Drinking tea appears to prime the immune system to fight infection and chronic disease, according to US researchers.
There is already a significant body of evidence backing tea's health benefits which focuses mainly on its antioxidant activities. The new research suggests that there may be a further action on health.
In an experiment, people who drank five to six small cups of black tea daily for two weeks were better able to fight off bacterial infections, report the researchers in the early online edition of the Proceedings of the National Academy of Science.
In the study, researchers from Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts measured the activity of gamma delta T cells in people who were not regular tea-drinkers.
Gamma delta T cells act to prevent and reduce the effects of disease. Previous experiments have shown that exposing these cells to ethylamine, produced when the tea ingredient L-theanine is broken down in the liver, boosted the abilities of the cells to fight infections.
Ethylamine is also found in other plant products such as mushrooms, apples, and wine, and has even been shown to attack cancer tumours.
In the lab, the scientists extracted exposed gamma delta T cells from people to ethylamine or to placebo and then mixed both sets with bacteria. Those that had not been exposed to ethylamine showed no signs of fighting the bacteria. However, cells that had been previously exposed to the tea component multiplied ten times, and produced significant disease-fighting chemicals.
The researchers also carried out in vivo studies on people who either drank about 20 ounces of tea a day for two weeks, or consumed coffee instead. The tea drinkers' gamma delta T cells produced a wealth of anti-bacterial chemicals when exposed to bacteria. In contrast, people who drank coffee during the study produced no disease-fighting proteins in response to bacteria.
It is thought that while tea drinkers will still get sick, they may have milder symptoms.