Heath Benefits of Black Tea, Green Tea, Oolong Tea and White Tea.

	Green Tea Health Benefits and Applications
	Is Tea Good for Your Health?

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Summary: Health Benefits of Tea

The legend is that tea was discovered by the Chinese Emperor Shen Nung around 2,737 B.C. The emperor drank a potient made of boiling water and tea leaves. All tea is made from the Camellia sinensis plant. The Camellia sinensis plant is the source of all nonherbal teas.

Tea comes in black, green, oolong and rare white varieties, all produced from the leaves of Camellia sinensis, a white-flowered evergreen. Any other type of herbal tea must be labeled with the name of the plant the product is made from.

Since 2,737 B.C. tea drinking has been regarded as an aid to good health and invigoration. Researchers are now studying tea for possible use in the prevention and treatment of a variety of cancers, cholesterol control, weight loss and for its ability to increase insulin activity.

Antioxidants, Cancer and Tea

The human body constantly produces unstable molecules called oxidants or what is commonly referred to as "free radicals". Oxidants take electrons from otherwise healty cell molecules and in the process damage cells and genetic material. This damage may leave the cell vulnerable to cancer.

Antioxidants are substances that allow the human body to hunt down and seize oxidants making them harmless. Tea contains an antioxidant called catechins. These catechins found in tea selectively inhibit specific enzyme activities that lead to cancer. They may also target and repair DNA aberrations caused by oxidants.

Green, oolong and black tea all contain catechins. Studies indicate that steeping tea for about five minutes will release over 80 percent of its catechins. Instant iced tea has been shown to contain negligible amounts of catechins.

Laboratory studies have shown tea catechins act as powerful inhibitors of cancer growth in several ways: They scavenge oxidants before cell injuries occur, reduce the incidence and size of chemically induced tumors, and inhibit the growth of tumor cells.

Tea Consumption Lowers Blood Cholesterol

Drinking tea lowered low-density lipoprotein, the LDL "bad" cholesterol, in a small group of volunteers in an Agricultural Research Service study reported in the October, 2003 issue of the Journal of Nutrition.

"These findings illustrate the impact of specific types of health-promoting phytonutrients on the diet," said Ed Knipling, Acting Administrator for ARS. Judd's study assessed the effects of black tea consumption on blood lipid concentrations in adults with mildly high cholesterol.

"Overall, we found a 6 to 10 percent reduction in blood lipids in black tea drinkers in just three weeks," said Judd. The study showed no effect on high-density lipoprotein, the HDL "good" cholesterol. The study's authors concluded that drinking black tea, in combination with following a prudent diet moderately low in fat, cholesterol and saturated fatty acids, reduces total and LDL cholesterol by significant amounts and may reduce the risk of coronary heart disease.

Tea and Weight Control

Physiologist William Rumpler is investigating the ancient Chinese belief that tea is effective in controlling body weight. Rumpler is with the ARS' Diet and Human Performance Laboratory, one of seven laboratories that make up the Beltsville Human Nutrition Research Center (BHNRC) in Beltsville, Maryland.

"Our data suggested that a component of tea other than caffeine might have promoted preferential use of fat as an energy source," says Beverly Clevidence.

The results showed that the energy expenditure of volunteers was about 3 percent higher after they drank either the caffeinated water or the full-strength tea than after they drank the colored water. On average, the volunteers burned an additional 67 calories a day when they drank tea instead of an equal amount of water. Perhaps most interesting was that fat oxidation was a significant 12 percent higher after the full-strength tea treatment than after the water treatment.

It is universally accepted that caffeinated tea raises metabolic rate because caffeine is a stimulant. "The interesting part of our study, which agreed with findings from a similar study in England, was that when you drink tea you turn on the fat-burning spigot a little bit more than when you drink caffeinated water," says Rumpler. Some scientists speculate that caffeine combined with highly active catechin found in tea may act together to increase fat oxidation.

Tea Found to Enhance Insulin Activity

ARS chemist Richard Anderson found that regularly brewed tea, when added to the fat cells of laboratory rats, increased insulin activity by more than 15 times. Anderson is with the BHNRC's Nutrient Requirements and Functions Laboratory. He noted that this increased insulin activity was found with green, black, and oolong teas, regardless of whether caffeinated or decaffeinated.

Ernst J. Schaefer, director of the HNRCA's Lipid Metabolism Laboratory, completed a pilot study in 2003 during which 8 volunteers with type II diabetes had lower blood sugar levels by 15 to 20 percent after drinking 6 cups of tea per day for 8 weeks. Schaefer and Blumberg have since launched a 24-week, randomized, double-blind study involving 40 male and female volunteers with type II diabetes, not taking insulin. "We want to examine the effect that green and black teas have on the glucose levels of the volunteers," says Schaefer.

Although further confirmational studies on tea and insulin activity in relation to people are needed. Blumberg says consuming a variety of tea types and preparations adds nutritional benefits to the diet. "The beauty of tea is that it can be enjoyed in so many ways, depending on individual tastes and preferences," he says. "My hope is that future studies will be designed to accurately assess tea's polyphenol levels and to measure tea's role in lowering the risk of chronic diseases."

Antibacterial effects

Tea extracts exhibit inhibitory effects against Salmonella typhi, Campilobacter jejuni, Campilobacter coli, Helicobacter pylori, Shigella, Clostridium, Pseudomonas, Candida and others.

Dental Caries

Green tea and various catechins have exhibited inhibitory effects on the growth of cariogenic bacteria by preventing the adherence and growth of bacteria at the tooth surface.