Should You Join the Tea Party?

[Warph]

Should You Join the Tea Party?
Legend has it that tea was discovered by a Chinese emperor nearly 5,000 years ago when the leaves of a nearby bush accidentally blew into his vat of boiling water. Over the centuries, as tea spread from the East to the West, it has become the most commonly consumed beverage in the world after water. In more recent years, scientists have uncovered an array of potential health benefits, from heart protection to anti-cancer and weight-loss effects. Should you drink a cup—or two or three—a day?

Steeped in wisdom
All tea comes from the Camellia sinensis shrub. ("Herbal teas" are made from other plants and are not true teas.) How the leaves are processed after harvest, however, determines what type of tea it will become. Green teas are minimally processed—the leaves are steamed, rolled, and dried—and are light in color and taste. Black teas are withered, rolled or crushed, and then "fermented" (in this case meaning oxidized, or exposed to oxygen) before being dried, which makes them black and stronger in taste. Oolong teas are partially fermented. White tea, a relative newcomer to the U.S., is harvested in early spring; the young leaves and silvery white buds are steamed and dried only.

Tea contains a range of polyphenols, notably flavonoids, which have antioxidant and other biological properties that are thought to help protect against disease. All teas have similar amounts of flavonoids, but the types and proportions depend on how they are processed. Green teas, for example, are rich in catechins, including the potent antioxidant EGCG; in black teas, the catechins convert into thearubigens and theaflavins during fermentation. Oolong teas fall in between in composition. Despite its almost clear color, white tea actually contains the most catechins. Various polyphenols may have different biological properties and thus different effects in the body, but at this point no one knows if any type is "best."

Other factors affect tea's polyphenols as well, including soil quality and growing conditions, the tea's age, how it's stored, and how it's brewed. Steeping tea at higher temperature for a longer time boosts polyphenols, while decaffeinating tea reduces catechins slightly. Lower levels of catechins have also been reported in instant and bottled teas. Though the studies are not consistent, adding milk may bind catechins and block some of tea's benefits.

Tea also contains caffeine, unless it has been decaffeinated. The amount depends on the type/blend, how much you use, how long you brew it, and whether it's loose or bagged. A 6-ounce cup generally has about 40 milligrams of caffeine—less than half that of coffee. Black tea tends to have more caffeine than green, but white tea may have more than green.

A cuppa benefits?
But can drinking tea actually improve your health? Studies have yielded complex and contradictory results. While green tea has gotten the most buzz, the FDA has denied proposed health claims on labels linking green tea with a reduced risk of various cancers or cardiovascular disease, saying that evidence is limited or lacking.

Here's a brief look at some of the research:

• Heart health. Population studies, including a recent one from Japan in the Journal of the American Medical Association, link tea consumption with a reduced risk of cardiovascular disease. Tea may lower LDL ("bad") cholesterol and make it less susceptible to artery-damaging oxidation, as well as improve blood vessel functioning, lessen inflammation, and inhibit blood clotting. But not all studies show heart benefits, and a Greek study found that black tea had an adverse stiffening effect on the aorta, the main artery that carries blood from the heart, while both black and green tea boosted a variable indicating increased load on the heart.

• Cancer. In lab and animal studies, tea polyphenols have been shown to inhibit a variety of cancers, including colon, bladder, pancreas, lung, skin, and prostate. However, results in human studies have been less consistent. Several observational studies in women from Europe, China, and the U.S. have linked tea with reduced risk of ovarian cancer, for example. On the other hand, a review article from the Washington University School of Medicine in St. Louis cited mixed results on tea and lung cancer, with some studies finding it protective, others showing no link, and still others suggesting that it may increase the risk.

• Body weight. There's some evidence that tea may have a weight-loss effect, though not all studies find this, and any effect would be modest at best. In a small study a few years ago, oolong and green tea boosted energy expenditure in healthy women. And in a review by Swiss researchers, most studies found that green tea or green tea extract reduced body weight and body fat. Tea polyphenols may stimulate energy metabolism and boost fat burning, but part of the effect may also be due to tea's caffeine.

• Bone health. Several studies, including a recent one from Australia looking at women age 70 to 85, have found that long-term tea drinkers tend to have greater bone density than nondrinkers. Tea contains fluoride, flavonoids, and other compounds that may be good for bones.

• The brain. Lab and animal studies support the role of tea in aiding cognition. Studies in people, however, are limited. In one study in 2006, older people in Japan who reported drinking as little as four to six cups of green tea a week had a reduced risk of cognitive impairment compared to those who drank less.

Bottoms up
Tea's effects in the body are still not fully understood, but don't expect it alone to prevent heart disease, cancer, or any other conditions. Moreover, it is just one source of polyphenols—many fruits and vegetables, red wine, and cocoa are others. Nevertheless, tea can be a healthy addition to your daily diet. And all types have something to offer. Without added sugars, tea has only two calories per cup. Check the labels on bottled and instant teas, however, since many have lots of calories from added sugar. If you don't like caffeine, buy or order decaffeinated tea.

Skip green tea supplements, which vary in composition, even between batches, and may not contain what the label says. There's no evidence that they have long-term benefits or are safe. And some, particularly those marketed for weight loss, may contain high doses of caffeine.

UC Berkeley Wellness Letter 2009