Besides being so pleasant to sip and so tasty with cookies, tea has potent antioxidant properties. A recent study reveals yet another way in which tea promotes good health — by boosting the natural ability of the immune system to fend off disease.
This study, published in the Proceedings of the National Academy of Sciences, is the first to offer direct evidence that tea can help the body fight infection caused by pathogens like bacteria and viruses. According to the researchers, this immune-boosting activity also may underlie tea’s protective effects against cancer.
Earlier research has linked tea consumption with protection against heart disease and various types of cancer, an effect attributed to tea’s content of antioxidant polyphenol compounds. The new study showed that drinking five cups of tea a day boosted the activity of the immune system by stimulating the production of important antigens.
The small study compared the immune responses of 21 healthy volunteers who drank either tea or coffee. Analysis of blood samples showed that the 11 tea drinkers, who consumed about 20 ounces of black tea a day for two or four weeks, had significantly stronger immune responses against bacteria than did the 10 coffee drinkers.
According to the researchers, l-theanine, an amino acid in tea, acts as a precursor to an important type of antigen called an alkylamine antigen. Antigens are immune-system components that prompt the body to create antibodies. This interaction between antigens and antibodies is a key aspect of the immune system’s disease-fighting abilities.
Antigens may be formed within the body, or, as is the case with alkylamine antigens, be introduced from outside. Alkylamine antigens are associated with tumor cells, bacteria, parasites and fungi, but also with plant products such as tea, apples, mushrooms and wine. When we drink tea, the liver processes l-theanine into an alkylamine antigen called ethylamine. In turn, ethylamine primes certain immune cells (known as gamma delta T cells) to mount a “memory response” when they encounter the antigen again in the future.
While the study was small, it has important implications for future research on the health benefits of tea. The researchers concluded, “These data provide evidence that dietary intake of tea and perhaps other vegetables and fruits containing alkylamine antigens or their precursors may prime human gamma delta T cells that then can provide natural resistance to microbial infections and perhaps tumors.”
The study used black tea, but green and oolong teas also contain l-theanine. In fact, black, green and oolong teas all come from the same plant, Camellia sinensis. The main difference among these three types of tea lies in the way in which they are processed.
Kamath, A.B., et al. “Antigens in tea-beverage prime human gamma delta T cells in vitro and in vivo for memory and nonmemory antibacterial cytokine responses.” Proceedings of the National Academy of Sciences 2003; 100(10): 6009 – 6014.
Evelyn Leigh is a writer, editor and herbalist who lives to garden in Boulder, Colorado. She is the co-author of the Herb Research Foundation’s science-based book, The Encyclopedia of Popular Herbs (Prima Publishing, 2000).