Fit To A Tea

Scientists are trying to discover whether the ancient beverage is good for the mind and the body

October 11, 2007|By Dennis O'Brien | Dennis O'Brien,Sun reporter

Six times this past summer, Richard Thomas spent 24 hours in a hermetically sealed room about the size of a jail cell - as a human lab rat at a federal research facility in Beltsville.

He could surf the Internet, watch television and make phone calls. But every morsel he ate was carefully measured. Every iota of gas he exhaled was closely monitored. And, occasionally, he had to extend his arm through a tube so scientists could draw blood.

"I didn't really fear it, but I don't fear going to the dentist either. It was a little like that," said Thomas, 54, of Columbia, who volunteered for a study to determine whether drinking tea is good for you.

The effort, by the Agricultural Research Service, is one of a several studies nationwide investigating whether this ancient and popular beverage provides benefits that range from improving concentration to reducing cancer risks.

"It's not settled, but there's increasing evidence there are protective trends with regard to tea," said David Ringer, scientific program director for the American Cancer Society.

In New York, researcher John Foxe says brain scans of a dozen volunteers show that an amino acid found in tea - known as theanine - activates neural regions that enhance our ability to focus.

"There's something about tea that makes us feel good. It helps us to pay attention," the neurophysiologist at the City College of the City University of New York told colleagues at a conference on the health benefits of tea last month in Washington. His work was financed by Unilever, maker of Lipton tea.

At the same meeting, Dr. Iman Hakin, dean of the college of public health at the University of Arizona, reported plans to use $9 million in Department of Defense funding to investigate whether compounds in green and black tea protect smokers and former smokers from cancer.

In small studies on diabetics, researchers also have found that EGCG, a compound common in green tea, decreases insulin resistance and improves insulin's effects on blood flow in diabetics.

The health benefits of tea are often linked to the blend of catechins, polyphenols and other antioxidants believed to protect the body from the kinds of cell damage that make us more vulnerable to cancer, scientists say.

But experts caution that most research has been limited to studies involving small numbers of human volunteers and to conclusions based on the effects of tea compounds ingested by lab rats and mice. "The evidence does not give clear proof with regard to humans and more research is needed," Ringer said.

Part of the problem is the complexity of the brew itself.

All four types of nonherbal tea - green, white, oolong and black - come from leaves of the same Camellia sinensis plant. But they're produced in different ways and contain different compounds that are likely to have different health effects, said Beverly Clevidence, an ARS researcher.

To make green tea, the leaves are heated or steamed soon after harvesting.

To turn tea from green to black - the most popular tea in the United States - producers crush and dry the leaves, which darkens them, oxidizes them and changes their chemistry.

Oolong tea - the kind served in Chinese restaurants - is produced with the same drying process as black tea, but the leaves are dried and darkened for about half as long as leaves that produce black tea.

White tea is harvested in the spring, and its leaves and buds are rapidly steamed and dried after harvest, so it retains many of its catechins and polyphenols, experts say.

Possibly because it is less processed, green tea has higher levels of antioxidants than oolong and black tea, experts say. But there are at least some antioxidants and some theanine in all four types of nonherbal tea.

For the Beltsville study, David Baer, a physiologist with the Diet and Human Performance Lab at ARS, chose oolong tea, in part because it was "kind of halfway" between black and green, meaning it is produced with some oxidation.

The $100,000 study was funded by the U.S. Department of Agriculture, which oversees the lab, and by Suntory, a Japanese beverage distributor that sells tea, whiskey and beer, Baer said.

Previous studies have shown that tea helps the body burn a tiny amount of calories, he said. But scientists have yet to determine if drinking tea burns the kind of fat calories people try to lose when they diet. "There also is a long history of observations that it helps with weight maintenance, but a lot of what we need to know hasn't really been established," Baer said.

As part of the study, Baer also is using blood samples to try to determine if tea consumption affects insulin sensitivity in ways that could benefit diabetics.

Results are expected in about six months, Baer said.

To qualify for the project, volunteers had to be overweight or obese men between 25 and 65. Researchers excluded women because they wanted to measure small changes in fat oxidation levels that can also be affected by menstrual cycles, Baer said.

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