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Green, Black, and Red: The Tea-Total Evidence

Green tea is a likely choice these days for people looking for health benefits from their beverages. But new research indicates that all tea is good for you, as long as it comes from the leaf of Camellia sinenis—as do all green, black, and red teas. Herbal teas are another matter entirely: it's unlikely that any of them have the great combination of health-promoting chemicals contained in the plain old tea that people have been consuming for thousands of years.

Here's some background on tea. Once strictly an Asian crop, tea is now grown in mountainous areas of South America, Africa, and Turkey as well. But it's all the same plant. Whether it turns out to be black, oolong, or green depends on the processing. To make green tea, the leaves are steamed, rolled, and dried. This keeps them from oxidizing, because it inactivates certain chemicals in the leaves. Red (oolong) and black teas are partially dried, crushed, kept in a temperature- and humidity-controlled environment to produce fermentation, and then fully dried. To "ferment" in this context means "oxidize," or blacken; this takes place as chemicals in the leaves react to heat. The difference between black and red teas is that black teas are fermented longer. Hence the distinctive tastes and chemical properties of each kind of tea. Green is the favorite tea in Asia; black is preferred in Europe and the Americas.

The chemicals that make tea a potential protector of health are called polyphenols; these may have anti-cancer effects as well as heart benefits. Though green tea was once thought to have the most polyphenols, it turns out that black tea has a similar amount. The polyphenols in both green and black teas have antioxidant activity—that is, they help deactivate cell-damaging free radicals. Indeed, one study found that tea leaves have more antioxidant power by one measure than kale or strawberries, on a dry-weight basis (the study didn't compare common serving sizes). But don't conclude from this that you should give up fruits and vegetables in favor of tea. In fact, exactly what these tea antioxidants do in the human body is still to be determined.

Those powerful polyphenols

The polyphenols in tea seem to operate in a variety of ways: for example, halting the damage that free radicals do to cells, neutralizing enzymes essential for tumor growth, and deactivating cancer promoters. But most of this evidence comes from studies in the lab—in test tubes or on animals. Maybe the benefits occur in humans, maybe not. One study of 35,000 postmenopausal women found that consuming at least two cups of tea daily cut the risk of digestive and urinary tract cancers. Generally, though, studies of the effects of tea in humans have yielded contradictory results. It is possible that tea protects against cancer only in people who (a) drink huge amounts of it and (b) are at high risk for cancer because they have a poor diet.

The evidence that tea protects against heart disease is not as strong. In some lab studies, researchers have found that polyphenols help prevent blood clotting and lower cholesterol levels. And there's some evidence that tea drinking is associated with a reduced risk of heart attack. But it's too soon to recommend tea as a way to prevent heart attacks. There is also preliminary evidence that tea may help prevent arthritis. But, obviously, many tea drinkers do get arthritis.

Remember this: After water, tea is the most commonly consumed beverage in the world. Thus, while tea may have health benefits, it clearly is no panacea. Stomach cancer, for example, remains a major killer in China and Japan, where the highest amounts of green tea are consumed. But the evidence keeps mounting that tea has health benefits. Think of it as a back-up to a healthy diet and an adjunct to regular exercise and other good health habits—not as a miraculous potion that will keep you well by itself. If you smoke, for example, tea won't protect you from the dangers.