American researchers say drinking tea may help strengthen the body's defense system against infection. Doctors at Brigham and Women's Hospital in Boston, Massachusetts, did the study.

The team studied a chemical found in black, green, oolong and pekoe tea. This chemical is an amino acid called L-theanine. The scientists say it may increase the strength of gamma delta T cells. That's the letter T, not the drink. Gamma delta T cells are part of the body's defenses.

First, the researchers mixed some of these cells with antigens found in the amino acid. Antigens help the body react to infection. Then the scientists added some bacteria. Within twenty-four hours, the cells produced a lot of interferon, a substance that fights infection. Cells not mixed with the antigens did not produce interferon.

In the second part of the study, eleven people drank five to six cups of black tea every day. Ten other people drank the same amount of instant coffee. That is dried coffee mixed with hot water.

Two weeks later, and again two weeks after that, the researchers tested the blood of all twenty-one people. They also looked at what happened when they added bacteria to the blood cells. They found that the tea drinkers produced five times more interferon after they started drinking tea. The coffee drinkers did not produce interferon.

The findings appear in the Proceedings of the National Academy of Sciences. The National Institutes of Health and the Arthritis Foundation provided money for the research.

Doctor Jack Bukowski led the study. He says the antigens added to the gamma delta T cells were responsible for the increased reaction to the bacteria. He says the study also showed that the cells were able to remember the bacteria and fight them again the next time.

Earlier research already has found that tea can help prevent heart disease and cancer. Doctor Bukowski says the new study must be repeated with more people. If the findings are confirmed, he says, then tea drinking might also help protect against bacterial infections. He says the amino acid L-theanine could be removed from tea and used as a drug to strengthen the body's defenses.