The research, appearing in the April 21-25 issue of the Proceedings of the National Academy of Sciences, adds to the growing list of health benefits researchers have attributed to tea. Previous research has found that the drink can help ward off heart disease and cancer, probably due to its abundance of antioxidants.
The infection-fighting ability of tea, however, is attributed to a substance found in some tea, called L-theanine, which is broken down into a group of chemicals called alkylamine antigens. Antigens are substances that produce antibodies to fight infections.
The new research studied the effects of these antigens on gamma-delta T cells, one of the immune system's infection fighters.
The study was small, cautions the lead author, Dr. Jack Bukowski, an assistant professor of medicine at Harvard Medical School and staff rheumatologist at Brigham and Women's Hospital in Boston. And while his team proved that tea drinkers, compared to coffee drinkers, had more ability to produce disease-fighting chemicals, the researchers did not track whether the tea drinkers actually experienced fewer infections.
Even so, Bukowski says, "there's no downside to drinking tea. I heartily recommend drinking tea."
His team first did work in the laboratory, exposing some cultured human gamma-delta T cells to an alkylamine antigen but not exposing others. Then they exposed the cells to bacteria, simulating an infection. The cells exposed to the antigen produced much interferon, an infection-fighter, in the first 24 hours, Bukowski says, while those not exposed did not produce it.
"The gamma delta T cells were responsible," he says. The study also proved that these cells have a memory, he says, and are able to recognize bacteria the next time and fight them.
Next, Bukowski and his team asked 11 subjects to drink five to six cups of black tea every day, and another 10 people to drink the same quantity of instant coffee. The subjects did this for either two or four weeks.
Then, two weeks into the study, the researchers tested the blood of coffee and tea drinkers by exposing it to bacteria in the lab andcomparing samples taken before the study to those taken two weeks later. "We found they [tea drinkers] made five times more interferon after they started drinking tea compared to before drinking tea," Bukowski says. The coffee drinkers showed no enhanced production ofinterferon.
Not all teas contain L-theanine, Bukowski cautions. Green, black, oolong, or pekoe teas do, he says.
Coffee drinkers might consider cutting down on coffee, he says, and adding tea -- hot or iced -- to their daily intake of beverage.
If the research bears out, tea drinking may prove to offer protection from skin infections caused by bacteria, bacterial pneumonias, and food poisoning, among other ailments, Bukowski says.
Another expert who has researched tea and its antioxidant benefits says the study results make sense.
"These compounds may prime our immune cells so that when they see [bacteria] they are better able to respond," says Jeffrey B. Blumberg. He is a professor and chief of the Antioxidants Research Laboratory and senior scientist at the Jean Mayer USDA Human Nutrition Research Center on Aging in Boston.
"I'm really impressed," Blumberg says of the study's findings. "The responses [in the tea drinkers] were very marked." Blumberg notes, however, that the study was a pilot study, with details such as age of the subjects not available, and that more research is needed.
Still, he adds, "It's a fascinating study."
Besides being present in tea, the alkylamine antigens are found in lower concentrations in apples and mushrooms as well as red and white wine, Bukowski says.
For more information on tea, visit the Tea Association of the United States of America. For details on how the immune system works, check with the National Institute of Allergy and Infectious Diseases.