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.
The 20 volunteers were paid $1,100 each to eat a controlled diet and drink either oolong tea or placebos for five-day stretches.
They went to the Beltsville lab for breakfast and dinner, and were given carryout lunches. Four times a day, they drank 8 ounces of one of five beverages: oolong tea, oolong enriched with green tea compounds, oolong enriched with black tea compounds, water with caffeine and water flavored and colored to look like tea.
The beverages were packaged in cans so volunteers weren't sure which they were drinking.
At the end of each five-day stretch of controlled dieting, each volunteer spent 24 hours confined to the center's "calorimeter," a 9-by-10-foot sealed chamber with at least some of the comforts of home: sink, toilet, flat-screen television, wall phone and laptop computer.
By controlling the air flowing into the chamber, researchers were able to measure the levels of oxygen, carbon dioxide, nitrogen and water vapor coming out.
Using a mass spectrometer, they recorded levels of each gas and classified every single calorie burned as fat, carbohydrate or protein, said William V. Rumpler, the ARS research physiologist who operates the system.
His facility is one of a half-dozen around the country that researchers can use for such detailed studies of human metabolism, Rumpler said.
Between each five-day consumption test, volunteers had two-week intervals without dietary restrictions.
Thomas, an information technology specialist for a Silver Spring firm, volunteered for the study after his wife, an ARS employee, told him about it. It didn't seem like such a bad deal: The food was free and with two kids in college, the cash didn't hurt.
But at times, the experience made him feel a bit like a lab rat. Once inside the calorimeter, his only view of the outside world was through a 3-by-3-foot Plexiglas window that technicians peered through to check his progress.
But since he works as a computer specialist, the Internet allowed him to get work done during his confinement.
"It's really not a whole lot different than just hanging around the house on the weekend," he said. "I get accused of spending too much time on my computer at home anyway."
The food, he added "wasn't bad." The menu varied each day and the quality was generally "kind of comparable to a high-end frozen dinner."
Nor did being confined to a single room for 24 hours bother Thomas much.
There was one drawback. Thomas has never been particularly fond of tea.
"I'm more of a coffee drinker," he said.
dennis.obrien@baltsun.com
Tea facts
Other than water, tea is the most widely consumed beverage in the world. It was reportedly discovered about 5,000 years ago, either in China or India.
Anna, seventh Duchess of Bedford, is credited with establishing the English practice of afternoon tea in 1840, when she began drinking it with a light snack at 4 p.m.
New York merchant John Sullivan gets credit for inventing the tea bag sometime around 1904, when he began shipping tea to customers in silk bags.
"Real" tea comes in black, green, white and oolong varieties, all produced from leaves of Camellia sinensis, a white-flowered evergreen. Herbal teas are made from other plants.
About 75 percent of the tea produced worldwide is black, while 23 percent is green and 2 percent is oolong. Leading tea producers include Argentina, Brazil, China, India, Indonesia and Kenya.
About half of all Americans drink tea, with retail sales reaching about $2 billion last year. About 83 percent of the 2.2 billion gallons consumed in the United States last year was black tea while 16 percent was green tea and the rest was oolong.
About 85 percent of the tea consumed in the U.S. each year is ice tea.
A 6-ounce cup of black tea contains about 40 milligrams of caffeine, less than half the caffeine in a cup of coffee. Green tea contains even less caffeine.
[Source: The Tea Association of the U.S.A. Inc.]