, black or red. Green teas are the least processed. They are simply steamed quickly before packaging. Black and red teas are partially dried, crushed and fermented. The length of fermentation, which causes the leaves to blacken, determines whether the tea will be red or black. Regardless of the processing method, all teas contain polyphenols.

Polyphenols, like other antioxidants, help protect cells from the normal, but damaging, physiological process known as "oxidative stress." Although oxygen is vital to life, it's also incorporated into reactive substances called free radicals. These can damage the cells in our body and have been implicated in the slow chain reaction of damage leading to heart disease and cancer.

Many studies have demonstrated the anti-cancer properties of polyphenols. They can stop the damage that free radicals do to cells, neutralize enzymes essential for tumor growth, and deactivate cancer promoters. Their effect on heart disease is less well understood. Some laboratory studies have found that polyphenols help prevent blood clotting and lower cholesterol levels. The leap to preventing heart attacks, however, has not yet been made. The majority of evidence comes from studies done on lab animals. The effect on people is unclear.

Although much remains to be learned about the health benefits of tea, it is considered a good choice for at least some of the 6 to 8 cups or glasses of fluids recommended daily. The best teas are those brewed from loose leaves or tea bags of black, green or red tea, as they have the most antioxidant power. Allow your tea to steep for three to five minutes to allow the maximum amount of antioxidants to be released. Iced teas can provide as much antioxidant power as hot teas. Keep them covered and refrigerated. Bottled teas often have a lower antioxidant level because they contain mostly water and sugar.

Some people think that milk lowers tea's anti-oxidant power because it binds to polyphenols and inactivates them. This has not been proven, however, so go ahead and add some milk if you like. You'll also increase your calcium intake.

Tea also has fluoride for strong teeth, virtually no calories, and half the amount of caffeine found in an equally-sized cup of coffee. Whether decaffeinated teas have the same polyphenols, and thus the same health benefits, as regular teas has not yet been studied. Caffeine is a natural component of tea leaves. It is not yet known if removing caffeine also removes polyphenols.